An authorization by ATC requiring pilots to submit only that information needed for the purpose of ATC. It
includes only a small portion of the usual IFR flight plan information. In certain instances, this may be
only aircraft identification, location, and pilot request. Other information may be requested if needed by
ATC for separation/control purposes. It is frequently used by aircraft which are airborne and desire an
instrument approach or by aircraft which are on the ground and desire a climb to VFR-on-top. (See VFR-ON-TOP.) (Refer to
AIM.)
ABEAM
An aircraft is "abeam" a fix, point, or object when that fix, point, or object is approximately 90 degrees
to the right or left of the aircraft track. Abeam indicates a general position rather than a precise point.
ABORT
To terminate a preplanned aircraft maneuver; e.g., an aborted takeoff.
An intentional maneuver involving an abrupt change in an aircraft's attitude, an abnormal attitude, or
abnormal acceleration not necessary for normal flight. (Refer to
14 CFR Part 91.)
[ICAO] Maneuvers intentionally performed by an aircraft involving an abrupt change in its attitude, an
abnormal attitude, or an abnormal variation in speed.
Departure and/or arrival routes that are adapted in ARTCC ERAM computers to accomplish inter/intrafacility
controller coordination and to ensure that flight data is posted at the proper control positions. Adapted
routes are automatically applied to flight plans where appropriate. When the workload or traffic situation
permits, controllers may provide radar vectors or assign requested routes to minimize circuitous routing.
Adapted routes are usually confined to one ARTCC's area and are referred to by the following names or
abbreviations:
Adapted Arrival Route (AAR). A specific arrival route from an appropriate en route point to an airport
or terminal area. It may be included in a Standard Terminal Arrival (STAR) or a Preferred IFR Route.
Adapted Departure Route (ADR). A specific departure route from an airport or terminal area to an en
route point where there is no further need for flow control. It may be included in an Instrument Departure
Procedure (DP) or a Preferred IFR Route.
Adapted Departure and Arrival Route (ADAR). A route between two terminals which are within or
immediately adjacent to one ARTCC's area. ADARs are similar to Preferred IFR Routes and may share
components, but they are not synonymous.
Advisory information provided by ATC which includes but is not limited to the following:
Traffic advisories.
Vectors, when requested by the pilot, to assist aircraft receiving traffic advisories to avoid observed
traffic.
Altitude deviation information of 300 feet or more from an assigned altitude as observed on a verified
(reading correctly) automatic altitude readout (Mode C).
Advisories that traffic is no longer a factor.
Weather and chaff information.
Weather assistance.
Bird activity information.
Holding pattern surveillance. Additional services are provided to the extent possible contingent only
upon the controller's capability to fit them into the performance of higher priority duties and on the
basis of limitations of the radar, volume of traffic, frequency congestion, and controller workload. The
controller has complete discretion for determining if he/she is able to provide or continue to provide a
service in a particular case. The controller's reason not to provide or continue to provide a service in
a particular case is not subject to question by the pilot and need not be made known to him/her.
A transportation system that transports people and property by air between two points in the NAS using
aircraft with advanced technologies, including electric aircraft or electric vertical takeoff and landing
aircraft, in both controlled and uncontrolled airspace.
ADVISE INTENTIONS
Tell me what you plan to do.
ADVISORY
Advice and information provided to assist pilots in the safe conduct of flight and aircraft movement. (See ADVISORY SERVICE.)
ADVISORY CIRCULAR
An FAA publication, advisory and descriptive in nature, which is not regulatory.
A procedure used by the military to transfer fuel from one aircraft to another during flight. (Refer to
VFR/IFR Wall Planning Charts.)
AERODROME
A defined area on land or water (including any buildings, installations and equipment) intended to be used
either wholly or in part for the arrival, departure, and movement of aircraft.
AERODROME BEACON [ICAO]
Aeronautical beacon used to indicate the location of an aerodrome from the air.
AERODROME CONTROL SERVICE [ICAO]
Air traffic control service for aerodrome traffic.
AERODROME CONTROL TOWER [ICAO]
A unit established to provide air traffic control service to aerodrome traffic.
AERODROME ELEVATION [ICAO]
The elevation of the highest point of the landing area.
AERODROME TRAFFIC CIRCUIT [ICAO]
The specified path to be flown by aircraft operating in the vicinity of an aerodrome.
AERONAUTICAL BEACON
A visual NAVAID displaying flashes of white and/or colored light to indicate the location of an airport, a
heliport, a landmark, a certain point of a Federal airway in mountainous terrain, or an obstruction. (See AIRPORT ROTATING BEACON.) (Refer to
AIM.)
AERONAUTICAL CHART
A map used in air navigation containing all or part of the following: topographic features, hazards and
obstructions, navigation aids, navigation routes, designated airspace, and airports. Commonly used
aeronautical charts are:
Sectional Aeronautical Charts (1:500,000)- Designed for visual navigation of slow or medium speed
aircraft. Topographic information on these charts features the portrayal of relief and a judicious
selection of visual check points for VFR flight. Aeronautical information includes visual and radio aids
to navigation, airports, controlled airspace, permanent special use airspace (SUA), obstructions, and
related data.
VFR Terminal Area Charts (1:250,000)- Depict Class B airspace which provides for the control or
segregation of all the aircraft within Class B airspace. The chart depicts topographic information and
aeronautical information which includes visual and radio aids to navigation, airports, controlled
airspace, permanent SUA, obstructions, and related data.
En Route Low Altitude Charts- Provide aeronautical information for en route instrument navigation (IFR)
in the low altitude stratum. Information includes the portrayal of airways, limits of controlled
airspace, position identification and frequencies of radio aids, selected airports, minimum en route and
minimum obstruction clearance altitudes, airway distances, reporting points, permanent SUA, and related
data. Area charts, which are a part of this series, furnish terminal data at a larger scale in congested
areas.
En Route High Altitude Charts- Provide aeronautical information for en route instrument navigation (IFR)
in the high altitude stratum. Information includes the portrayal of jet routes, identification and
frequencies of radio aids, selected airports, distances, time zones, special use airspace, and related
information.
Instrument Approach Procedures (IAP) Charts- Portray the aeronautical data which is required to execute
an instrument approach to an airport. These charts depict the procedures, including all related data,
and the airport diagram. Each procedure is designated for use with a specific type of electronic
navigation system including NDB, TACAN, VOR, ILS RNAV and GLS. These charts are identified by the type
of navigational aid(s)/equipment required to provide final approach guidance.
Instrument Departure Procedure (DP) Charts- Designed to expedite clearance delivery and to facilitate
transition between takeoff and en route operations. Each DP is presented as a separate chart and may
serve a single airport or more than one airport in a given geographical location.
Standard Terminal Arrival (STAR) Charts Designed to expedite air traffic control arrival procedures and
to facilitate transition between en route and instrument approach operations. Each STAR procedure is
presented as a separate chart and may serve a single airport or more than one airport in a given
geographical location.
Airport Taxi Charts Designed to expedite the efficient and safe flow of ground traffic at an airport.
These charts are identified by the official airport name; e.g., Ronald Reagan Washington National
Airport.
[ICAO] A representation of a portion of the earth, its culture and relief, specifically designated to meet
the requirements of air navigation.
AERONAUTICAL INFORMATION MANUAL (AIM)
A primary FAA publication whose purpose is to instruct airmen about operating in the National Airspace
System of the U.S. It provides basic flight information, ATC Procedures and general instructional
information concerning health, medical facts, factors affecting flight safety, accident and hazard
reporting, and types of aeronautical charts and their use.
AERONAUTICAL INFORMATION PUBLICATION (AIP) [ICAO]
A publication issued by or with the authority of a State and containing aeronautical information of a
lasting character essential to air navigation. (See CHART SUPPLEMENT U.S.)
AERONAUTICAL INFORMATION SERVICES (AIS)
A facility in Silver Spring, MD, established by FAA to operate a central aeronautical information service
for the collection, validation, and dissemination of aeronautical data in support of the activities of
government, industry, and the aviation community. The information is published in the National Flight Data
Digest. see NATIONAL FLIGHT DATA DIGEST.)
An FAA field office serving an assigned geographical area, staffed with Flight Standards personnel serving
the aviation industry and the general public on matters related to the certification and operation of
scheduled air carriers and other large aircraft operations.
AIR DEFENSE EMERGENCY
A military emergency condition declared by a designated authority. This condition exists when an attack upon
the continental U.S., Alaska, Canada, or U.S. installations in Greenland by hostile aircraft or missiles is
considered probable, is imminent, or is taking place. (Refer to
AIM.)
AIR DEFENSE IDENTIFICATION ZONE (ADIZ)
An area of airspace over land or water in which the ready identification, location, and control of all
aircraft (except for Department of Defense and law enforcement aircraft) is required in the interest of
national security.
Note: ADIZ locations and operating and flight plan requirements for civil aircraft operations are
specified in 14 CFR Part 99 (Refer to
AIM.)
AIR NAVIGATION FACILITY
Any facility used in, available for use in, or designed for use in, aid of air navigation, including landing
areas, lights, any apparatus or equipment for disseminating weather information, for signaling, for
radio-directional finding, or for radio or other electrical communication, and any other structure or
mechanism having a similar purpose for guiding or controlling flight in the air or the landing and takeoff
of aircraft. (See NAVIGATIONAL AID.)
AIR ROUTE SURVEILLANCE RADAR
Air route traffic control center (ARTCC) radar used primarily to detect and display an aircraft's position
while en route between terminal areas. The ARSR enables controllers to provide radar air traffic control
service when aircraft are within the ARSR coverage. In some instances, ARSR may enable an ARTCC to provide
terminal radar services similar to but usually more limited than those provided by a radar approach control.
AIR ROUTE TRAFFIC CONTROL CENTER
A facility established to provide air traffic control service to aircraft operating on IFR flight plans
within controlled airspace and principally during the en route phase of flight. When equipment capabilities
and controller workload permit, certain advisory/assistance services may be provided to VFR aircraft. (See EN ROUTE AIR TRAFFIC CONTROL SERVICES.) (Refer to
AIM.)
AIR TAXI
Used to describe a helicopter/VTOL aircraft movement conducted above the surface but normally not above 100
feet AGL. The aircraft may proceed either via hover taxi or flight at speeds more than 20 knots. The pilot
is solely responsible for selecting a safe airspeed/altitude for the operation being conducted. (See HOVER TAXI.) (Refer to
AIM.)
AIR TRAFFIC
Aircraft operating in the air or on an airport surface, exclusive of loading ramps and parking areas.
[ICAO] All aircraft in flight or operating on the maneuvering area of an aerodrome.
AIR TRAFFIC CLEARANCE
An authorization by air traffic control for the purpose of preventing collision between known aircraft, for
an aircraft to proceed under specified traffic conditions within controlled airspace. The pilot-in-command
of an aircraft may not deviate from the provisions of a visual flight rules (VFR) or instrument flight rules
(IFR) air traffic clearance except in an emergency or unless an amended clearance has been obtained.
Additionally, the pilot may request a different clearance from that which has been issued by air traffic
control (ATC) if information available to the pilot makes another course of action more practicable or if
aircraft equipment limitations or company procedures forbid compliance with the clearance issued. Pilots may
also request clarification or amendment, as appropriate, any time a clearance is not fully understood, or
considered unacceptable because of safety of flight. Controllers should, in such instances and to the extent
of operational practicality and safety, honor the pilot's request.
14 CFR Part 91.3(a) states: "The pilot in command
of an aircraft is directly responsible for, and is the final authority as to, the operation of that
aircraft." THE PILOT IS RESPONSIBLE TO REQUEST AN AMENDED CLEARANCE if ATC issues a clearance that would
cause a pilot to deviate from a rule or regulation, or in the pilot's opinion, would place the aircraft in
jeopardy. (See ATC INSTRUCTIONS.) (See ICAO term
AIR TRAFFIC CONTROL CLEARANCE.)
AIR TRAFFIC CONTROL
A service operated by appropriate authority to promote the safe, orderly and expeditious flow of air
traffic. (See ICAO term AIR TRAFFIC CONTROL SERVICE.)
AIR TRAFFIC CONTROL CLEARANCE [ICAO]
Authorization for an aircraft to proceed under conditions specified by an air traffic control unit.
Note 1: For convenience, the term air traffic control clearance is frequently abbreviated to clearance
when used in appropriate contexts.
Note 2: The abbreviated term clearance may be prefixed by the words taxi, takeoff, departure, en route,
approach or landing to indicate the particular portion of flight to which the air traffic control
clearance relates.
AIR TRAFFIC CONTROL SYSTEM COMMAND CENTER (ATCSCC)
An Air Traffic Tactical Operations facility responsible for monitoring and managing the flow of air traffic
throughout the NAS, producing a safe, orderly, and expeditious flow of traffic while minimizing delays. The
following functions are located at the ATCSCC:
Central Altitude Reservation Function (CARF). Responsible for coordinating, planning, and approving
special user requirements under the Altitude Reservation (ALTRV) concept. (See ALTITUDE RESERVATION.)
Airport Reservation Office (ARO). Monitors the operation and allocation of reservations for unscheduled
operations at airports designated by the Administrator as High Density Airports. These airports are
generally known as slot controlled airports. The ARO allocates reservations on a first come, first
served basis determined by the time the request is received at the ARO. (Refer to
14 CFR Part 93.) (See CHART SUPPLEMENT U.S.)
U.S. Notice to Air Missions (NOTAM) Office. Responsible for collecting, maintaining, and distributing
NOTAMs for the U.S. civilian and military, as well as international aviation communities. (See NOTICE TO AIR MISSIONS.)
Weather Unit. Monitor all aspects of weather for the U.S. that might affect aviation including cloud
cover, visibility, winds, precipitation, thunderstorms, icing, turbulence, and more. Provide forecasts
based on observations and on discussions with meteorologists from various National Weather Service
offices, FAA facilities, airlines, and private weather services.
Air Traffic Organization (ATO) Space Operations and Unmanned Aircraft System (UAS); the Office of
Primary Responsibility (OPR) for all space and upper class E tactical operations in the National
Airspace System (NAS).
AIR TRAFFIC SERVICE
A generic term meaning:
Flight Information Service.
Alerting Service.
Air Traffic Advisory Service.
Air Traffic Control Service:
Area Control Service,
Approach Control Service, or
Airport Control Service.
AIR TRAFFIC ORGANIZATION (ATO)
The FAA line of business responsible for providing safe and efficient air navigation services in the national
airspace system.
AIR TRAFFIC SERVICE (ATS) ROUTES
The term "ATS Route" is a generic term that includes "VOR Federal airways," "colored Federal airways," "jet
routes," and "RNAV routes." The term "ATS route" does not replace these more familiar route names, but
serves only as an overall title when listing the types of routes that comprise the United States route
structure.
AIRBORNE
An aircraft is considered airborne when all parts of the aircraft are off the ground.
AIRBORNE DELAY
Amount of delay to be encountered in airborne holding.
AIRBORNE REROUTE (ABRR)
A capability within the Traffic Flow Management System used for the timely development and implementation of
tactical reroutes for airborne aircraft. This capability defines a set of aircraft-specific reroutes that
address a certain traffic flow problem and then electronically transmits them to En Route Automation
Modernization (ERAM) for execution by the appropriate sector controllers.
AIRCRAFT
Device(s) that are used or intended to be used for flight in the air, and when used in air traffic control
terminology, may include the flight crew.
[ICAO] Any machine that can derive support in the atmosphere from the reactions of the air other than the
reactions of the air against the earth's surface.
AIRCRAFT APPROACH CATEGORY
A grouping of aircraft based on a speed of 1.3 times the stall speed in the landing configuration at maximum
gross landing weight. An aircraft must fit in only one category. If it is necessary to maneuver at speeds in
excess of the upper limit of a speed range for a category, the minimums for the category for that speed must
be used. For example, an aircraft which falls in Category A, but is circling to land at a speed in excess of
91 knots, must use the approach Category B minimums when circling to land. The categories are as follows:
Category A Speed less than 91 knots.
Category B Speed 91 knots or more but less than 121 knots.
Category C Speed 121 knots or more but less than 141 knots.
Category D Speed 141 knots or more but less than 166 knots.
For the purposes of Wake Turbulence Separation Minima, ATC classifies aircraft as Super, Heavy, Large, and
Small as follows:
Super. The Airbus A-380-800 (A388) and the Antonov An-225 (A225) are classified as
super.
Heavy. Aircraft capable of takeoff weights of 300,000 pounds or more whether or not
they are operating at this weight during a particular phase of flight.
Large. Aircraft of more than 41,000 pounds, maximum certificated takeoff weight, up to
but not including 300,000 pounds.
Small. Aircraft of 41,000 pounds or less maximum certificated takeoff weight.
Predicted conflict, within EDST of two aircraft, or between aircraft and airspace. A Red alert is used for
conflicts when the predicted minimum separation is 5 nautical miles or less. A Yellow alert is used when the
predicted minimum separation is between 5 and approximately 12 nautical miles. A Blue alert is used for
conflicts between an aircraft and predefined airspace. (See EN ROUTE
DECISION SUPPORT TOOL.)
AIRCRAFT LIST (ACL)
A view available with EDST that lists aircraft currently in or predicted to be in a particular sector's
airspace. The view contains textual flight data information in line format and may be sorted into various
orders based on the specific needs of the sector team. (See EN ROUTE
DECISION SUPPORT TOOL.)
AIRCRAFT SURGE LAUNCH AND RECOVERY
Procedures used at USAF bases to provide increased launch and recovery rates in instrument flight rules
conditions. ASLAR is based on:
Reduced separation between aircraft which is based on time or distance. Standard arrival separation
applies between participants including multiple flights until the DRAG point. The DRAG point is a
published location on an ASLAR approach where aircraft landing second in a formation slows to a
predetermined airspeed. The DRAG point is the reference point at which MARSA applies as expanding
elements effect separation within a flight or between subsequent participating flights.
ASLAR procedures shall be covered in a Letter of Agreement between the responsible USAF military ATC
facility and the concerned Federal Aviation Administration facility. Initial Approach Fix spacing
requirements are normally addressed as a minimum.
AIRCRAFT HAZARD AREA (AHA)
Used by ATC to segregate air traffic from a launch vehicle, reentry vehicle, amateur rocket, jettisoned
stages, hardware, or falling debris generated by failures associated with any of these activities. An AHA is
designated via NOTAM as either a TFR or stationary ALTRV. Unless otherwise specified, the vertical limits of
an AHA are from the surface to unlimited. (See CONTINGENCY HAZARD
AREA.) (See REFINED HAZARD AREA.) (See TRANSITIONAL HAZARD AREA.)
AIRCRAFT WAKE TURBULENCE CATEGORIES
For the purpose of Wake Turbulence Recategorization (RECAT) Separation Minima, ATC groups aircraft into
categories ranging from Category A through Category I, dependent upon the version of RECAT that is applied.
Specific category assignments vary and are listed in the RECAT Orders.
AIRMEN'S METEOROLOGICAL INFORMATION (AIRMET)
A concise description of an occurrence or expected occurrence of specified en route weather phenomena that may
affect the safety of aircraft operations, but at intensities lower than those that require the issuance of a
SIGMET. An AIRMET may be issued when any of the following weather phenomena are occurring or expected to
occur:
An area on land or water that is used or intended to be used for the landing and takeoff of aircraft and
includes its buildings and facilities, if any.
AIRPORT ADVISORY AREA
The area within ten miles of an airport without a control tower or where the tower is not in operation, and
on which a Flight Service Station is located. (See LOCAL AIRPORT
ADVISORY.) (Refer to
AIM.)
AIRPORT ARRIVAL RATE (AAR)
A dynamic input parameter specifying the number of arriving aircraft which an airport or airspace can accept
from the ARTCC per hour. The AAR is used to calculate the desired interval between successive arrival
aircraft.
AIRPORT DEPARTURE RATE (ADR)
A dynamic parameter specifying the number of aircraft which can depart an airport and the airspace can
accept per hour.
Various lighting aids that may be installed on an airport. Types of airport lighting include:
Approach Light System (ALS) An airport lighting facility which provides visual guidance to landing
aircraft by radiating light beams in a directional pattern by which the pilot aligns the aircraft with
the extended centerline of the runway on his/her final approach for landing. Condenser-Discharge
Sequential Flashing Lights/Sequenced Flashing Lights may be installed in conjunction with the ALS at
some airports. Types of Approach Light Systems are:
ALSF-1 Approach Light System with Sequenced Flashing Lights in ILS Cat-I configuration.
ALSF-2 Approach Light System with Sequenced Flashing Lights in ILS Cat-II configuration.
The ALSF-2 may operate as an SSALR when weather conditions permit.
SSALF Simplified Short Approach Light System with Sequenced Flashing Lights.
SSALR Simplified Short Approach Light System with Runway Alignment Indicator Lights.
MALSF Medium Intensity Approach Light System with Sequenced Flashing Lights.
MALSR Medium Intensity Approach Light System with Runway Alignment Indicator Lights.
RLLS Runway Lead-in Light System Consists of one or more series of flashing lights
installed at or near ground level that provides positive visual guidance along an approach path,
either curving or straight, where special problems exist with hazardous terrain, obstructions, or
noise abatement procedures.
RAIL Runway Alignment Indicator Lights Sequenced Flashing Lights which are installed only
in combination with other light systems.
ODALS Omni-directional Approach Lighting System consists of seven omni-directional flashing
lights located in the approach area of a nonprecision runway. Five lights are located on the runway
centerline extended with the first light located 300 feet from the threshold and extending at equal
intervals up to 1,500 feet from the threshold. The other two lights are located, one on each side of
the runway threshold, at a lateral distance of 40 feet from the runway edge, or 75 feet from the
runway edge when installed on a runway equipped with a VASI. (Refer to
FAA
Order JO 6850.2, VISUAL GUIDANCE LIGHTING SYSTEMS.)
Runway Lights/Runway Edge Lights Lights having a prescribed angle of emission used to define
the lateral limits of a runway. Runway lights are uniformly spaced at intervals of approximately 200
feet, and the intensity may be controlled or preset.
Touchdown Zone Lighting Two rows of transverse light bars located symmetrically about the
runway centerline normally at 100 foot intervals. The basic system extends 3,000 feet along the runway.
Runway Centerline Lighting Flush centerline lights spaced at 50-foot intervals beginning 75
feet from the landing threshold and extending to within 75 feet of the opposite end of the runway.
Threshold Lights Fixed green lights arranged symmetrically left and right of the runway
centerline, identifying the runway threshold.
Runway End Identifier Lights (REIL) Two synchronized flashing lights, one on each side of the
runway threshold, which provide rapid and positive identification of the approach end of a particular
runway.
Visual Approach Slope Indicator (VASI) An airport lighting facility providing vertical visual
approach slope guidance to aircraft during approach to landing by radiating a directional pattern of
high intensity red and white focused light beams which indicate to the pilot that he/she is "on path" if
he/she sees red/white, "above path" if white/white, and "below path" if red/red. Some airports serving
large aircraft have three-bar VASIs which provide two visual glide paths to the same runway.
Precision Approach Path Indicator (PAPI) An airport lighting facility, similar to VASI,
providing vertical approach slope guidance to aircraft during approach to landing. PAPIs consist of a
single row of either two or four lights, normally installed on the left side of the runway, and have an
effective visual range of about 5 miles during the day and up to 20 miles at night. PAPIs radiate a
directional pattern of high intensity red and white focused light beams which indicate that the pilot is
"on path" if the pilot sees an equal number of white lights and red lights, with white to the left of
the red; "above path" if the pilot sees more white than red lights; and "below path" if the pilot sees
more red than white lights.
Boundary Lights Lights defining the perimeter of an airport or landing area.
Markings used on runway and taxiway surfaces to identify a specific runway, a runway threshold, a
centerline, a hold line, etc. A runway should be marked in accordance with its present usage such as:
The approximate geometric center of all usable runway surfaces.
AIRPORT RESERVATION OFFICE
Office responsible for monitoring the operation of slot controlled airports. It receives and processes
requests for unscheduled operations at slot controlled airports.
AIRPORT ROTATING BEACON
A visual NAVAID operated at many airports. At civil airports, alternating white and green flashes indicate
the location of the airport. At military airports, the beacons flash alternately white and green, but are
differentiated from civil beacons by dual peaked (two quick) white flashes between the green flashes. (See INSTRUMENT FLIGHT RULES.) (See SPECIAL VFR OPERATIONS.) (See ICAO term
AERODROME BEACON.) (Refer to
AIM.)
AIRPORT SURFACE DETECTION EQUIPMENT (ASDE)
Surveillance equipment specifically designed to detect aircraft, vehicular traffic, and other objects, on
the surface of an airport, and to present the image on a tower display. Used to augment visual observation
by tower personnel of aircraft and/or vehicular movements on runways and taxiways. There are three ASDE
systems deployed in the NAS:
ASDE-3 A Surface Movement Radar.
ASDE-X A system that uses an X-band Surface Movement Radar, multilateration and ADS-B.
Airport Surface Surveillance Capability (ASSC) A system that uses Surface Movement Radar,
multilateration and ADS-B.
AIRPORT SURVEILLANCE RADAR
Approach control radar used to detect and display an aircraft's position in the terminal area. ASR provides
range and azimuth information but does not provide elevation data. Coverage of the ASR can extend up to 60
miles.
A service provided by a control tower for aircraft operating on the movement area and in the vicinity of an
airport. (See MOVEMENT AREA.) (See TOWER.) (See ICAO term
AERODROME CONTROL SERVICE.)
Predicted conflict of an aircraft and active Special Activity Airspace (SAA).
AIRSPACE FLOW PROGRAM (AFP)
AFP is a Traffic Management (TM) process administered by the Air Traffic Control System Command Center
(ATCSCC) where aircraft are assigned an Expect Departure Clearance Time (EDCT) in order to manage capacity
and demand for a specific area of the National Airspace System (NAS). The purpose of the program is to
mitigate the effects of en route constraints. It is a flexible program and may be implemented in various
forms depending upon the needs of the air traffic system.
AIRSPACE HIERARCHY
Within the airspace classes, there is a hierarchy and, in the event of an overlap of airspace: Class A
preempts Class B, Class B preempts Class C, Class C preempts Class D, Class D preempts Class E, and Class E
preempts Class G.
AIRSPEED
The speed of an aircraft relative to its surrounding air mass. The unqualified term "airspeed" means one of
the following:
Indicated Airspeed The speed shown on the aircraft airspeed indicator. This is the speed used
in pilot/controller communications under the general term "airspeed." (Refer to
14 CFR Part 1.)
True Airspeed The airspeed of an aircraft relative to undisturbed air. Used primarily in flight
planning and en route portion of flight. When used in pilot/controller communications, it is referred to
as "true airspeed" and not shortened to "airspeed."
The starting of an aircraft engine while the aircraft is airborne, preceded by engine shutdown during
training flights or by actual engine failure.
AIRWAY
A Class E airspace area established in the form of a corridor, the centerline of which is defined by radio
navigational aids. (See FEDERAL AIRWAYS.) (See ICAO term
AIRWAY.) (Refer to
14 CFR Part 71.) (Refer to
AIM.)
[ICAO] A control area or portion thereof established in the form of corridor equipped with radio
navigational aids.
AIRWAY BEACON
Used to mark airway segments in remote mountain areas. The light flashes Morse Code to identify the beacon
site. (Refer to
AIM.)
A request originated by a flight service station (FSS) or an air route traffic control center (ARTCC) for an
extensive communication search for overdue, unreported, or missing aircraft.
ALERTING SERVICE
A service provided to notify appropriate organizations regarding aircraft in need of search and rescue aid
and assist such organizations as required.
The horizontal distance between the aircraft's current position and a fix measured by an area navigation
system that is not subject to slant range errors.
ALPHANUMERIC DISPLAY
Letters and numerals used to show identification, altitude, beacon code, and other information concerning a
target on a radar display.
ALTERNATE AERODROME [ICAO]
An aerodrome to which an aircraft may proceed when it becomes either impossible or inadvisable to proceed to
or to land at the aerodrome of intended landing.
Note: The aerodrome from which a flight departs may also be an en-route or a destination alternate
aerodrome for the flight.
ALTERNATE AIRPORT
An airport at which an aircraft may land if a landing at the intended airport becomes inadvisable. (See ICAO
term ALTERNATE AERODROME.)
ALTIMETER SETTING
The barometric pressure reading used to adjust a pressure altimeter for variations in existing atmospheric
pressure or to the standard altimeter setting (29.92). (Refer to
14 CFR Part 91.) (Refer to
AIM.)
ALTITUDE
The height of a level, point, or object measured in feet Above Ground Level (AGL) or from Mean Sea Level
(MSL). (See FLIGHT LEVEL.)
MSL Altitude Altitude expressed in feet measured from mean sea level.
AGL Altitude Altitude expressed in feet measured above ground level.
Indicated Altitude The altitude as shown by an altimeter. On a pressure or barometric altimeter
it is altitude as shown uncorrected for instrument error and uncompensated for variation from standard
atmospheric conditions.
[ICAO] The vertical distance of a level, a point or an object considered as a point, measured from mean sea
level (MSL).
ALTITUDE READOUT
An aircraft's altitude, transmitted via the Mode C transponder feature, that is visually displayed in
100-foot increments on a radar scope having readout capability. (See
ALPHANUMERIC DISPLAY.) (Refer to
AIM.)
An altitude or altitudes, stated in the order flown, which are to be maintained until reaching a specific
point or time. Altitude restrictions may be issued by ATC due to traffic, terrain, or other airspace
considerations.
ALTITUDE RESTRICTIONS ARE CANCELED
Adherence to previously imposed altitude restrictions is no longer required during a climb or descent.
Authorization by ATC for a pilot to conduct an instrument approach. The type of instrument approach for
which a clearance and other pertinent information is provided in the approach clearance when required. (See CLEARED APPROACH.) (See INSTRUMENT
APPROACH PROCEDURE.) (Refer to
AIM.)
(Refer to 14 CFR Part 91.)
Air traffic control service provided by an approach control facility for arriving and departing VFR/IFR
aircraft and, on occasion, en route aircraft. At some airports not served by an approach control facility,
the ARTCC provides limited approach control service. (See ICAO term
APPROACH CONTROL SERVICE.) (Refer to
AIM.)
[ICAO] Air traffic control service for arriving or departing controlled flights.
APPROACH GATE
An imaginary point used within ATC as a basis for vectoring aircraft to the final approach course. The gate
will be established along the final approach course 1 mile from the final approach fix on the side away from
the airport and will be no closer than 5 miles from the landing threshold.
APPROACH/DEPARTURE HOLD AREA
The locations on taxiways in the approach or departure areas of a runway designated to protect landing or
departing aircraft. These locations are identified by signs and markings.
The order in which aircraft are positioned while on approach or awaiting approach clearance. (See LANDING SEQUENCE.)
[ICAO] The order in which two or more aircraft are cleared to approach to land at the aerodrome.
APPROACH SPEED
The recommended speed contained in aircraft manuals used by pilots when making an approach to landing. This
speed will vary for different segments of an approach as well as for aircraft weight and configuration.
APPROACH WITH VERTICAL GUIDANCE (APV)
A term used to describe RNAV approach procedures that provide lateral and vertical guidance but do not meet
the requirements to be considered a precision approach.
APPROPRIATE ATS AUTHORITY [ICAO]
The relevant authority designated by the State responsible for providing air traffic services in the
airspace concerned. In the United States, the "appropriate ATS authority" is the Program Director for Air
Traffic Planning and Procedures, ATP-1.
APPROPRIATE AUTHORITY
Regarding flight over the high seas: the relevant authority is the State of Registry.
Regarding flight over other than the high seas: the relevant authority is the State having sovereignty
over the territory being overflown.
A defined area on an airport or heliport intended to accommodate aircraft for purposes of loading or
unloading passengers or cargo, refueling, parking, or maintenance. With regard to seaplanes, a ramp is used
for access to the apron from the water.
[ICAO] A defined area, on a land aerodrome, intended to accommodate aircraft for purposes of loading or
unloading passengers, mail or cargo, refueling, parking or maintenance.
ARC
The track over the ground of an aircraft flying at a constant distance from a navigational aid by reference
to distance measuring equipment (DME).
AREA CONTROL CENTER [ICAO]
An air traffic control facility primarily responsible for ATC services being provided IFR aircraft during
the en route phase of flight. The U.S. equivalent facility is an air route traffic control center (ARTCC).
AREA NAVIGATION (RNAV)
A method of navigation which permits aircraft operation on any desired flight path within the coverage of
ground or space based navigation aids or within the limits of the capability of self-contained aids, or a
combination of these.
Note: Area navigation includes performance based navigation as well as other operations that do not meet
the definition of performance based navigation.
AREA NAVIGATION (RNAV) APPROACH CONFIGURATION
STANDARD T An RNAV approach whose design allows direct flight to any one of three initial
approach fixes (IAF) and eliminates the need for procedure turns. The standard design is to align the
procedure on the extended centerline with the missed approach point (MAP) at the runway threshold, the
final approach fix (FAF), and the initial approach/intermediate fix (IAF/IF). The other two IAFs will be
established perpendicular to the IF.
MODIFIED T An RNAV approach design for single or multiple runways where terrain or operational
constraints do not allow for the standard T. The "T" may be modified by increasing or decreasing the
angle from the corner IAF(s) to the IF or by eliminating one or both corner IAFs.
STANDARD I An RNAV approach design for a single runway with both corner IAFs eliminated. Course
reversal or radar vectoring may be required at busy terminals with multiple runways.
TERMINAL ARRIVAL AREA (TAA) The TAA is controlled airspace established in conjunction with the
Standard or Modified T and I RNAV approach configurations. In the standard TAA, there are three areas:
straight-in, left base, and right base. The arc boundaries of the three areas of the TAA are published
portions of the approach and allow aircraft to transition from the en route structure direct to the
nearest IAF. TAAs will also eliminate or reduce feeder routes, departure extensions, and procedure turns
or course reversal.
STRAIGHT-IN AREA A 30NM arc centered on the IF bounded by a straight line extending through
the IF perpendicular to the intermediate course.
LEFT BASE AREA A 30NM arc centered on the right corner IAF. The area shares a boundary with
the straight-in area except that it extends out for 30NM from the IAF and is bounded on the other
side by a line extending from the IF through the FAF to the arc.
RIGHT BASE AREA A 30NM arc centered on the left corner IAF. The area shares a boundary with
the straight-in area except that it extends out for 30NM from the IAF and is bounded on the other
side by a line extending from the IF through the FAF to the arc.
AREA NAVIGATION (RNAV) GLOBAL POSITIONING SYSTEM (GPS) PRECISION RUNWAY MONITORING (PRM) APPROACH
A GPS approach, which requires vertical guidance, used in lieu of an PRM approach to conduct approaches to
parallel runways whose extended centerlines are separated by less than 4,300 feet and at least 3,000 feet,
where simultaneous close parallel approaches are permitted. Also used in lieu of an ILS PRM and/or LDA PRM
approach to conduct Simultaneous Offset Instrument Approach (SOIA) operations.
ARMY AVIATION FLIGHT INFORMATION BULLETIN
A bulletin that provides air operation data covering Army, National Guard, and Army Reserve aviation
activities.
A safety device consisting of two major components, namely, engaging or catching devices and energy
absorption devices for the purpose of arresting both tailhook and/or non-tailhook equipped aircraft. It is
used to prevent aircraft from overrunning runways when the aircraft cannot be stopped after landing or
during aborted takeoff. Arresting systems have various names; e.g., arresting gear, hook device, wire
barrier cable. (See ABORT.) (Refer to
AIM.)
ARRIVAL CENTER
The ARTCC having jurisdiction for the impacted airport.
ARRIVAL DELAY
A parameter which specifies a period of time in which no aircraft will be metered for arrival at the
specified airport.
ARRIVAL/DEPARTURE WINDOW (ADW)
A depiction presented on an air traffic control display, used by the controller to prevent possible
conflicts between arrivals to, and departures from, a runway. The ADW identifies that point on the final
approach course by which a departing aircraft must have begun takeoff.
ARRIVAL SECTOR (En Route)
An operational control sector containing one or more meter fixes on or near the TRACON boundary.
Used to prefix a message of noncontrol information when it is relayed to an aircraft by other than an air
traffic controller. (See ADVISORY.)
ATC ASSIGNED AIRSPACE
Airspace of defined vertical/lateral limits, assigned by ATC, for the purpose of providing air traffic
segregation between the specified activities being conducted within the assigned airspace and other IFR air
traffic. (See SPECIAL USE AIRSPACE.)
Used to prefix an ATC clearance when it is relayed to an aircraft by other than an air traffic controller.
ATC INSTRUCTIONS
Directives issued by air traffic control for the purpose of requiring a pilot to take specific actions;
e.g., "Turn left heading two five zero," "Go around," "Clear the runway." (Refer to
14 CFR Part 91.)
Preferred routes that are not automatically applied by Host.
ATC REQUESTS
Used to prefix an ATC request when it is relayed to an aircraft by other than an air traffic controller.
ATC SECURITY SERVICES
Communications and security tracking provided by an ATC facility in support of the DHS, the DOD, or other
Federal security elements in the interest of national security. Such security services are only applicable
within designated areas. ATC security services do not include ATC basic radar services or flight following.
ATC SECURITY SERVICES POSITION
The position responsible for providing ATC security services as defined. This position does not provide ATC,
IFR separation, or VFR flight following services, but is responsible for providing security services in an
area comprising airspace assigned to one or more ATC operating sectors. This position may be combined with
control positions.
ATC SECURITY TRACKING
The continuous tracking of aircraft movement by an ATC facility in support of the DHS, the DOD, or other
security elements for national security using radar (i.e., radar tracking) or other means (e.g., manual
tracking) without providing basic radar services (including traffic advisories) or other ATC services not
defined in this section.
ATS SURVEILLANCE SERVICE [ICAO]
A term used to indicate a service provided directly by means of an ATS surveillance system.
ATC SURVEILLANCE SOURCE
Used by ATC for establishing identification, control and separation using a target depicted on an air
traffic control facility's video display that has met the relevant safety standards for operational use and
received from one, or a combination, of the following surveillance sources:
A generic term meaning variously, ADS-B, PSR, SSR or any comparable ground-based system that enables the
identification of aircraft.
Note: A comparable ground-based system is one that has been demonstrated, by comparative assessment or
other methodology, to have a level of safety and performance equal to or better than monopulse SSR.
A specified route designed for channeling the flow of traffic as necessary for the provision of air traffic
services.
Note: The term "ATS Route" is used to mean variously, airway, advisory route, controlled or uncontrolled
route, arrival or departure, etc.
ATTENTION ALL USERS PAGE (AAUP)
The AAUP provides the pilot with additional information relative to conducting a specific operation, for
example, PRM approaches and RNAV departures.
AUTOLAND APPROACH
An autoland system aids by providing control of aircraft systems during a precision instrument approach to
at least decision altitude and possibly all the way to touchdown, as well as in some cases, through the
landing rollout. The autoland system is a sub-system of the autopilot system from which control surface
management occurs. The aircraft autopilot sends instructions to the autoland system and monitors the
autoland system performance and integrity during its execution.
A precoordinated process, specifically defined in facility directives, during which a transfer of altitude
control and/or radar identification is accomplished without verbal coordination between controllers using
information communicated in a full data block.
AUTOMATED MUTUAL-ASSISTANCE VESSEL RESCUE SYSTEM
A facility which can deliver, in a matter of minutes, a surface picture (SURPIC) of vessels in the area of a
potential or actual search and rescue incident, including their predicted positions and their
characteristics. (See FAA Order JO 7110.65, Para 10-6-4, INFLIGHT
CONTINGENCIES.)
AUTOMATED PROBLEM DETECTION (APD)
An Automation Processing capability that compares trajectories in order to predict conflicts.
AUTOMATED PROBLEM DETECTION BOUNDARY (APB)
The adapted distance beyond a facilities boundary defining the airspace within which EDST performs conflict
detection. (See EN ROUTE DECISION SUPPORT TOOL.)
AUTOMATED PROBLEM DETECTION INHIBITED AREA (APDIA)
Airspace surrounding a terminal area within which APD is inhibited for all flights within that airspace.
AUTOMATED TERMINAL PROXIMITY ALERT (ATPA)
Monitors the separation of aircraft on the Final Approach Course (FAC), displaying a graphical notification
(cone and/or mileage) when a potential loss of separation is detected. The warning cone (Yellow) will
display at 45 seconds and the alert cone (Red) will display at 24 seconds prior to predicted loss of
separation. Current distance between two aircraft on final will be displayed in line 3 of the full data
block of the trailing aircraft in corresponding colors.
AUTOMATED WEATHER SYSTEM
Any of the automated weather sensor platforms that collect weather data at airports and disseminate the
weather information via radio and/or landline. The systems currently consist of the Automated Surface
Observing System (ASOS), Automated Weather Sensor System (AWSS) and Automated Weather Observation System
(AWOS).
AUTOMATED UNICOM
Provides completely automated weather, radio check capability and airport advisory information on an
Automated UNICOM system. These systems offer a variety of features, typically selectable by microphone
clicks, on the UNICOM frequency. Availability will be published in the Chart Supplement U.S. and approach
charts.
That function of a transponder which responds to Mode C interrogations by transmitting the aircraft's
altitude in 100-foot increments.
AUTOMATIC CARRIER LANDING SYSTEM
U.S. Navy final approach equipment consisting of precision tracking radar coupled to a computer data link to
provide continuous information to the aircraft, monitoring capability to the pilot, and a backup approach
system.
AUTOMATIC DEPENDENT SURVEILLANCE (ADS) [ICAO]
A surveillance technique in which aircraft automatically provide, via a data link, data derived from onboard
navigation and position fixing systems, including aircraft identification, four dimensional position and
additional data as appropriate.
A data link position reporting system, controlled by a ground station, that establishes contracts with an
aircraft's avionics that occur automatically whenever specific events occur, or specific time intervals are
reached.
AUTOMATIC DEPENDENT SURVEILLANCE-BROADCAST IN (ADS-B In)
A datalink translation function of the ADSB ground system required to accommodate the two separate operating
frequencies (978 MHz and 1090 ES). The ADSB system receives the ADSB messages transmitted on one frequency
and ADSR translates and reformats the information for rebroadcast and use on the other frequency. This
allows ADSB In equipped aircraft to see nearby ADSB Out traffic regardless of the operating link of the
other aircraft. Aircraft operating on the same ADSB frequency exchange information directly and do not
require the ADSR translation function.
AUTOMATIC DIRECTION FINDER
An aircraft radio navigation system which senses and indicates the direction to a L/MF nondirectional radio
beacon (NDB) ground transmitter. Direction is indicated to the pilot as a magnetic bearing or as a relative
bearing to the longitudinal axis of the aircraft depending on the type of indicator installed in the
aircraft. In certain applications, such as military, ADF operations may be based on airborne and ground
transmitters in the VHF/UHF frequency spectrum. (See BEARING.) (See NONDIRECTIONAL BEACON.)
AUTOMATIC FLIGHT INFORMATION SERVICE (AFIS) ALASKA FSSs ONLY
The continuous broadcast of recorded noncontrol information at airports in Alaska where a FSS provides local
airport advisory service. The AFIS broadcast automates the repetitive transmission of essential but routine
information such as weather, wind, altimeter, favored runway, breaking action, airport NOTAMs, and other
applicable information. The information is continuously broadcast over a discrete VHF radio frequency
(usually the ASOS/ AWSS/AWOS frequency.)
AUTOMATIC TERMINAL INFORMATION SERVICE
The continuous broadcast of recorded noncontrol information in selected terminal areas. Its purpose is to
improve controller effectiveness and to relieve frequency congestion by automating the repetitive
transmission of essential but routine information; e.g., "Los Angeles information Alfa. One three zero zero
Coordinated Universal Time. Weather, measured ceiling two thousand overcast, visibility three, haze, smoke,
temperature seven one, dew point five seven, wind two five zero at five, altimeter two niner niner six.
I-L-S Runway Two Five Left approach in use, Runway Two Five Right closed, advise you have Alfa." (Refer to
AIM.)
[ICAO] The provision of current, routine information to arriving and departing aircraft by means of
continuous and repetitive broadcasts throughout the day or a specified portion of the day.
AUTOROTATION
A rotorcraft flight condition in which the lifting rotor is driven entirely by action of the air when the
rotorcraft is in motion.
Autorotative Landing/Touchdown Autorotation. Used by a pilot to indicate that the landing will
be made without applying power to the rotor.
Low Level Autorotation. Commences at an altitude well below the traffic pattern, usually below
100 feet AGL and is used primarily for tactical military training.
180 degrees Autorotation. Initiated from a downwind heading and is commenced well inside the
normal traffic pattern. "Go around" may not be possible during the latter part of this maneuver.
AVAILABLE LANDING DISTANCE (ALD)
The portion of a runway available for landing and roll-out for aircraft cleared for LAHSO. This distance is
measured from the landing threshold to the hold-short point.
AVIATION WATCH NOTIFICATION MESSAGE
The Storm Prediction Center (SPC) issues Aviation Watch Notification Messages (SAW) to provide an area
threat alert for the aviation meteorology community to forecast organized severe thunderstorms that may
produce tornadoes, large hail, and/or convective damaging winds as indicated in Public Watch Notification
Messages within the Continental U.S. A SAW message provides a description of the type of watch issued by
SPC, a valid time, an approximation of the area in a watch, and primary hazard(s).
AVIATION WEATHER SERVICE
A service provided by the National Weather Service (NWS) and FAA which collects and disseminates pertinent
weather information for pilots, aircraft operators, and ATC. Available aviation weather reports and
forecasts are displayed at each NWS office and FAA FSS. (See
TRANSCRIBED WEATHER BROADCAST.) (See WEATHER ADVISORY.) (Refer to
AIM.)
B
B4UFLY
A free downloadable application, which allows operators to check airspace and local advisories before
flying.
BACK-TAXI
A term used by air traffic controllers to taxi an aircraft on the runway opposite to the traffic flow. The
aircraft may be instructed to back-taxi to the beginning of the runway or at some point before reaching the
runway end for the purpose of departure or to exit the runway.
The horizontal direction to or from any point, usually measured clockwise from true north, magnetic north,
or some other reference point through 360 degrees. (See NONDIRECTIONAL
BEACON.)
BELOW MINIMUMS
Weather conditions below the minimums prescribed by regulation for the particular action involved; e.g.,
landing minimums, takeoff minimums.
BEYOND VISUAL LINE OF SIGHT (BVLOS)
The operation of a UAS beyond the visual capability of the flight crew members (i.e., remote pilot in
command [RPIC], the person manipulating the controls, and visual observer [VO]), if used to see the aircraft
with vision unaided by any device other than corrective lenses, spectacles, and contact lenses.
BLAST FENCE
A barrier that is used to divert or dissipate jet or propeller blast.
BLAST PAD
A surface adjacent to the ends of a runway provided to reduce the erosive effect of jet blast and propeller
wash.
BLIND SPEED
The rate of departure or closing of a target relative to the radar antenna at which cancellation of the
primary radar target by moving target indicator (MTI) circuits in the radar equipment causes a reduction or
complete loss of signal. (See ICAO term BLIND VELOCITY.)
BLIND SPOT
An area from which radio transmissions and/or radar echoes cannot be received. The term is also used to
describe portions of the airport not visible from the control tower.
BRAKING ACTION (GOOD, GOOD TO MEDIUM, MEDIUM, MEDIUM TO POOR, POOR, OR NIL)
A report of conditions on the airport movement area providing a pilot with a degree/quality of braking to
expect. Braking action is reported in terms of good, good to medium, medium, medium to poor, poor, or
nil.(See RUNWAY CONDITION READING.) (See RUNWAY CONDITION REPORT.) (See RUNWAY CONDITION CODES.)
BRAKING ACTION ADVISORIES
When tower controllers receive runway braking action reports which include the terms "medium," "poor," or
"nil," or whenever weather conditions are conducive to deteriorating or rapidly changing runway braking
conditions, the tower will include on the ATIS broadcast the statement, "Braking Action Advisories are in
Effect." During the time braking action advisories are in effect, ATC will issue the most current braking
action report for the runway in use to each arriving and departing aircraft. Pilots should be prepared for
deteriorating braking conditions and should request current runway condition information if not issued by
controllers. Pilots should also be prepared to provide a descriptive runway condition report to controllers
after landing.
BREAKOUT
A technique to direct aircraft out of the approach stream. In the context of simultaneous (independent)
parallel operations, a breakout is used to direct threatened aircraft away from a deviating aircraft.
BROADCAST
Transmission of information for which an acknowledgment is not expected.
[ICAO] A transmission of information relating to air navigation that is not addressed to a specific station
or stations.
BUFFER AREA
As applied to an MVA or MIA chart, a depicted 3 NM or 5 NM radius MVA/MIA sector isolating a displayed
obstacle for which the sector is established. A portion of a buffer area can also be inclusive of a MVA/MIA
sector polygon boundary.
A term that may be used in place of tentative or actual calculated landing time, whichever applies.
CALIBRATED AIRSPEED (CAS)
The indicated airspeed of an aircraft, corrected for position and instrument error. Calibrated airspeed is
equal to true airspeed in standard atmosphere at sea level.
CALL FOR RELEASE
Wherein the overlying ARTCC requires a terminal facility to initiate verbal coordination to secure ARTCC
approval for release of a departure into the en route environment.
CALL UP
Initial voice contact between a facility and an aircraft, using the identification of the unit being called
and the unit initiating the call. (Refer to
AIM.)
CANADIAN MINIMUM NAVIGATION PERFORMANCE SPECIFICATION AIRSPACE
That portion of Canadian domestic airspace within which MNPS separation may be applied.
CARDINAL ALTITUDES
"Odd" or "Even" thousand-foot altitudes or flight levels; e.g., 5,000, 6,000, 7,000, FL 250, FL 260, FL 270.
(See ALTITUDE.) (See FLIGHT LEVEL.)
A fix/waypoint that serves as a transition point from the high altitude waypoint navigation structure to an
arrival procedure (STAR) or the low altitude groundbased navigation structure.
The heights above the earth's surface of the lowest layer of clouds or obscuring phenomena that is reported
as "broken," "overcast," or "obscuration," and not classified as "thin" or "partial."
[ICAO] The height above the ground or water of the base of the lowest layer of cloud below 6,000 meters
(20,000 feet) covering more than half the sky.
The specified airspace within which an air route traffic control center (ARTCC) provides air traffic control
and advisory service. (See AIR ROUTE TRAFFIC CONTROL CENTER.)
(Refer to
AIM.)
CENTER WEATHER ADVISORY
An unscheduled weather advisory issued by Center Weather Service Unit meteorologists for ATC use to alert
pilots of existing or anticipated adverse weather conditions within the next 2 hours. A CWA may modify or
redefine a SIGMET. (See AWW.) (See
AIRMET.) (See CONVECTIVE SIGMET.) (See GRAPHICAL AIRMEN'S METEOROLOGICAL INFORMATION.)
(See SAW.) (See SIGMET.) (Refer to
AIM.)
CENTRAL EAST PACIFIC
An organized route system between the U.S. West Coast and Hawaii.
Thin, narrow metallic reflectors of various lengths and frequency responses, used to reflect radar energy.
These reflectors when dropped from aircraft and allowed to drift downward result in large targets on the
radar display.
CHART SUPPLEMENT U.S.
A publication designed primarily as a pilot's operational manual containing all airports, seaplane bases,
and heliports open to the public including communications data, navigational facilities, and certain special
notices and procedures. This publication is issued in seven volumes according to geographical area.
CHARTED VFR FLYWAYS
Charted VFR Flyways are flight paths recommended for use to bypass areas heavily traversed by large
turbine-powered aircraft. Pilot compliance with recommended flyways and associated altitudes is strictly
voluntary. VFR Flyway Planning charts are published on the back of existing VFR Terminal Area charts.
CHARTED VISUAL FLIGHT PROCEDURE APPROACH
An approach conducted while operating on an instrument flight rules (IFR) flight plan which authorizes the
pilot of an aircraft to proceed visually and clear of clouds to the airport via visual landmarks and other
information depicted on a charted visual flight procedure. This approach must be authorized and under the
control of the appropriate air traffic control facility. Weather minimums required are depicted on the
chart.
CHASE
An aircraft flown in proximity to another aircraft normally to observe its performance during training or
testing.
Light Chop- Turbulence that causes slight, rapid and somewhat rhythmic bumpiness without appreciable
changes in altitude or attitude.
Moderate Chop- Turbulence similar to Light Chop but of greater intensity. It causes rapid bumps or jolts
without appreciable changes in aircraft altitude or attitude.
A maneuver initiated by the pilot to align the aircraft with a runway for landing when a straight-in landing
from an instrument approach is not possible or is not desirable. At tower controlled airports, this maneuver
is made only after ATC authorization has been obtained and the pilot has established required visual
reference to the airport. (See CIRCLE TO RUNWAY.)(See LANDING MINIMUMS.) (Refer to
AIM.)
CIRCLE TO RUNWAY (RUNWAY NUMBER)
Used by ATC to inform the pilot that he/she must circle to land because the runway in use is other than the
runway aligned with the instrument approach procedure. When the direction of the circling maneuver in
relation to the airport/runway is required, the controller will state the direction (eight cardinal compass
points) and specify a left or right downwind or base leg as appropriate; e.g., "Cleared VOR Runway Three Six
Approach circle to Runway Two Two," or "Circle northwest of the airport for a right downwind to Runway Two
Two." (See CIRCLE-TO-LAND MANEUVER.) (See
LANDING MINIMUMS.) (Refer to
AIM.)
Airspace that is not designated in
14 CFR Part 71 as Class A,
Class B, Class C, Class D, or Class E controlled airspace is Class G (uncontrolled) airspace.
CLEAR AIR TURBULENCE (CAT)
Turbulence encountered in air where no clouds are present. This term is commonly applied to high-level
turbulence associated with wind shear. CAT is often encountered in the vicinity of the jet stream. (See WIND SHEAR.) (See JET STREAM.)
CLEAR OF THE RUNWAY
Taxiing aircraft, which is approaching a runway, is clear of the runway when all parts of the aircraft
are held short of the applicable runway holding position marking.
A pilot or controller may consider an aircraft, which is exiting or crossing a runway, to be clear of
the runway when all parts of the aircraft are beyond the runway edge and there are no restrictions to
its continued movement beyond the applicable runway holding position marking.
Pilots and controllers shall exercise good judgment to ensure that adequate separation exists between
all aircraft on runways and taxiways at airports with inadequate runway edge lines or holding position
markings.
The fix, point, or location to which an aircraft is cleared when issued an air traffic clearance.
[ICAO] The point to which an aircraft is granted an air traffic control clearance.
CLEARANCE VOID IF NOT OFF BY (TIME)
Used by ATC to advise an aircraft that the departure release is automatically canceled if takeoff is not made
prior to a specified time. The expiration of a clearance void time does not cancel the departure clearance or
IFR flight plan. It withdraws the pilot's authority to depart IFR until a new departure release/release time
has been issued by ATC. Pilots who choose to depart VFR after their clearance void time has expired should not
depart using the previously assigned IFR transponder code. (See ICAO term CLEARANCE VOID TIME.)
CLEARANCE VOID TIME [ICAO]
A time specified by an air traffic control unit at which a clearance ceases to be valid unless the aircraft
concerned has already taken action to comply therewith.
CLEARED APPROACH
ATC authorization for an aircraft to execute any standard or special instrument approach procedure for that
airport. Normally, an aircraft will be cleared for a specific instrument approach procedure. (See CLEARED (Type of) APPROACH.) (See INSTRUMENT APPROACH PROCEDURE.) (Refer to
14 CFR Part 91.) (Refer to
AIM.)
Means the aircraft is cleared to proceed in accordance with the route of flight filed in the flight plan.
This clearance does not include the altitude, DP, or DP Transition. (See REQUEST FULL ROUTE CLEARANCE.) (Refer to
AIM.)
CLEARED FOR TAKEOFF
ATC authorization for an aircraft to depart. It is predicated on known traffic and known physical airport
conditions.
CLEARED FOR THE OPTION
ATC authorization for an aircraft to make a touch-and-go, low approach, missed approach, stop and go, or
full stop landing at the discretion of the pilot. It is normally used in training so that an instructor can
evaluate a student's performance under changing situations. Pilots should advise ATC if they decide to
remain on the runway, of any delay in their stop and go, delay clearing the runway, or are unable to comply
with the instruction(s). (See OPTION APPROACH.) (Refer to
AIM.)
CLEARED THROUGH
ATC authorization for an aircraft to make intermediate stops at specified airports without refiling a flight
plan while en route to the clearance limit.
CLEARED TO LAND
ATC authorization for an aircraft to land. It is predicated on known traffic and known physical airport
conditions.
CLEARWAY
An area beyond the takeoff runway under the control of airport authorities within which terrain or fixed
obstacles may not extend above specified limits. These areas may be required for certain turbine-powered
operations and the size and upward slope of the clearway will differ depending on when the aircraft was
certificated. (Refer to 14 CFR Part 1.)
CLIMB TO VFR
ATC authorization for an aircraft to climb to VFR conditions within Class B, C, D, and E surface areas when
the only weather limitation is restricted visibility. The aircraft must remain clear of clouds while
climbing to VFR. (See SPECIAL VFR CONDITIONS.) (Refer to
AIM.)
CLIMBOUT
That portion of flight operation between takeoff and the initial cruising altitude.
CLIMB VIA
An abbreviated ATC clearance that requires compliance with the procedure lateral path, associated speed
restrictions, and altitude restrictions along the cleared route or procedure.
CLOSE PARALLEL RUNWAYS
Two parallel runways whose extended centerlines are separated by less than 4,300 feet and at least 3000 feet
(750 feet for SOIA operations) that are authorized to conduct simultaneous independent approach operations.
PRM and simultaneous close parallel appear in approach title. Dual communications, special pilot training,
an Attention All Users Page (AAUP), NTZ monitoring by displays that have aural and visual alerting
algorithms are required. A high update rate surveillance sensor is required for certain runway or approach
course spacing.
CLOSED LOOP CLEARANCE
A vector or reroute clearance that includes a return to route point and updates ERAM to accurately reflect
the anticipated route (e.g., a QU route pick that anticipates length of vector and includes the next fix
that ties into the route of flight.)
CLOSED RUNWAY
A runway that is unusable for aircraft operations. Only the airport management/military operations office
can close a runway.
CLOSED TRAFFIC
Successive operations involving takeoffs and landings or low approaches where the aircraft does not exit the
traffic pattern.
CLOUD
A cloud is a visible accumulation of minute water droplets and/or ice particles in the atmosphere above the
Earth's surface. Cloud differs from ground fog, fog, or ice fog only in that the latter are, by definition,
in contact with the Earth's surface.
In radar operations, clutter refers to the reception and visual display of radar returns caused by
precipitation, chaff, terrain, numerous aircraft targets, or other phenomena. Such returns may limit or
preclude ATC from providing services based on radar. (See CHAFF.) (See GROUND CLUTTER.) (See PRECIPITATION.) (See TARGET.) (See ICAO term
RADAR CLUTTER.)
A navigation aid or intersection where an aircraft transitions between the domestic route structure and the
oceanic route structure.
CODES
The number assigned to a particular multiple pulse reply signal transmitted by a transponder. (See DISCRETE CODE.)
COLD TEMPERATURE CORRECTION
A correction in feet, based on height above airport and temperature, that is added to the aircraft's
indicated altitude to offset the effect of cold temperature on true altitude.
COLLABORATIVE TRAJECTORY OPTIONS PROGRAM (CTOP)
A traffic management program administered by the Air Traffic Control System Command Center (ATCSCC) that
manages demand through constrained airspace, while considering operator preference with regard to both route
and delay as defined in a Trajectory Options Set (TOS).
A significant point over which two or more aircraft will report passing or have reported passing before
proceeding on the same or diverging tracks. To establish/maintain longitudinal separation, a controller may
determine a common point not originally in the aircraft's flight plan and then clear the aircraft to fly
over the point. (See SIGNIFICANT POINT.)
A membership-based entity, described under Section 501(a,c), whose mission is the furtherance of model
aviation. (see also, 49 United States Code (USC) §44809 (h) and Advisory Circular (AC) 91-57).
COMPASS LOCATOR
A low power, low or medium frequency (L/MF) radio beacon installed at the site of the outer or middle marker
of an instrument landing system (ILS). It can be used for navigation at distances of approximately 15 miles
or as authorized in the approach procedure.
Outer Compass Locator (LOM) A compass locator installed at the site of the outer marker of an instrument
landing system. (See OUTER MARKER.)
Middle Compass Locator (LMM) A compass locator installed at the site of the middle marker of an
instrument landing system.
A circle, graduated in degrees, printed on some charts or marked on the ground at an airport. It is used as
a reference to either true or magnetic direction.
COMPLY WITH RESTRICTIONS
An ATC instruction that requires an aircraft being vectored back onto an arrival or departure procedure to
comply with all altitude and/or speed restrictions depicted on the procedure. This term may be used in lieu
of repeating each remaining restriction that appears on the procedure.
COMPOSITE FLIGHT PLAN
A flight plan which specifies VFR operation for one portion of flight and IFR for another portion. It is
used primarily in military operations. (Refer to
AIM.)
COMPULSORY REPORTING POINTS
Reporting points which must be reported to ATC. They are designated on aeronautical charts by solid
triangles or filed in a flight plan as fixes selected to define direct routes. These points are geographical
locations which are defined by navigation aids/fixes. Pilots should discontinue position reporting over
compulsory reporting points when informed by ATC that their aircraft is in "radar contact."
COMPUTER NAVIGATION FIX (CNF)
A Computer Navigation Fix is a point defined by a latitude/longitude coordinate and is required to support
Performance-Based Navigation (PBN) operations. A five-letter identifier denoting a CNF can be found next to
an "x" on en route charts and on some approach charts. Eventually, all CNFs will be labeled and begin with
the letters "CF" followed by three consonants (e.g., 'CFWBG'). CNFs are not recognized by ATC, are not
contained in ATC fix or automation databases, and are not used for ATC purposes. Pilots should not use CNFs
for point-to-point navigation (e.g., proceed direct), filing a flight plan, or in aircraft/ATC
communications. Use of CNFs has not been adopted or recognized by the International Civil Aviation
Organization (ICAO). (Refer to
AIM
1-1-17b5(i)(2), Global Positioning System (GPS).
CONDITIONS NOT MONITORED
When an airport operator cannot monitor the condition of the movement area or airfield surface area, this
information is issued as a NOTAM. Usually necessitated due to staffing, operating hours or other mitigating
factors associated with airport operations.
CONFIDENCE MANEUVER
A confidence maneuver consists of one or more turns, a climb or descent, or other maneuver to determine if
the pilot in command (PIC) is able to receive and comply with ATC instructions.
CONFLICT ALERT
A function of certain air traffic control automated systems designed to alert radar controllers to existing
or pending situations between tracked targets (known IFR or VFR aircraft) that require his/her immediate
attention/action. (See MODE C INTRUDER ALERT.)
CONFLICT RESOLUTION
The resolution of potential conflictions between aircraft that are radar identified and in communication
with ATC by ensuring that radar targets do not touch. Pertinent traffic advisories shall be issued when this
procedure is applied. Note: This procedure shall not be provided utilizing mosaic radar systems.
CONFORMANCE
The condition established when an aircraft's actual position is within the conformance region constructed
around that aircraft at its position, according to the trajectory associated with the aircraft's Current
Plan.
CONFORMANCE REGION
A volume, bounded laterally, vertically, and longitudinally, within which an aircraft must be at a given
time in order to be in conformance with the Current Plan Trajectory for that aircraft. At a given time, the
conformance region is determined by the simultaneous application of the lateral, vertical, and longitudinal
conformance bounds for the aircraft at the position defined by time and aircraft's trajectory.
CONSOLAN
A low frequency, long-distance NAVAID used principally for transoceanic navigations.
CONSOLIDATED WAKE TURBULENCE (CWT)
A version of RECAT that has nine categories, A through I, that refines the grouping of aircraft while
optimizing wake turbulence separation.
CONSTRAINT SATISFACTION POINT (CSP)
Meter Reference Elements (MREs) that are actively scheduled by TBFM. Constraint satisfaction occurs when the
Scheduled Time of Arrival generated for each metered flight conforms to all the scheduling constraints
specified at all the applicable CSPs.
CONTACT
Establish communication with (followed by the name of the facility and, if appropriate, the frequency to
be used).
A flight condition wherein the pilot ascertains the attitude of his/her aircraft and navigates by visual
reference to the surface.
An approach wherein an aircraft on an IFR flight plan, having an air traffic control authorization,
operating clear of clouds with at least 1 mile flight visibility and a reasonable expectation of continuing
to the destination airport in those conditions, may deviate from the instrument approach procedure and
proceed to the destination airport by visual reference to the surface. This approach will only be authorized
when requested by the pilot and the reported ground visibility at the destination airport is at least 1
statute mile. (Refer to
AIM.)
CONTAMINATED RUNWAY
A runway is considered contaminated whenever standing water, ice, snow, slush, frost in any form, heavy
rubber, or other substances are present. A runway is contaminated with respect to rubber deposits or other
friction-degrading substances when the average friction value for any 500-foot segment of the runway within
the ALD fails below the recommended minimum friction level and the average friction value in the adjacent
500-foot segments falls below the maintenance planning friction level.
CONTERMINOUS U.S.
The 48 adjoining States and the District of Columbia.
CONTINENTAL UNITED STATES
The 49 States located on the continent of North America and the District of Columbia.
When used as a control instruction should be followed by another word or words clarifying what is expected
of the pilot. Example: "continue taxi," "continue descent," "continue inbound," etc.
CONTROL AREA [ICAO]
A controlled airspace extending upwards from a specified limit above the earth.
CONTROL SECTOR
An airspace area of defined horizontal and vertical dimensions for which a controller or group of
controllers has air traffic control responsibility, normally within an air route traffic control center or
an approach control facility. Sectors are established based on predominant traffic flows, altitude strata,
and controller workload. Pilot-communications during operations within a sector are normally maintained on
discrete frequencies assigned to the sector. (See DISCRETE FREQUENCY.)
CONTROL SLASH
A radar beacon slash representing the actual position of the associated aircraft. Normally, the control
slash is the one closest to the interrogating radar beacon site. When ARTCC radar is operating in narrowband
(digitized) mode, the control slash is converted to a target symbol.
CONTROLLED AIRSPACE
An airspace of defined dimensions within which air traffic control service is provided to IFR flights and to
VFR flights in accordance with the airspace classification.
Controlled airspace is a generic term that covers Class A, Class B, Class C, Class D, and Class E
airspace.
Controlled airspace is also that airspace within which all aircraft operators are subject to certain
pilot qualifications, operating rules, and equipment requirements in
14 CFR Part 91 (for specific operating
requirements, please refer to
14 CFR Part 91). For IFR operations in any
class of controlled airspace, a pilot must file an IFR flight plan and receive an appropriate ATC
clearance. Each Class B, Class C, and Class D airspace area designated for an airport contains at least
one primary airport around which the airspace is designated (for specific designations and descriptions
of the airspace classes, please refer to
14 CFR Part 71).
Controlled airspace in the United States is designated as follows:
CLASS A Generally, that airspace from 18,000 feet MSL up to and including FL 600, including
the airspace overlying the waters within 12 nautical miles of the coast of the 48 contiguous States
and Alaska. Unless otherwise authorized, all persons must operate their aircraft under IFR.
CLASS B Generally, that airspace from the surface to 10,000 feet MSL surrounding the
nation's busiest airports in terms of airport operations or passenger enplanements. The
configuration of each Class B airspace area is individually tailored and consists of a surface area
and two or more layers (some Class B airspaces areas resemble upside-down wedding cakes), and is
designed to contain all published instrument procedures once an aircraft enters the airspace. An ATC
clearance is required for all aircraft to operate in the area, and all aircraft that are so cleared
receive separation services within the airspace. The cloud clearance requirement for VFR operations
is "clear of clouds."
CLASS C Generally, that airspace from the surface to 4,000 feet above the airport elevation
(charted in MSL) surrounding those airports that have an operational control tower, are serviced by
a radar approach control, and that have a certain number of IFR operations or passenger
enplanements. Although the configuration of each Class C area is individually tailored, the airspace
usually consists of a surface area with a 5 NM radius, a circle with a 10NM radius that extends no
lower than 1,200 feet up to 4,000 feet above the airport elevation and an outer area that is not
charted. Each person must establish two-way radio communications with the ATC facility providing air
traffic services prior to entering the airspace and thereafter maintain those communications while
within the airspace. VFR aircraft are only separated from IFR aircraft within the airspace. (See OUTER AREA.)
CLASS D Generally, that airspace from the surface to 2,500 feet above the airport elevation
(charted in MSL) surrounding those airports that have an operational control tower. The
configuration of each Class D airspace area is individually tailored and when instrument procedures
are published, the airspace will normally be designed to contain the procedures. Arrival extensions
for instrument approach procedures may be Class D or Class E airspace. Unless otherwise authorized,
each person must establish two-way radio communications with the ATC facility providing air traffic
services prior to entering the airspace and thereafter maintain those communications while in the
airspace. No separation services are provided to VFR aircraft.
CLASS E Generally, if the airspace is not Class A, Class B, Class C, or Class D, and it is
controlled airspace, it is Class E airspace. Class E airspace extends upward from either the surface
or a designated altitude to the overlying or adjacent controlled airspace. When designated as a
surface area, the airspace will be configured to contain all instrument procedures. Also in this
class are Federal airways, airspace beginning at either 700 or 1,200 feet AGL used to transition
to/from the terminal or en route environment, en route domestic, and offshore airspace areas
designated below 18,000 feet MSL. Unless designated at a lower altitude, Class E airspace begins at
14,500 MSL over the United States, including that airspace overlying the waters within 12 nautical
miles of the coast of the 48 contiguous States and Alaska, up to, but not including 18,000 feet MSL,
and the airspace above FL 600.
[ICAO] An airspace of defined dimensions within which air traffic control service is provided to IFR flights
and to VFR flights in accordance with the airspace classification. Note: Controlled airspace is a generic
term which covers ATS airspace Classes A, B, C, D, and E.
CONTROLLED TIME OF ARRIVAL
Arrival time assigned during a Traffic Management Program. This time may be modified due to adjustments or
user options.
[ICAO] A person authorized to provide air traffic control services.
CONTROLLER PILOT DATA LINK COMMUNICATIONS (CPDLC)
A two-way digital communications system that conveys textual air traffic control messages between
controllers and pilots using ground or satellite-based radio relay stations.
CONVECTIVE SIGMET
A weather advisory concerning convective weather significant to the safety of all aircraft. Convective
SIGMETs are issued for tornadoes, lines of thunderstorms, embedded thunderstorms of any intensity level,
areas of thunderstorms greater than or equal to VIP level 4 with an area coverage of 4/10 (40%) or more, and
hail 3/4 inch or greater. (See AIRMET.) (See CWA.) (See GRAPHICAL AIRMEN'S
METEOROLOGICAL INFORMATION.) (See
SAW.) (See SIGMET.) (Refer to
AIM.)
The intersection of lines of reference, usually expressed in degrees/minutes/ seconds of latitude and
longitude, used to determine position or location.
COORDINATION FIX
The fix in relation to which facilities will handoff, transfer control of an aircraft, or coordinate flight
progress data. For terminal facilities, it may also serve as a clearance for arriving aircraft.
An error has been made in the transmission and the correct version follows.
COUPLED APPROACH
An instrument approach performed by the aircraft autopilot, and/or visually depicted on the flight director,
which is receiving position information and/or steering commands from onboard navigational equipment. In
general, coupled non-precision approaches must be flown manually (autopilot disengaged) at altitudes lower
than 50 feet AGL below the minimum descent altitude, and coupled precision approaches must be flown manually
(autopilot disengaged) below 50 feet AGL unless authorized to conduct autoland operations. Coupled
instrument approaches are commonly flown to the allowable IFR weather minima established by the operator or
PIC, or flown VFR for training and safety.
COUPLED SCHEDULING (CS)/EXTENDED METERING (XM)
Adds additional Constraint Satisfaction Points for metered aircraft along their route. This provides the
ability to merge flows upstream from the meter fix and results in a more optimal distribution of delays over
a greater distance from the airport, increased meter list accuracy, and more accurate delivery to the meter
fix.
COURSE
The intended direction of flight in the horizontal plane measured in degrees from north.
The ILS localizer signal pattern usually specified as the front course or the back course.
A person assigned to perform an operational duty. A UAS crewmember includes the remote pilot in command, the
person manipulating the controls, and visual observers but may also include other persons as appropriate or
required to ensure the safe operation of the UAS (e.g., sensor operator, ground control station operator).
CRITICAL ENGINE
The engine which, upon failure, would most adversely affect the performance or handling qualities of an
aircraft.
CROSS (FIX) AT (ALTITUDE)
Used by ATC when a specific altitude restriction at a specified fix is required.
CROSS (FIX) AT OR ABOVE (ALTITUDE)
Used by ATC when an altitude restriction at a specified fix is required. It does not prohibit the aircraft
from crossing the fix at a higher altitude than specified; however, the higher altitude may not be one that
will violate a succeeding altitude restriction or altitude assignment. (See
ALTITUDE RESTRICTION.) (Refer to
AIM.)
CROSS (FIX) AT OR BELOW (ALTITUDE)
Used by ATC when a maximum crossing altitude at a specific fix is required. It does not prohibit the
aircraft from crossing the fix at a lower altitude; however, it must be at or above the minimum IFR
altitude. (See ALTITUDE RESTRICTION.) (See MINIMUM IFR ALTITUDES.) (Refer to 14 CFR Part 91.)
CROSSWIND
When used concerning the traffic pattern, the word means "crosswind leg." (See
TRAFFIC PATTERN.)
When used concerning wind conditions, the word means a wind not parallel to the runway or the path of an
aircraft.
The wind component measured in knots at 90 degrees to the longitudinal axis of the runway.
CRUISE
Used in an ATC clearance to authorize a pilot to conduct flight at any altitude from the minimum IFR
altitude up to and including the altitude specified in the clearance. The pilot may level off at any
intermediate altitude within this block of airspace. Climb/descent within the block is to be made at the
discretion of the pilot. However, once the pilot starts descent and verbally reports leaving an altitude in
the block, he/she may not return to that altitude without additional ATC clearance. Further, it is approval
for the pilot to proceed to and make an approach at destination airport and can be used in conjunction with:
An airport clearance limit at locations with a standard/special instrument approach procedure. The CFRs
require that if an instrument letdown to an airport is necessary, the pilot shall make the letdown in
accordance with a standard/special instrument approach procedure for that airport, or
An airport clearance limit at locations that are within/below/outside controlled airspace and without a
standard/special instrument approach procedure. Such a clearance is
NOT AUTHORIZATION for the pilot to descend under IFR conditions below the applicable
minimum IFR altitude nor does it imply that ATC is exercising control over aircraft in Class G airspace;
however, it provides a means for the aircraft to proceed to destination airport, descend, and land in
accordance with applicable CFRs governing VFR flight operations. Also, this provides search and rescue
protection until such time as the IFR flight plan is closed. (See
INSTRUMENT APPROACH PROCEDURE.)
CRUISE CLIMB
A climb technique employed by aircraft, usually at a constant power setting, resulting in an increase of
altitude as the aircraft weight decreases.
CRUISING ALTITUDE
An altitude or flight level maintained during en route level flight. This is a constant altitude and should
not be confused with a cruise clearance. (See ALTITUDE.) (See ICAO term
CRUISING LEVEL.)
An EDCT time generated by the ATCSCC to regulate traffic at arrival airports. Normally, a CT message is
automatically transferred from the traffic management system computer to the NAS en route computer and
appears as an EDCT. In the event of a communication failure between the traffic management system computer
and the NAS, the CT message can be manually entered by the TMC at the en route facility.
Dead reckoning, as applied to flying, is the navigation of an airplane solely by means of computations based
on airspeed, course, heading, wind direction, and speed, groundspeed, and elapsed time.
DEBRIS RESPONSE AREA (DRA)
Used by ATC. Areas of airspace that may be activated in response to unplanned falling debris in the NAS.
DECISION ALTITUDE/DECISION HEIGHT [ICAO Annex 6]
A specified altitude or height (A/H) in the precision approach at which a missed approach must be initiated
if the required visual reference to continue the approach has not been established.
Decision altitude (DA) is referenced to mean sea level and decision height (DH) is referenced to the
threshold elevation.
Category II and III minima are expressed as a DH and not a DA. Minima is assessed by reference to a
radio altimeter and not a barometric altimeter, which makes the minima a DH.
The required visual reference means that section of the visual aids or of the approach area which should
have been in view for sufficient time for the pilot to have made an assessment of the aircraft position
and rate of change of position, in relation to the desired flight path.
DECISION ALTITUDE (DA)
A specified altitude (mean sea level (MSL)) on an instrument approach procedure (ILS, GLS, vertically guided
RNAV) at which the pilot must decide whether to continue the approach or initiate an immediate missed
approach if the pilot does not see the required visual references.
DECISION HEIGHT
With respect to the operation of aircraft, means the height at which a decision must be made during an ILS
or PAR instrument approach to either continue the approach or to execute a missed approach. (See ICAO term
DECISION ALTITUDE/DECISION HEIGHT.)
DECODER
The device used to decipher signals received from ATCRBS transponders to effect their display as select
codes. (See CODES.) (See RADAR.)
DEFENSE AREA
Any airspace of the contiguous United States that is not an ADIZ in which the control of aircraft is
required for reasons of national security.
Delays are distributed to aircraft based on the traffic management program parameters. The delay assignment
is calculated in 15 minute increments and appears as a table in Traffic Flow Management System (TFMS).
DELAY COUNTDOWN TIMER (DCT)
The display of the delay that must be absorbed by a flight prior to crossing a Meter Reference Element (MRE)
to meet the TBFM Scheduled Time of Arrival (STA). It is calculated by taking the difference between the
frozen STA and the Estimated Time of Arrival (ETA).
DELAY INDEFINITE (REASON IF KNOWN) EXPECT FURTHER CLEARANCE (TIME)
Used by ATC to inform a pilot when an accurate estimate of the delay time and the reason for the delay
cannot immediately be determined; e.g., a disabled aircraft on the runway, terminal or center area
saturation, weather below landing minimums, etc. (See
EXPECT FURTHER CLEARANCE (TIME).)
DEPARTURE CENTER
The ARTCC having jurisdiction for the airspace that generates a flight to the impacted airport.
DEPARTURE CONTROL
A function of an approach control facility providing air traffic control service for departing IFR and,
under certain conditions, VFR aircraft. (See APPROACH CONTROL
FACILITY.) (Refer to
AIM.)
DEPARTURE SEQUENCING PROGRAM
A program designed to assist in achieving a specified interval over a common point for departures.
DEPARTURE TIME
The time an aircraft becomes airborne.
DEPARTURE VIEWER
A capability within the Traffic Flow Management System (TFMS) that provides combined displays for monitoring
departure by fixes and departure airports. Traffic management personnel can customize the displays by
selecting the departure airports and fixes of interest. The information displayed is the demand for the
resource (fix or departure airport) in time bins with the flight list and a flight history for one flight at
a time. From the display, flights can be selected for route amendment, one or more at a time, and the Route
Amendment Dialogue (RAD) screen automatically opens for easy route selection and execution. Reroute options
are based on Coded Departure Route (CDR) database and Trajectory Options Set (TOS) (when available).
DESCEND VIA
An abbreviated ATC clearance that requires compliance with a published procedure lateral path and associated
speed restrictions and provides a pilot-discretion descent to comply with published altitude restrictions.
DESCENT SPEED ADJUSTMENTS
Speed deceleration calculations made to determine an accurate VTA. These calculations start at the
transition point and use arrival speed segments to the vertex.
DESIGNATED COMMON TRAFFIC ADVISORY FREQUENCY (CTAF) AREA
In Alaska, in addition to being designated for the purpose of carrying out airport advisory practices while
operating to or from an airport without an operating airport traffic control tower, a CTAF may also be
designated for the purpose of carrying out advisory practices for operations in and through areas with a
high volume of VFR traffic.
DESIRED COURSE
True A predetermined desired course direction to be followed (measured in degrees from true
north).
Magnetic A predetermined desired course direction to be followed (measured in degrees from
local magnetic north).
DESIRED TRACK
The planned or intended track between two waypoints. It is measured in degrees from either magnetic or true
north. The instantaneous angle may change from point to point along the great circle track between
waypoints.
DETRESFA (DISTRESS PHASE) [ICAO]
The code word used to designate an emergency phase wherein there is reasonable certainty that an aircraft
and its occupants are threatened by grave and imminent danger or require immediate assistance.
DEVIATIONS
A departure from a current clearance, such as an off course maneuver to avoid weather or turbulence.
Where specifically authorized in the CFRs and requested by the pilot, ATC may permit pilots to deviate
from certain regulations.
DIGITAL-AUTOMATIC TERMINAL INFORMATION SERVICE (D-ATIS)
The service provides text messages to aircraft, airlines, and other users outside the standard reception
range of conventional ATIS via landline and data link communications to the cockpit. Also, the service
provides a computer synthesized voice message that can be transmitted to all aircraft within range of
existing transmitters. The Terminal Data Link System (TDLS) D-ATIS application uses weather inputs from
local automated weather sources or manually entered meteorological data together with preprogrammed menus to
provide standard information to users. Airports with D-ATIS capability are listed in the Chart Supplement
U.S.
DIGITAL TARGET
A computer generated symbol representing an aircraft's position, based on a primary return or radar beacon
reply, shown on a digital display.
DIGITAL TERMINAL AUTOMATION SYSTEM (DTAS)
A system where digital radar and beacon data is presented on digital displays and the operational program
monitors the system performance on a realtime basis.
DIGITIZED TARGET
A computer generated indication shown on an analog radar display resulting from a primary radar return or a
radar beacon reply.
DIRECT
Straight line flight between two navigational aids, fixes, points, or any combination thereof. When used by
pilots in describing off-airway routes, points defining direct route segments become compulsory reporting
points unless the aircraft is under radar contact.
DIRECTLY BEHIND
An aircraft is considered to be operating directly behind when it is following the actual flight path of the
lead aircraft over the surface of the earth except when applying wake turbulence separation criteria.
As used in the Air Traffic Control Radar Beacon System (ATCRBS), any one of the 4096 selectable Mode 3/A
aircraft transponder codes except those ending in zero zero; e.g., discrete codes: 0010, 1201, 2317, 7777;
nondiscrete codes: 0100, 1200, 7700. Nondiscrete codes are normally reserved for radar facilities that are
not equipped with discrete decoding capability and for other purposes such as emergencies (7700), VFR
aircraft (1200), etc. (See RADAR.) (Refer to
AIM.)
DISCRETE FREQUENCY
A separate radio frequency for use in direct pilot-controller communications in air traffic control which
reduces frequency congestion by controlling the number of aircraft operating on a particular frequency at
one time. Discrete frequencies are normally designated for each control sector in en route/terminal ATC
facilities. Discrete frequencies are listed in the Chart Supplement U.S. and the DOD FLIP IFR En Route
Supplement. (See CONTROL SECTOR.)
DISPLACED THRESHOLD
A threshold that is located at a point on the runway other than the designated beginning of the runway. (See THRESHOLD.) (Refer to
AIM.)
DISTANCE MEASURING EQUIPMENT (DME)
Equipment (airborne and ground) used to measure, in nautical miles, the slant range distance of an aircraft
from the DME navigational aid. (See TACAN .) (See VORTAC.)
DISTRESS
A condition of being threatened by serious and/or imminent danger and of requiring immediate assistance.
In a radar environment, that area in which a prescribed departure route is not required as the only suitable
route to avoid obstacles. The area in which random radar vectors below the MVA/MIA, established in
accordance with the TERPS criteria for diverse departures, obstacles and terrain avoidance, may be issued to
departing aircraft.
DIVERSION (DVRSN)
Flights that are required to land at other than their original destination for reasons beyond the control of
the pilot/company, e.g. periods of significant weather.
A geographical position determined by reference to a navigational aid which provides distance and azimuth
information. It is defined by a specific distance in nautical miles and a radial, azimuth, or course (i.e.,
localizer) in degrees magnetic from that aid. (See DISTANCE MEASURING
EQUIPMENT.) (See FIX.)
DME SEPARATION
Spacing of aircraft in terms of distances (nautical miles) determined by reference to distance measuring
equipment (DME). (See DISTANCE MEASURING EQUIPMENT.)
DOD FLIP
Department of Defense Flight Information Publications used for flight planning, en route, and terminal
operations. FLIP is produced by the National Geospatial Intelligence Agency (NGA) for world-wide use. United
States Government Flight Information Publications (en route charts and instrument approach procedure charts)
are incorporated in DOD FLIP for use in the National Airspace System (NAS).
DOMESTIC AIRSPACE
Airspace which overlies the continental land mass of the United States plus Hawaii and U.S. possessions.
Domestic airspace extends to 12 miles offshore.
DOMESTIC NOTICE
A special notice or notice containing graphics or plain language text pertaining to almost every aspect of
aviation, such as military training areas, large scale sporting events, air show information, Special
Traffic Management Programs (STMPs), and airport-specific information. These notices are applicable to
operations within the United States and can be found on the Domestic Notices website.
DOWNBURST
A strong downdraft which induces an outburst of damaging winds on or near the ground. Damaging winds, either
straight or curved, are highly divergent. The sizes of downbursts vary from 1/2 mile or less to more than 10
miles. An intense downburst often causes widespread damage. Damaging winds, lasting 5 to 30 minutes, could
reach speeds as high as 120 knots.
A parachute device installed on certain aircraft which is deployed on landing roll to assist in deceleration
of the aircraft.
DROP ZONE
Any pre-determined area upon which parachutists or objects land after making an intentional parachute jump
or drop. (Refer to 14 CFR §105.3, Definitions.)
A flight plan filed for a VFR aircraft which intends to operate in airspace within which the ready
identification, location, and control of aircraft are required in the interest of national security.
An EDST notification that an ADR/ADAR/AAR has been applied to the flight plan. Within the route field,
sub-fields consisting of an adapted route or an embedded change in the route are color-coded in cyan with cyan
brackets around the sub-field.
(See EN ROUTE DECISION SUPPORT TOOL.)
EMERGENCY
A distress or an urgency condition.
EMERGENCY AUTOLAND SYSTEM
This system, if activated, will determine an optimal airport, plot a course, broadcast the aircraft's
intentions, fly to the airport, land, and (depending on the model) shut down the engines. Though the system
will broadcast the aircraft's intentions, the controller should assume that transmissions to the aircraft
will not be acknowledged.
EMERGENCY DESCENT MODE
This automated system senses conditions conducive to hypoxia (cabin depressurization). If an aircraft is
equipped and the system is activated, it is designed to turn the aircraft up to 90 degrees, then descend to
a lower altitude and level off, giving the pilot(s) time to recover.
EMERGENCY LOCATOR TRANSMITTER
A radio transmitter attached to the aircraft structure which operates from its own power source on 121.5 MHz
and 243.0 MHz. It aids in locating downed aircraft by radiating a downward sweeping audio tone, 2-4 times
per second. It is designed to function without human action after an accident. (Refer to
14 CFR Part 91.) (Refer to
AIM.)
An EFVS is an installed aircraft system which uses an electronic means to provide a display of the forward
external scene topography (the natural or man-made features of a place or region especially in a way to show
their relative positions and elevation) through the use of imaging sensors, including but not limited to
forward-looking infrared, millimeter wave radiometry, millimeter wave radar, or low-light level image
intensification. An EFVS includes the display element, sensors, computers and power supplies, indications,
and controls. An operator's authorization to conduct an EFVS operation may have provisions which allow
pilots to conduct IAPs when the reported weather is below minimums prescribed on the IAP to be flown.
EN ROUTE AIR TRAFFIC CONTROL SERVICES
Air traffic control service provided aircraft on IFR flight plans, generally by centers, when these aircraft
are operating between departure and destination terminal areas. When equipment, capabilities, and controller
workload permit, certain advisory/assistance services may be provided to VFR aircraft. (See AIR ROUTE TRAFFIC CONTROL CENTER.) (Refer to
AIM.)
EN ROUTE AUTOMATION SYSTEM (EAS)
The complex integrated environment consisting of situation display systems, surveillance systems and flight
data processing, remote devices, decision support tools, and the related communications equipment that form
the heart of the automated IFR air traffic control system. It interfaces with automated terminal systems and
is used in the control of en route IFR aircraft. (Refer to
AIM.)
An automated tool provided at each Radar Associate position in selected En Route facilities. This tool
utilizes flight and radar data to determine present and future trajectories for all active and proposal
aircraft and provides enhanced automated flight data management.
EN ROUTE DESCENT
Descent from the en route cruising altitude which takes place along the route of flight.
A function of the EAS that aids the controller by providing an alert when a tracked aircraft is below or
predicted by the computer to go below a predetermined minimum IFR altitude (MIA).
To be stable or fixed at an altitude or on a course, route, route segment, heading, instrument approach or
departure procedure, etc.
ESTABLISHED ON RNP (EoR) CONCEPT
A system of authorized instrument approaches, ATC procedures, surveillance, and communication requirements
that allow aircraft operations to be safely conducted with approved reduced separation criteria once
aircraft are established on a PBN segment of a published instrument flight procedure.
ESTIMATED (EST)
When used in NOTAMs "EST" is a contraction that is used by the issuing authority only when the condition is
expected to return to service prior to the expiration time. Using "EST" lets the user know that this NOTAM
has the possibility of returning to service earlier than the expiration time. Any NOTAM which includes an
"EST" will be auto expired at the designated expiration time.
ESTIMATED ELAPSED TIME [ICAO]
The estimated time required to proceed from one significant point to another. (See ICAO Term
TOTAL ESTIMATED ELAPSED TIME.)
ESTIMATED OFF-BLOCK TIME [ICAO]
The estimated time at which the aircraft will commence movement associated with departure.
Instructions issued to a pilot making an instrument approach which means continue inbound to the missed
approach point and execute the missed approach procedure as described on the Instrument Approach Procedure
Chart or as previously assigned by ATC. The pilot may climb immediately to the altitude specified in the
missed approach procedure upon making a missed approach. No turns should be initiated prior to reaching the
missed approach point. When conducting an ASR or PAR approach, execute the assigned missed approach
procedure immediately upon receiving instructions to "execute missed approach." (Refer to
AIM.)
EXPECT (ALTITUDE) AT (TIME) or (FIX)
Used under certain conditions to provide a pilot with an altitude to be used in the event of two-way
communications failure. It also provides altitude information to assist the pilot in planning. (Refer to
AIM.)
EXPECT DEPARTURE CLEARANCE TIME (EDCT)
The runway release time assigned to an aircraft in a traffic management program and shown on the flight
progress strip as an EDCT. (See GROUND DELAY PROGRAM.)
EXPECT FURTHER CLEARANCE (TIME)
The time a pilot can expect to receive clearance beyond a clearance limit.
EXPECT FURTHER CLEARANCE VIA (AIRWAYS, ROUTES OR FIXES)
Used to inform a pilot of the routing he/she can expect if any part of the route beyond a short range
clearance limit differs from that filed.
EXPEDITE
Used by ATC when prompt compliance is required to avoid the development of an imminent situation. Expedite
climb/descent normally indicates to a pilot that the approximate best rate of climb/descent should be used
without requiring an exceptional change in aircraft handling characteristics.
F
FAA-RECOGNIZED IDENTIFICATION AREA (FRIA)
A defined geographic area where persons can operate UAS without remote identification, provided they
maintain visual line of sight.
Remains of fallen members of the United States military are often returned home by aircraft. These flights
may be identified with the phrase "FALLEN HERO" added to the remarks section of the flight plan, or they may
be transmitted via air/ground communications. If able, these flights will receive priority handling.
FAST FILE
An FSS system whereby a pilot files a flight plan via telephone that is recorded and later transcribed for
transmission to the appropriate air traffic facility. (Alaska only.)
FAWP
Final Approach Waypoint
FEATHERED PROPELLER
A propeller whose blades have been rotated so that the leading and trailing edges are nearly parallel with
the aircraft flight path to stop or minimize drag and engine rotation. Normally used to indicate shutdown of
a reciprocating or turboprop engine due to malfunction.
The fix depicted on Instrument Approach Procedure Charts which establishes the starting point of the feeder
route.
FEEDER ROUTE
A route depicted on instrument approach procedure charts to designate routes for aircraft to proceed from
the en route structure to the initial approach fix (IAF). (See
INSTRUMENT APPROACH PROCEDURE.)
FERRY FLIGHT
A flight for the purpose of:
Returning an aircraft to base.
Delivering an aircraft from one location to another.
Moving an aircraft to and from a maintenance base. Ferry flights, under certain conditions, may be
conducted under terms of a special flight permit.
That part of an instrument approach procedure which commences at the specified final approach fix or point,
or where such a fix or point is not specified.
At the end of the last procedure turn, base turn or inbound turn of a racetrack procedure, if specified;
or
At the point of interception of the last track specified in the approach procedure; and ends at a point
in the vicinity of an aerodrome from which:
A landing can be made; or
A missed approach procedure is initiated.
FINAL APPROACH COURSE
A bearing/radial/track of an instrument approach leading to a runway or an extended runway centerline all
without regard to distance.
FINAL APPROACH FIX
The fix from which the final approach (IFR) to an airport is executed and which identifies the beginning of
the final approach segment. It is designated on Government charts by the Maltese Cross symbol for
nonprecision approaches and the lightning bolt symbol, designating the PFAF, for precision approaches; or
when ATC directs a lower-than-published glideslope/path or vertical path intercept altitude, it is the
resultant actual point of the glideslope/path or vertical path intercept. (See
FINAL APPROACH POINT.) (See GLIDESLOPE INTERCEPT ALTITUDE.)
(See SEGMENTS OF AN INSTRUMENT APPROACH
PROCEDURE.)
The point, applicable only to a nonprecision approach with no depicted FAF (such as an on airport VOR),
where the aircraft is established inbound on the final approach course from the procedure turn and where the
final approach descent may be commenced. The FAP serves as the FAF and identifies the beginning of the final
approach segment. (See FINAL APPROACH FIX.) (See SEGMENTS OF AN INSTRUMENT APPROACH PROCEDURE.)
[ICAO] That segment of an instrument approach procedure in which alignment and descent for landing are
accomplished.
FINAL CONTROLLER
The controller providing information and final approach guidance during PAR and ASR approaches utilizing
radar equipment. (See RADAR APPROACH.)
FINAL GUARD SERVICE
A value added service provided in conjunction with LAA/RAA only during periods of significant and fast
changing weather conditions that may affect landing and takeoff operations.
FINAL MONITOR AID
A high resolution color display that is equipped with the controller alert system hardware/software used to
monitor the no transgression zone (NTZ) during simultaneous parallel approach operations. The display
includes alert algorithms providing the target predictors, a color change alert when a target penetrates or
is predicted to penetrate the no transgression zone (NTZ), synthesized voice alerts, and digital mapping.
(See RADAR APPROACH.)
FINAL MONITOR CONTROLLER
Air Traffic Control Specialist assigned to radar monitor the flight path of aircraft during simultaneous
parallel (approach courses spaced less than 9000 feet/9200 feet above 5000 feet) and simultaneous close
parallel approach operations. Each runway is assigned a final monitor controller during simultaneous
parallel and simultaneous close parallel ILS approaches.
A geographical position determined by visual reference to the surface, by reference to one or more radio
NAVAIDs, by celestial plotting, or by another navigational device.
FIX BALANCING
A process whereby aircraft are evenly distributed over several available arrival fixes reducing delays and
controller workload.
FLAG
A warning device incorporated in certain airborne navigation and flight instruments indicating that:
Instruments are inoperative or otherwise not operating satisfactorily, or
Signal strength or quality of the received signal falls below acceptable values.
An emergency condition caused by a loss of engine power.
FLAMEOUT PATTERN
An approach normally conducted by a single-engine military aircraft experiencing loss or anticipating loss
of engine power or control. The standard overhead approach starts at a relatively high altitude over a
runway ("high key") followed by a continuous 180 degree turn to a high, wide position ("low key") followed
by a continuous 180 degree turn final. The standard straight-in pattern starts at a point that results in a
straight-in approach with a high rate of descent to the runway. Flameout approaches terminate in the type
approach requested by the pilot (normally fullstop).
FLIGHT CHECK
A call-sign prefix used by FAA aircraft engaged in flight inspection/certification of navigational aids and
flight procedures. The word "recorded" may be added as a suffix; e.g., "Flight Check 320 recorded" to
indicate that an automated flight inspection is in progress in terminal areas. (See FLIGHT INSPECTION.) (Refer to
AIM.)
An airspace of defined dimensions within which Flight Information Service and Alerting Service are provided.
Flight Information Service. A service provided for the purpose of giving advice and information useful
for the safe and efficient conduct of flights.
Alerting Service. A service provided to notify appropriate organizations regarding aircraft in need of
search and rescue aid and to assist such organizations as required.
FLIGHT INFORMATION SERVICE
A service provided for the purpose of giving advice and information useful for the safe and efficient
conduct of flights.
FLIGHT INFORMATION SERVICE BROADCAST (FISB)
A ground broadcast service provided through the ADSB Broadcast Services network over the UAT data link that
operates on 978 MHz. The FISB system provides pilots and flight crews of properly equipped aircraft with a
cockpit display of certain aviation weather and aeronautical information.
FLIGHT INSPECTION
Inflight investigation and evaluation of a navigational aid to determine whether it meets established
tolerances. (See FLIGHT CHECK.) (See NAVIGATIONAL
AID.)
FLIGHT LEVEL
A level of constant atmospheric pressure related to a reference datum of 29.92 inches of mercury. Each is
stated in three digits that represent hundreds of feet. For example, flight level (FL) 250 represents a
barometric altimeter indication of 25,000 feet; FL 255, an indication of 25,500 feet. (See ICAO term
FLIGHT LEVEL.)
[ICAO] A surface of constant atmospheric pressure which is related to a specific pressure datum, 1013.2 hPa
(1013.2 mb), and is separated from other such surfaces by specific pressure intervals.
Note 1: A pressure type altimeter calibrated in accordance with the standard atmosphere:
When set to a QNH altimeter setting, will indicate altitude;
When set to a QFE altimeter setting, will indicate height above the QFE reference datum; and
When set to a pressure of 1013.2 hPa (1013.2 mb), may be used to indicate flight levels.
Note 2: The terms 'height' and 'altitude,' used in Note 1 above, indicate altimetric rather than
geometric heights and altitudes.
FLIGHT LINE
A term used to describe the precise movement of a civil photogrammetric aircraft along a predetermined
course(s) at a predetermined altitude during the actual photographic run.
FLIGHT MANAGEMENT SYSTEMS
A computer system that uses a large data base to allow routes to be preprogrammed and fed into the system by
means of a data loader. The system is constantly updated with respect to position accuracy by reference to
conventional navigation aids. The sophisticated program and its associated data base ensures that the most
appropriate aids are automatically selected during the information update cycle.
FLIGHT PATH
A line, course, or track along which an aircraft is flying or intended to be flown. (See
COURSE.) (See TRACK.)
FLIGHT PLAN
Specified information relating to the intended flight of an aircraft that is filed electronically, orally,
or in writing with an FSS, third-party vendor, or an ATC facility. (See FAST FILE.)
(See FILED.) (Refer to
AIM.)
FLIGHT PLAN AREA (FPA)
The geographical area assigned to a flight service station (FSS) for the purpose of establishing primary
responsibility for services that may include search and rescue for VFR aircraft, issuance of NOTAMs, pilot
briefings, inflight services, broadcast services, emergency services, flight data processing, international
operations, and aviation weather services. Large consolidated FSS facilities may combine FPAs into larger
areas of responsibility (AOR). (See FLIGHT SERVICE STATION.) (See TIE-IN FACILITY.)
FLIGHT RECORDER
A general term applied to any instrument or device that records information about the performance of an
aircraft in flight or about conditions encountered in flight. Flight recorders may make records of airspeed,
outside air temperature, vertical acceleration, engine RPM, manifold pressure, and other pertinent variables
for a given flight. (See ICAO term FLIGHT RECORDER.)
[ICAO] Any type of recorder installed in the aircraft for the purpose of complementing accident/incident
investigation. Note: See Annex 6 Part I, for specifications relating to flight recorders.
FLIGHT SERVICE STATION (FSS)
An air traffic facility which provides pilot briefings, flight plan processing, en route flight advisories,
search and rescue services, and assistance to lost aircraft and aircraft in emergency situations. FSS also
relay ATC clearances, process Notices to Air Missions, and broadcast aviation weather and aeronautical
information. In Alaska, FSS provide Airport Advisory Services. (See FLIGHT PLAN
AREA.) (See TIE-IN FACILITY.)
FLIGHT STANDARDS DISTRICT OFFICE
An FAA field office serving an assigned geographical area and staffed with Flight Standards personnel who
serve the aviation industry and the general public on matters relating to the certification and operation of
air carrier and general aviation aircraft. Activities include general surveillance of operational safety,
certification of airmen and aircraft, accident prevention, investigation, enforcement, etc.
FLIGHT TERMINATION
The intentional and deliberate process of terminating the flight of a UA in the event of an unrecoverable
lost link, loss of control, or other failure that compromises the safety of flight.
FLIGHT TEST
A flight for the purpose of:
Investigating the operation/flight characteristics of an aircraft or aircraft component.
Evaluating an applicant for a pilot certificate or rating.
Informs the pilot of the heading he/she should fly. The pilot may have to turn to, or continue on, a
specific compass direction in order to comply with the instructions. The pilot is expected to turn in the
shorter direction to the heading unless otherwise instructed by ATC.
FLY-BY WAYPOINT
A fly-by waypoint requires the use of turn anticipation to avoid overshoot of the next flight segment.
FLY-OVER WAYPOINT
A fly-over waypoint precludes any turn until the waypoint is overflown and is followed by an intercept
maneuver of the next flight segment.
More than one aircraft which, by prior arrangement between the pilots, operate as a single aircraft with
regard to navigation and position reporting. Separation between aircraft within the formation is the
responsibility of the flight leader and the pilots of the other aircraft in the flight. This includes
transition periods when aircraft within the formation are maneuvering to attain separation from each other
to effect individual control and during join-up and breakaway.
A standard formation is one in which a proximity of no more than 1 mile laterally or longitudinally and
within 100 feet vertically from the flight leader is maintained by each wingman.
Nonstandard formations are those operating under any of the following conditions:
When the flight leader has requested and ATC has approved other than standard formation dimensions.
When operating within an authorized altitude reservation (ALTRV) or under the provisions of a letter
of agreement.
Terms used in referring to arrivals which have been assigned ACLTs and to the lists in which they are
displayed.
FREEZE HORIZON
The time or point at which an aircraft's STA becomes fixed and no longer fluctuates with each radar update.
This setting ensures a constant time for each aircraft, necessary for the metering controller to plan
his/her delay technique. This setting can be either in distance from the meter fix or a prescribed flying
time to the meter fix.
FREEZE SPEED PARAMETER
A speed adapted for each aircraft to determine fast and slow aircraft. Fast aircraft freeze on parameter
FCLT and slow aircraft freeze on parameter MLDI.
A measurement of the friction characteristics of the runway pavement surface using continuous self-watering
friction measurement equipment in accordance with the specifications, procedures and schedules contained in
AC 150/532012, Measurement, Construction, and Maintenance of Skid Resistant Airport Pavement Surfaces.
A phrase used by either pilots or controllers when relating to the fuel remaining on board until actual fuel
exhaustion. When transmitting such information in response to either a controller question or pilot
initiated cautionary advisory to air traffic control, pilots will state the APPROXIMATE NUMBER OF MINUTES
the flight can continue with the fuel remaining. All reserve fuel SHOULD BE INCLUDED in the time stated, as
should an allowance for established fuel gauge system error.
FUEL SIPHONING
Unintentional release of fuel caused by overflow, puncture, loose cap, etc.
The combination of all available surveillance sources (airport surveillance radar [ASR], air route
surveillance radar [ARSR], ADS-B, etc.) into the display of a single tracked target for air traffic control
separation services. FUSION is the equivalent of the current single-sensor radar display. FUSION performance
is characteristic of a single-sensor radar display system. Terminal areas use mono-pulse secondary
surveillance radar (ASR 9, Mode S or ASR 11, MSSR).
G
GATE HOLD PROCEDURES
Procedures at selected airports to hold aircraft at the gate or other ground location whenever departure
delays exceed or are anticipated to exceed 15 minutes. The sequence for departure will be maintained in
accordance with initial callup unless modified by flow control restrictions. Pilots should monitor the
ground control/clearance delivery frequency for engine start/taxi advisories or new proposed start/taxi time
if the delay changes.
That portion of civil aviation that does not include scheduled or unscheduled air carriers or commercial
space operations.
[ICAO] All civil aviation operations other than scheduled air services and nonscheduled air transport
operations for remuneration or hire.
GEO MAP
The digitized map markings associated with the ASR-9 Radar System.
GRAPHICAL AIRMEN'S METEOROLOGICAL INFORMATION
A graphical depiction of weather that may be hazardous to aircraft, but are less severe than SIGMETs.
G-AIRMETS are issued 3 hours apart for a period of up to 12 hours into the future for the lower 48 states and
coastal waters. The weather hazards depicted can be:
Provides vertical guidance for aircraft during approach and landing. The glideslope/glidepath is based on
the following:
Electronic components emitting signals which provide vertical guidance by reference to airborne
instruments during instrument approaches such as ILS or
Visual ground aids, such as VASI, which provide vertical guidance for a VFR approach or for the visual
portion of an instrument approach and landing.
PAR. Used by ATC to inform an aircraft making a PAR approach of its vertical position (elevation)
relative to the descent profile.
The published minimum altitude to intercept the glideslope in the intermediate segment of an instrument
approach. Government charts use the lightning bolt symbol to identify this intercept point. This
intersection is called the Precise Final Approach fix (PFAF). ATC directs a higher altitude, the resultant
intercept becomes the PFAF. (See FINAL APPROACH FIX.) (See SEGMENTS OF AN INSTRUMENT APPROACH PROCEDURE.)
GLOBAL NAVIGATION SATELLITE SYSTEM (GNSS)
GNSS refers collectively to the worldwide positioning, navigation, and timing determination capability
available from one or more satellite constellations. A GNSS constellation may be augmented by ground
stations and/or geostationary satellites to improve integrity aEd position accuracy. (See GROUND-BASED AUGMENTATION SYSTEM.) (See SATELLITE-BASED AUGMENTATION SYSTEM.)
GLOBAL NAVIGATION SATELLITE SYSTEM MINIMUM EN ROUTE IFR ALTITUDE (GNSS MEA)
The minimum en route IFR altitude on a published ATS route or route segment which assures acceptable Global
Navigation Satellite System reception and meets obstacle clearance requirements. (Refer to
14 CFR Part 91.) (Refer to
14 CFR Part 95.)
GLOBAL POSITIONING SYSTEM (GPS)
GPS refers to the worldwide positioning, navigation and timing determination capability available from the
U.S. satellite constellation. The service provided by GPS for civil use is defined in the GPS Standard
Positioning System Performance Standard. GPS is composed of space, control, and user elements.
Proceed with your message. Not to be used for any other purpose.
GO AROUND
Instructions for a pilot to abandon his/her approach to landing. Additional instructions may follow. Unless
otherwise advised by ATC, a VFR aircraft or an aircraft conducting visual approach should overfly the runway
while climbing to traffic pattern altitude and enter the traffic pattern via the crosswind leg. A pilot on
an IFR flight plan making an instrument approach should execute the published missed approach procedure or
proceed as instructed by ATC; e.g., "Go around" (additional instructions if required). (See LOW APPROACH.) (See MISSED APPROACH.)
A view available with EDST that provides a graphic display of aircraft, traffic, and notification of
predicted conflicts. Graphic routes for Current Plans and Trial Plans are displayed upon controller request.
(See EN ROUTE DECISION SUPPORT TOOL.)
GROSS NAVIGATION ERROR (GNE)
A lateral deviation of 10 NM or more from the aircraft's cleared route.
GROUND BASED AUGMENTATION SYSTEM (GBAS)
A ground based GNSS station which provides local differential corrections, integrity parameters and approach
data via VHF data broadcast to GNSS users to meet real-time performance requirements for CAT I precision
approaches. The aircraft applies the broadcast data to improve the accuracy and integrity of its GNSS
signals and computes the deviations to the selected approach. A single ground station can serve multiple
runway ends up to an approximate radius of 23 NM.
GROUND BASED AUGMENTATION SYSTEM (GBAS) LANDING SYSTEM (GLS)
A type of precision IAP based on local augmentation of GNSS data using a single GBAS station to transmit
locally corrected GNSS data, integrity parameters and approach information. This improves the accuracy of
aircraft GNSS receivers' signal in space, enabling the pilot to fly a precision approach with much greater
flexibility, reliability and complexity. The GLS procedure is published on standard IAP charts, features the
title GLS with the designated runway and minima as low as 200 feet DA. Future plans are expected to support
Cat II and CAT III operations.
A calculated speed that will allow aircraft to meet the TBFM schedule at en route and TRACON boundary meter
fixes.
GROUND CLUTTER
A pattern produced on the radar scope by ground returns which may degrade other radar returns in the
affected area. The effect of ground clutter is minimized by the use of moving target indicator (MTI)
circuits in the radar equipment resulting in a radar presentation which displays only targets which are in
motion. (See CLUTTER.)
GROUND COMMUNICATION OUTLET (GCO)
An unstaffed, remotely controlled, ground/ground communications facility. Pilots at uncontrolled airports
may contact ATC and FSS via VHF radio to a telephone connection. If the connection goes to ATC, the pilot
can obtain an IFR clearance or close an IFR flight plan. If the connection goes to Flight Service, the pilot
can open or close a VFR flight plan; obtain an updated weather briefing prior to takeoff; close an IFR
flight plan; or, for Alaska or MEDEVAC only, obtain an IFR clearance. Pilots will use four "key clicks" on
the VHF radio to contact the appropriate ATC facility or six "key clicks" to contact the FSS. The GCO system
is intended to be used only on the ground.
GROUND CONTROLLED APPROACH
A radar approach system operated from the ground by air traffic control personnel transmitting instructions
to the pilot by radio. The approach may be conducted with surveillance radar (ASR) only or with both
surveillance and precision approach radar (PAR). Usage of the term "GCA" by pilots is discouraged except
when referring to a GCA facility. Pilots should specifically request a "PAR" approach when a precision radar
approach is desired or request an "ASR" or "surveillance" approach when a nonprecision radar approach is
desired. (See RADAR APPROACH.)
GROUND DELAY PROGRAM (GDP)
A traffic management process administered by the ATCSCC; when aircraft are held on the ground. The purpose
of the program is to support the TM mission and limit airborne holding. It is a flexible program and may be
implemented in various forms depending upon the needs of the AT system. Ground delay programs provide for
equitable assignment of delays to all system users.
GROUND SPEED
The speed of an aircraft relative to the surface of the earth.
GROUND STOP (GS)
The GS is a process that requires aircraft that meet a specific criteria to remain on the ground. The
criteria may be airport specific, airspace specific, or equipment specific; for example, all departures to
San Francisco, or all departures entering Yorktown sector, or all Category I and II aircraft going to
Charlotte. GSs normally occur with little or no warning.
The height above a designated helicopter landing area used for helicopter instrument approach procedures.
(Refer to 14 CFR Part 97.)
HEIGHT ABOVE TOUCHDOWN
The height of the Decision Height or Minimum Descent Altitude above the highest runway elevation in the
touchdown zone (first 3,000 feet of the runway). HAT is published on instrument approach charts in
conjunction with all straight-in minimums. (See DECISION HEIGHT.) (See MINIMUM DESCENT ALTITUDE.)
HANDOFF
An action taken to transfer the radar identification of an aircraft from one controller to another if the
aircraft will enter the receiving controller's airspace and radio communications with the aircraft will be
transferred.
Used by pilots to inform ATC that they have received runway, wind, and altimeter information only.
HAZARDOUS MATERIALS (HAZMAT)
Hazardous materials as defined by 49 Code of Federal Regulations (CFR) §171.8. (Refer to 49 CFR Part 171.8)
(Refer to AIM)
HAZARDOUS WEATHER INFORMATION
Summary of significant meteorological information (SIGMET/WS), convective significant meteorological
information (convective SIGMET/WST), urgent pilot weather reports (urgent PIREP/UUA), center weather
advisories (CWA), airmen's meteorological information (AIRMET/WA), graphical airmen's meteorological
information (G-AIRMET) and any other weather such as isolated thunderstorms that are rapidly developing and
increasing in intensity, or low ceilings and visibilities that are becoming widespread which is considered
significant and are not included in a current hazardous weather advisory.
The height of the Minimum Descent Altitude above the published airport elevation. This is published in
conjunction with circling minimums. (See MINIMUM DESCENT ALTITUDE.)
HELICOPTER
A heavier-than-air aircraft supported in flight chiefly by the reactions of the air on one or more
power-driven rotors on substantially vertical axes.
HELIPAD
A small, designated area, usually with a prepared surface, on a heliport, airport, landing/take-off area,
apron/ramp, or movement area used for takeoff, landing, or parking of helicopters.
HELIPORT
An area of land, water, or structure used or intended to be used for the landing and takeoff of helicopters
and includes its buildings and facilities if any.
HELIPORT REFERENCE POINT (HRP)
The geographic center of a heliport.
HERTZ
The standard radio equivalent of frequency in cycles per second of an electromagnetic wave. Kilohertz (kHz)
is a frequency of one thousand cycles per second. Megahertz (MHz) is a frequency of one million cycles per
second.
A long radius taxiway designed and provided with lighting or marking to define the path of aircraft,
traveling at high speed (up to 60 knots), from the runway center to a point on the center of a taxiway. Also
referred to as long radius exit or turn-off taxiway. The high speed taxiway is designed to expedite aircraft
turning off the runway after landing, thus reducing runway occupancy time.
A surveillance system that provides a sensor update rate of less than 4.8 seconds.
HOLD FOR RELEASE
Used by ATC to delay an aircraft for traffic management reasons; i.e., weather, traffic volume, etc. Hold
for release instructions (including departure delay information) are used to inform a pilot or a controller
(either directly or through an authorized relay) that an IFR departure clearance is not valid until a
release time or additional instructions have been received. (See ICAO term
HOLDING POINT.)
HOLD IN LIEU OF PROCEDURE TURN
A hold in lieu of procedure turn shall be established over a final or intermediate fix when an approach can
be made from a properly aligned holding pattern. The hold in lieu of procedure turn permits the pilot to
align with the final or intermediate segment of the approach and/or descend in the holding pattern to an
altitude that will permit a normal descent to the final approach fix altitude. The hold in lieu of procedure
turn is a required maneuver (the same as a procedure turn) unless the aircraft is being radar vectored to
the final approach course, when "NoPT" is shown on the approach chart, or when the pilot requests or the
controller advises the pilot to make a "straight in" approach.
HOLD PROCEDURE
A predetermined maneuver which keeps aircraft within a specified airspace while awaiting further clearance
from air traffic control. Also used during ground operations to keep aircraft within a specified area or at
a specified point while awaiting further clearance from air traffic control. (See
HOLDING FIX.) (Refer to
AIM.)
HOLDING FIX
A specified fix identifiable to a pilot by NAVAIDs or visual reference to the ground used as a reference
point in establishing and maintaining the position of an aircraft while holding. (See FIX.)
(See VISUAL HOLDING.) (Refer to
AIM.)
HOLDING POINT [ICAO]
A specified location, identified by visual or other means, in the vicinity of which the position of an
aircraft in flight is maintained in accordance with air traffic control clearances.
A point on the runway beyond which a landing aircraft with a LAHSO clearance is not authorized to proceed.
This point may be located prior to an intersecting runway, taxiway, predetermined point, or
approach/departure flight path.
HOLD-SHORT POSITION LIGHTS
Flashing in-pavement white lights located at specified hold-short points.
HOLD-SHORT POSITION MARKING
The painted runway marking located at the hold-short point on all LAHSO runways.
HOLD-SHORT POSITION SIGNS
Red and white holding position signs located alongside the hold-short point.
HOMING
Flight toward a NAVAID, without correcting for wind, by adjusting the aircraft heading to maintain a
relative bearing of zero degrees. (See BEARING.) (See ICAO term
HOMING.)
[ICAO] The procedure of using the direction-finding equipment of one radio station with the emission of
another radio station, where at least one of the stations is mobile, and whereby the mobile station proceeds
continuously towards the other station.
HOT SPOT
A location on an airport movement area with a history of potential risk of collision or runway incursion,
and where heightened attention by pilots/drivers is necessary.
HOVER CHECK
Used to describe when a helicopter/VTOL aircraft requires a stabilized hover to conduct a performance/power
check prior to hover taxi, air taxi, or takeoff. Altitude of the hover will vary based on the purpose of the
check.
HOVER TAXI
Used to describe a helicopter/VTOL aircraft movement conducted above the surface and in ground effect at
airspeeds less than approximately 20 knots. The actual height may vary, and some helicopters may require
hover taxi above 25 feet AGL to reduce ground effect turbulence or provide clearance for cargo slingloads.
(See AIR TAXI.) (See HOVER CHECK.) (Refer to
AIM.)
HOW DO YOU HEAR ME?
A question relating to the quality of the transmission or to determine how well the transmission is being
received.
An ICAO 3LD is an exclusive designator that, when used together with a flight number, becomes the aircraft
call sign and provides distinct aircraft identification to air traffic control (ATC). ICAO approves 3LDs to
enhance the safety and security of the air traffic system. An ICAO 3LD may be assigned to a company, agency,
or organization and is used instead of the aircraft registration number for ATC operational and security
purposes. An ICAO 3LD is also used for aircraft identification in the flight plan and associated messages
and can be used for domestic and international flights. A telephony associated with an ICAO 3LD is used for
radio communication.
ICING
The accumulation of airframe ice. Types of icing are:
Rime Ice: Rough, milky, opaque ice formed by the instantaneous freezing of small supercooled
water droplets.
Clear Ice: A glossy, clear, or translucent ice formed by the relatively slow freezing of large
supercooled water droplets.
Mixed: A mixture of clear ice and rime ice.
Intensity of icing:
Trace: Ice becomes noticeable. The rate of accumulation is slightly greater than the rate of
sublimation. A representative accretion rate for reference purposes is less than ¼ inch (6 mm) per hour
on the outer wing. The pilot should consider exiting the icing conditions before they become worse.
Light: The rate of ice accumulation requires occasional cycling of manual deicing systems to
minimize ice accretions on the airframe. A representative accretion rate for reference purposes is ¼
inch to 1 inch (0.6 to 2.5 cm) per hour on the unprotected part of the outer wing. The pilot should
consider exiting the icing condition.
Moderate: The rate of ice accumulation requires frequent cycling of manual deicing systems to
minimize ice accretions on the airframe. A representative accretion rate for reference purposes is 1 to
3 inches (2.5 to 7.5 cm) per hour on the unprotected part of the outer wing. The pilot should consider
exiting the icing condition as soon as possible.
Severe: The rate of ice accumulation is such that ice protection systems fail to remove the
accumulation of ice and ice accumulates in locations not normally prone to icing, such as areas aft of
protected surfaces and any other areas identified by the manufacturer. A representative accretion rate
for reference purposes is more than 3 inches (7.5 cm) per hour on the unprotected part of the outer
wing. By regulation, immediate exit is required.
Note: Severe icing is aircraft dependent, as are the other categories of icing intensity. Severe icing
may occur at any ice accumulation rate when the icing rate or ice accumulations exceed the tolerance
of the aircraft.
A request for a pilot to activate the aircraft transponder identification feature. This will help the
controller to confirm an aircraft identity or to identify an aircraft. (Refer to
AIM.)
IDENT FEATURE
The special feature in the Air Traffic Control Radar Beacon System (ATCRBS) equipment. It is used to
immediately distinguish one displayed beacon target from other beacon targets. (See
IDENT.)
IDENTIFICATION [ICAO]
The situation which exists when the position indication of a particular aircraft is seen on a situation
display and positively identified.
Routes used by the Department of Defense and associated Reserve and Air Guard units for the purpose of
conducting low-altitude navigation and tactical training in both IFR and VFR weather conditions below 10,000
feet MSL at airspeeds in excess of 250 knots IAS.
IFR TAKEOFF MINIMUMS AND DEPARTURE PROCEDURES
Title 14 Code of Federal Regulations Part 91, prescribes standard takeoff rules for certain civil users. At
some airports, obstructions or other factors require the establishment of nonstandard takeoff minimums,
departure procedures, or both to assist pilots in avoiding obstacles during climb to the minimum en route
altitude. Those airports are listed in FAA/DOD Instrument Approach Procedures (IAPs) Charts under a section
entitled "IFR Takeoff Minimums and Departure Procedures." The FAA/DOD IAP chart legend illustrates the
symbol used to alert the pilot to nonstandard takeoff minimums and departure procedures. When departing IFR
from such airports or from any airports where there are no departure procedures, DPs, or ATC facilities
available, pilots should advise ATC of any departure limitations. Controllers may query a pilot to determine
acceptable departure directions, turns, or headings after takeoff. Pilots should be familiar with the
departure procedures and must assure that their aircraft can meet or exceed any specified climb gradients.
IF/IAWP
Intermediate Fix/Initial Approach Waypoint. The waypoint where the final approach course of a T approach
meets the crossbar of the T. When designated (in conjunction with a TAA) this waypoint will be used as an
IAWP when approaching the airport from certain directions, and as an IFWP when beginning the approach from
another IAWP.
Category I. An ILS approach procedure which provides for approach to a height above touchdown of not
less than 200 feet and with runway visual range of not less than 1,800 feet.
Special Authorization Category I. An ILS approach procedure which provides for approach to a height
above touchdown of not less than 150 feet and with runway visual range of not less than 1,400 feet, HUD
to DH.
Category II. An ILS approach procedure which provides for approach to a height above touchdown of not
less than 100 feet and with runway visual range of not less than 1,200 feet (with autoland or HUD to
touchdown and noted on authorization, RVR 1,000 feet).
Special Authorization Category II with Reduced Lighting. An ILS approach procedure which provides for
approach to a height above touchdown of not less than 100 feet and with runway visual range of not less
than 1,200 feet with autoland or HUD to touchdown and noted on authorization (no touchdown zone and
centerline lighting are required).
Category III:
IIIA: An ILS approach procedure which provides for approach without a decision height minimum and
with runway visual range of not less than 700 feet.
IIIB: An ILS approach procedure which provides for approach without a decision height minimum and
with runway visual range of not less than 150 feet.
IIIC: An ILS approach procedure which provides for approach without a decision height minimum and
without runway visual range minimum.
[ICAO] That segment of an instrument approach procedure between the initial approach fix and the
intermediate approach fix or, where applicable, the final approach fix or point.
INLAND NAVIGATION FACILITY
A navigation aid on a North American Route at which the common route and/or the noncommon route begins or
ends.
INNER MARKER
A marker beacon used with an ILS (CAT II) precision approach located between the middle marker and the end
of the ILS runway, transmitting a radiation pattern keyed at six dots per second and indicating to the
pilot, both aurally and visually, that he/she is at the designated decision height (DH), normally 100 feet
above the touchdown zone elevation, on the ILS CAT II approach. It also marks progress during a CAT III
approach. (See INSTRUMENT LANDING SYSTEM.) (Refer to
AIM.)
An approach and landing using instruments for navigation guidance based on an instrument approach procedure.
There are two methods for executing instrument approach operations:
A two-dimensional (2D) instrument approach operation, using lateral navigation guidance only; and
A three-dimensional(3D)instrument approach operation, using both lateral and vertical navigation
guidance.
Note:Lateral and vertical navigation guidance refers to the guidance provided either by:
a ground-based radio navigation aid; or
computer-generated navigation data fromground-based, space-based, self-contained navigation aids or a
combination of these.
A series of predetermined maneuvers for the orderly transfer of an aircraft under instrument flight
conditions from the beginning of the initial approach to a landing or to a point from which a landing may be
made visually. It is prescribed and approved for a specific airport by competent authority. (See SEGMENTS OF AN INSTRUMENT APPROACH PROCEDURE.)
(Refer to 14 CFR Part 91.) (Refer to
AIM.)
U.S. civil standard instrument approach procedures are approved by the FAA as prescribed under
14 CFR Part 97 and are available for
public use.
U.S. military standard instrument approach procedures are approved and published by the Department of
Defense.
Special instrument approach procedures are approved by the FAA for individual operators but are not
published in 14 CFR Part 97 for public
use.
[ICAO] A series of predetermined maneuvers by reference to flight instruments with specified protection from
obstacles from the initial approach fix, or where applicable, from the beginning of a defined arrival route
to a point from which a landing can be completed and thereafter, if a landing is not completed, to a
position at which holding or en route obstacle clearance criteria apply. (See ICAO term
INSTRUMENT APPROACH OPERATIONS.)
A preplanned instrument flight rule (IFR) departure procedure published for pilot use, in graphic or textual
format, that provides obstruction clearance from the terminal area to the appropriate en route structure.
There are two types of DP, Obstacle Departure Procedure (ODP), printed either textually or graphically, and,
Standard Instrument Departure (SID), which is always printed graphically. (See IFR TAKEOFF MINIMUMS AND DEPARTURE
PROCEDURES.) (See OBSTACLE DEPARTURE PROCEDURE.) (See STANDARD INSTRUMENT DEPARTURE.) (Refer to
AIM.)
A runway equipped with electronic and visual navigation aids for which a precision or nonprecision approach
procedure having straight-in landing minimums has been approved.
[ICAO] One of the following types of runways intended for the operation of aircraft using instrument
approach procedures:
Nonprecision Approach Runway: An instrument runway served by visual aids and a nonvisual aid
providing at least directional guidance adequate for a straight-in approach.
Precision Approach Runway, Category I: An instrument runway served by ILS and visual aids
intended for operations down to 60 m (200 feet) decision height and down to an RVR of the order of 800
m.
Precision Approach Runway, Category II: An instrument runway served by ILS and visual aids
intended for operations down to 30 m (100 feet) decision height and down to an RVR of the order of 400
m.
Precision Approach Runway, Category III: An instrument runway served by ILS to and along the
surface of the runway and:
Intended for operations down to an RVR of the order of 200 m (no decision height being applicable)
using visual aids during the final phase of landing;
Intended for operations down to an RVR of the order of 50 m (no decision height being applicable)
using visual aids for taxiing;
Intended for operations without reliance on visual reference for landing or taxiing.
Note 1: See Annex 10 Volume I, Part I, Chapter 3, for related ILS specifications.
Note 2: Visual aids need not necessarily be matched to the scale of nonvisual aids provided. The
criterion for the selection of visual aids is the conditions in which operations are intended to
be conducted.
INTEGRATED DEPARTURE/ARRIVAL CAPABILITY (IDAC)
A Tower/TRACON departure scheduling capability within TBFM that allows departures to be scheduled into
either an arrival flow or an en route flow. IDAC provides a mechanism for electronic coordination of
departure release times.
INTEGRITY
The ability of a system to provide timely warnings to users when the system should not be used for
navigation.
[ICAO] That segment of an instrument approach procedure between either the intermediate approach fix and the
final approach fix or point, or between the end of a reversal, race track or dead reckoning track procedure
and the final approach fix or point, as appropriate.
INTERMEDIATE FIX
The fix that identifies the beginning of the intermediate approach segment of an instrument approach
procedure. The fix is not normally identified on the instrument approach chart as an intermediate fix (IF).
(See SEGMENTS OF AN INSTRUMENT APPROACH
PROCEDURE.)
INTERMEDIATE LANDING
On the rare occasion that this option is requested, it should be approved. The departure center, however,
must advise the ATCSCC so that the appropriate delay is carried over and assigned at the intermediate
airport. An intermediate landing airport within the arrival center will not be accepted without coordination
with and the approval of the ATCSCC.
INTERNATIONAL AIRPORT
Relating to international flight, it means:
An airport of entry which has been designated by the Secretary of Treasury or Commissioner of Customs as
an international airport for customs service.
A landing rights airport at which specific permission to land must be obtained from customs authorities
in advance of contemplated use.
Airports designated under the Convention on International Civil Aviation as an airport for use by
international commercial air transport and/or international general aviation.
[ICAO] Any airport designated by the Contracting State in whose territory it is situated as an airport of
entry and departure for international air traffic, where the formalities incident to customs, immigration,
public health, animal and plant quarantine and similar procedures are carried out.
INTERNATIONAL CIVIL AVIATION ORGANIZATION [ICAO]
A specialized agency of the United Nations whose objective is to develop the principles and techniques of
international air navigation and to foster planning and development of international civil air transport.
INTERNATIONAL NOTICE
A notice containing flight prohibitions, potential hostile situations, or other international/ foreign
oceanic airspace matters. These notices can be found on the International Notices website.
INTERROGATOR
The ground-based surveillance radar beacon transmitter-receiver, which normally scans in synchronism with a
primary radar, transmitting discrete radio signals which repetitiously request all transponders on the mode
being used to reply. The replies received are mixed with the primary radar returns and displayed on the same
plan position indicator (radar scope). Also, applied to the airborne element of the TACAN/DME system. (See TRANSPONDER.) (Refer to
AIM.)
INTERSECTING RUNWAYS
Two or more runways which cross or meet within their lengths. (See INTERSECTION.)
INTERSECTION
A point defined by any combination of courses, radials, or bearings of two or more navigational aids.
Used to describe the point where two runways, a runway and a taxiway, or two taxiways cross or meet.
INTERSECTION DEPARTURE
A departure from any runway intersection except the end of the runway. (See
INTERSECTION.)
A surface that is open for use but not per regulations.
ISR
Indicates the confidence level of the track requires 5NM separation. 3NM separation, 1 1/2NM separation, and
target resolution cannot be used.
J
JAMMING
Denotes emissions that do not mimic Global Navigation Satellite System (GNSS) signals (e.g., GPS and WAAS),
but rather interfere with the civil receiver's ability to acquire and track GNSS signals. Jamming can result
in denial of GNSS navigation, positioning, timing and aircraft dependent functions.
JET BLAST
Jet engine exhaust (thrust stream turbulence). (See WAKE TURBULENCE.)
JET ROUTE
A route designed to serve aircraft operations from 18,000 feet MSL up to and including flight level 450. The
routes are referred to as "J" routes with numbering to identify the designated route; e.g., J105. (See CLASS A AIRSPACE.) (Refer to 14 CFR Part 71.)
JET STREAM
A migrating stream of high-speed winds present at high altitudes.
JETTISONING OF EXTERNAL STORES
Airborne release of external stores; e.g., tiptanks, ordnance. (See FUEL DUMPING.)
(Refer to 14 CFR Part 91.)
An acronym for "Land and Hold Short Operation." These operations include landing and holding short of an
intersecting runway, a taxiway, a predetermined point, or an approach/departure flightpath.
LAHSO-DRY
Land and hold short operations on runways that are dry.
LAHSO-WET
Land and hold short operations on runways that are wet (but not contaminated).
LAND AND HOLD SHORT OPERATIONS
Operations which include simultaneous takeoffs and landings and/or simultaneous landings when a landing
aircraft is able and is instructed by the controller to hold-short of the intersecting runway/taxiway or
designated hold-short point. Pilots are expected to promptly inform the controller if the hold short
clearance cannot be accepted. (See PARALLEL RUNWAYS.) (Refer to
AIM.)
LAND-BASED AIR DEFENSE IDENTIFICATION ZONE (ADIZ)
An ADIZ over U.S. metropolitan areas, which is activated and deactivated as needed, with dimensions,
activation dates, and other relevant information disseminated via NOTAM. (See AIR DEFENSE IDENTIFICATION ZONE.)
LANDING AREA
Any locality either on land, water, or structures, including airports/heliports and intermediate landing
fields, which is used, or intended to be used, for the landing and takeoff of aircraft whether or not
facilities are provided for the shelter, servicing, or for receiving or discharging passengers or cargo.
[ICAO] That part of a movement area intended for the landing or take-off of aircraft.
LANDING DISTANCE AVAILABLE (LDA)
The runway length declared available and suitable for a landing airplane.
[ICAO] The length of runway which is declared available and suitable for the ground run of an aeroplane
landing.
LANDING DIRECTION INDICATOR
A device which visually indicates the direction in which landings and takeoffs should be made. (See TETRAHEDRON.) (Refer to
AIM.)
LANDING MINIMUMS
The minimum visibility prescribed for landing a civil aircraft while using an instrument approach procedure.
The minimum applies with other limitations set forth in
14 CFR Part 91 with respect to the Minimum
Descent Altitude (MDA) or Decision Height (DH) prescribed in the instrument approach procedures as follows:
Straight-in landing minimums: A statement of MDA and visibility, or DH and visibility, required
for a straight-in landing on a specified runway, or
Circling minimums: A statement of MDA and visibility required for the circle-to-land maneuver.
Note: Descent below the MDA or DH must meet the conditions stated in 14 CFR Section 91.175.
The last altitude/flight level assigned by ATC and acknowledged by the pilot. (See
MAINTAIN.) (Refer to 14 CFR Part 91.)
LATERAL NAVIGATION (LNAV)
A function of area navigation (RNAV) equipment which calculates, displays, and provides lateral guidance to
a profile or path.
LATERAL SEPARATION
The lateral spacing of aircraft at the same altitude by requiring operation on different routes or in
different geographical locations. (See SEPARATION.)
An airport where runway and obstruction lighting is available. (See AIRPORT
LIGHTING.) (Refer to
AIM.)
LIGHT GUN
A handheld directional light signaling device which emits a brilliant narrow beam of white, green, or red
light as selected by the tower controller. The color and type of light transmitted can be used to approve or
disapprove anticipated pilot actions where radio communication is not available. The light gun is used for
controlling traffic operating in the vicinity of the airport and on the airport movement area. (Refer to
AIM.)
LIGHT-SPORT AIRCRAFT (LSA)
An FAA-registered aircraft, other than a helicopter or powered-lift, that meets certain weight and
performance. Principally it is a single engine aircraft with a maximum of two seats and weighing no more
than 1,430 pounds if intended for operation on water, or 1,320 pounds if not. They must be of simple design
(fixed landing gear (except if intended for operations on water or a glider) piston powered,
non-pressurized, with a fixed or ground adjustable propeller), Performance is also limited to a maximum
airspeed in level flight of not more than 120 knots CAS, have a maximum never-exceed speed of not more than
120 knots CAS for a glider, and have a maximum stalling speed, without the use of lift-enhancing devices
(VS1 ) of not more than 45 knots CAS. They may be certificated as either Experimental LSA or as a Special
LSA aircraft. A minimum of a sport pilot certificate is required to operate light-sport aircraft." (Refer to
14 CFR Part 1, §1.1.)
LINE UP AND WAIT (LUAW)
Used by ATC to inform a pilot to taxi onto the departure runway to line up and wait. It is not authorization
for takeoff. It is used when takeoff clearance cannot immediately be issued because of traffic or other
reasons. (See CLEARED FOR TAKEOFF.)
LOCAL AIRPORT ADVISORY (LAA)
A service available only in Alaska and provided by facilities, which are located on the landing airport,
have a discrete ground-to-air communication frequency or the tower frequency when the tower is closed,
automated weather reporting with voice broadcasting, and a continuous ASOS/AWSS/AWOS data display, other
continuous direct reading instruments, or manual observations available to the specialist. (See AIRPORT ADVISORY AREA.)
LOCAL TRAFFIC
Aircraft operating in the traffic pattern or within sight of the tower, or aircraft known to be departing or
arriving from flight in local practice areas, or aircraft executing practice instrument approaches at the
airport. (See TRAFFIC PATTERN.)
The locus of points, in any given horizontal plane, at which the DDM (difference in depth of modulation) is
zero.
LOCALIZER OFFSET
An angular offset of the localizer aligned with 3° of the runway alignment.
LOCALIZER TYPE DIRECTIONAL AID
A localizer with an angular offset that exceeds 3° of the runway alignment used for nonprecision
instrument approaches with utility and accuracy comparable to a localizer but which are not part of a
complete ILS. (Refer to
AIM.)
LOCALIZER TYPE DIRECTIONAL AID (LDA) PRECISION RUNWAY MONITOR (PRM) APPROACH
An approach, which includes a glidslope, used in conjunction with an ILS PRM, RNAV PRM or GLS PRM approach
to an adjacent runway to conduct Simultaneous Offset Instrument Approaches (SOIA) to parallel runways whose
centerlines are separated by less than 3,000 feet and at least 750 feet. NTZ monitoring is required to
conduct these approaches. (See SIMULTANEOUS OFFSET
INSTRUMENT APPROACH (SOIA).) (Refer to
AIM.)
LOCALIZER USABLE DISTANCE
The maximum distance from the localizer transmitter at a specified altitude, as verified by flight
inspection, at which reliable course information is continuously received. (Refer to
AIM.)
LOCATOR [ICAO]
An LM/MF NDB used as an aid to final approach.
Note: A locator usually has an average radius of rated coverage of between 18.5 and 46.3 km (10 and 25
NM).
The longitudinal spacing of aircraft at the same altitude by a minimum distance expressed in units of time
or miles. (See SEPARATION.) (Refer to
AIM.)
LORAN
An electronic navigational system by which hyperbolic lines of position are determined by measuring the
difference in the time of reception of synchronized pulse signals from two fixed transmitters. Loran A
operates in the 1750-1950 kHz frequency band. Loran C and D operate in the 100-110 kHz frequency band. In
2010, the U.S. Coast Guard terminated all U.S. LORAN-C transmissions. (Refer to
AIM.)
LOST COMMUNICATIONS
Loss of the ability to communicate by radio. Aircraft are sometimes referred to as NORDO (No Radio).
Standard pilot procedures are specified in
14 CFR Part 91. Radar controllers issue
procedures for pilots to follow in the event of lost communications during a radar approach when weather
reports indicate that an aircraft will likely encounter IFR weather conditions during the approach. (Refer
to 14 CFR Part 91.) (Refer to
AIM.)
LOST LINK
An interruption or loss of the control link, or when the pilot is unable to effect control of the aircraft
and, as a result, the UA will perform a predictable or planned maneuver. Loss of command and control link
between the Control Station and the aircraft. There are two types of links:
An uplink which transmits command instructions to the aircraft, and
A downlink which transmits the status of the aircraft and provides situational awareness to the pilot.
LOST LINK PROCEDURE
Preprogrammed or predetermined mitigations to ensure the continued safe operation of the UA in the event of
a lost link (LL). In the event positive link cannot be established, flight termination must be implemented.
LOW ALTITUDE AIRWAY STRUCTURE
The network of airways serving aircraft operations up to but not including 18,000 feet MSL. (See
AIRWAY.) (Refer to
AIM.)
LOW ALTITUDE ALERT, CHECK YOUR ALTITUDE IMMEDIATELY
LOW ALTITUDE AUTHORIZATION AND NOTIFICATION CAPABILITY (LAANC)
FAA and industry collaboration which automates the process of obtaining a required authorization for
operations in controlled airspace.
LOW APPROACH
An approach over an airport or runway following an instrument approach or a VFR approach including the
go-around maneuver where the pilot intentionally does not make contact with the runway. (Refer to
AIM.)
LOW FREQUENCY
The frequency band between 30 and 300 kHz. (Refer to
AIM.)
LPV
A type of approach with vertical guidance (APV) based on WAAS, published on RNAV (GPS) approach charts. This
procedure takes advantage of the precise lateral guidance available from WAAS. The minima is published as a
decision altitude (DA).
The ratio of true airspeed to the speed of sound; e.g., MACH .82, MACH 1.6. (See
AIRSPEED.)
MACH TECHNIQUE [ICAO]
Describes a control technique used by air traffic control whereby turbojet aircraft operating successively
along suitable routes are cleared to maintain appropriate MACH numbers for a relevant portion of the en
route phase of flight. The principle objective is to achieve improved utilization of the airspace and to
ensure that separation between successive aircraft does not decrease below the established minima.
MAHWP
Missed Approach Holding Waypoint
MAINTAIN
Concerning altitude/flight level, the term means to remain at the altitude/flight level specified. The
phrase "climb and" or "descend and" normally precedes "maintain" and the altitude assignment; e.g.,
"descend and maintain 5,000."
Concerning other ATC instructions, the term is used in its literal sense; e.g., maintain VFR.
MAINTENANCE PLANNING FRICTION LEVEL
The friction level specified in AC 150/5320-12, Measurement, Construction, and Maintenance of Skid Resistant
Airport Pavement Surfaces, which represents the friction value below which the runway pavement surface
remains acceptable for any category or class of aircraft operations but which is beginning to show signs of
deterioration. This value will vary depending on the particular friction measurement equipment used.
MAKE SHORT APPROACH
Used by ATC to inform a pilot to alter his/her traffic pattern so as to make a short final approach. (See TRAFFIC PATTERN.)
MAN PORTABLE AIR DEFENSE SYSTEMS (MANPADS)
MANPADS are lightweight, shoulder launched, missile systems used to bring down aircraft and create mass
casualties. The potential for MANPADS use against airborne aircraft is real and requires familiarity with
the subject. Terrorists choose MANPADS because the weapons are low cost, highly mobile, require minimal
setup time, and are easy to use and maintain. Although the weapons have limited range, and their accuracy is
affected by poor visibility and adverse weather, they can be fired from anywhere on land or from boats where
there is unrestricted visibility to the target.
MANDATORY ALTITUDE
An altitude depicted on an instrument Approach Procedure Chart requiring the aircraft to maintain altitude
at the depicted value.
An electronic navigation facility transmitting a 75 MHz vertical fan or bone shaped radiation pattern.
Marker beacons are identified by their modulation frequency and keying code, and when received by compatible
airborne equipment, indicate to the pilot, both aurally and visually, that he/she is passing over the
facility. (See INNER MARKER.) (See MIDDLE MARKER.)
(See OUTER MARKER.) (Refer to
AIM.)
A published altitude representing the maximum usable altitude or flight level for an airspace structure or
route segment. It is the highest altitude on a Federal airway, jet route, area navigation low or high route,
or other direct route for which an MEA is designated in
14 CFR Part 95 at which adequate reception of
navigation aid signals is assured.
MAXIMUM GROSS OPERATING WEIGHT (MGOW)
The maximum gross weight of an aircraft, including fuel and any external objects, at any point during the
flight.
MAYDAY
The international radio telephony distress signal. When repeated three times, it indicates imminent and
grave danger and that immediate assistance is requested. (See PAN-PAN.) (Refer to
AIM.)
An unscheduled planning forecast describing conditions expected to begin within 4 to 12 hours which may
impact the flow of air traffic in a specific center's (ARTCC) area.
METER FIX ARC
A semicircle, equidistant from a meter fix, usually in low altitude relatively close to the meter fix, used
to help TBFM/ERAM calculate a meter time, and determine appropriate sector meter list assignments for
aircraft not on an established arrival route or assigned a meter fix.
METER REFERENCE ELEMENT (MRE)
A constraint point through which traffic flows are managed. An MRE can be the runway threshold, a meter fix,
or a meter arc.
METER REFERENCE POINT LIST (MRP)
A list of TBFM delay information conveyed to the controller on the situation display via the Meter Reference
Point View, commonly known as the "Meter List".
METERING
A method of time-regulating traffic flows in the en route and terminal environments.
METERING AIRPORTS
Airports adapted for metering and for which optimum flight paths are defined. A maximum of 15 airports may
be adapted.
METERING FIX
A fix along an established route from over which aircraft will be metered prior to entering terminal
airspace. Normally, this fix should be established at a distance from the airport which will facilitate a
profile descent 10,000 feet above airport elevation (AAE) or above.
A small downburst with outbursts of damaging winds extending 2.5 miles or less. In spite of its small
horizontal scale, an intense microburst could induce wind speeds as high as 150 knots (Refer to
AIM.)
MICRO-EN ROUTE AUTOMATED RADAR TRACKING SYSTEM (MEARTS)
An automated radar and radar beacon tracking system capable of employing both short-range (ASR) and
long-range (ARSR) radars. This microcomputer driven system provides improved tracking, continuous data
recording, and use of full digital radar displays.
A marker beacon that defines a point along the glideslope of an ILS normally located at or near the point of
decision height (ILS Category I). It is keyed to transmit alternate dots and dashes, with the alternate dots
and dashes keyed at the rate of 95 dot/dash combinations per minute on a 1300 Hz tone, which is received
aurally and visually by compatible airborne equipment. (See INSTRUMENT
LANDING SYSTEM.) (See MARKER BEACON.) (Refer to
AIM.)
MILES-IN-TRAIL
A specified distance between aircraft, normally, in the same stratum associated with the same destination or
route of flight.
MILITARY AUTHORITY ASSUMES RESPONSIBILITY FOR SEPARATION OF AIRCRAFT
A condition whereby the military services involved assume responsibility for separation between
participating military aircraft in the ATC system. It is used only for required IFR operations which are
specified in letters of agreement or other appropriate FAA or military documents.
MILITARY LANDING ZONE
A landing strip used exclusively by the military for training. A military landing zone does not carry a
runway designation.
The lowest altitude at certain fixes at which an aircraft must cross when proceeding in the direction of a
higher minimum en route IFR altitude (MEA). (See MINIMUM EN ROUTE IFR
ALTITUDE.)
MINIMUM DESCENT ALTITUDE
The lowest altitude, expressed in feet above mean sea level, to which descent is authorized on final
approach or during circle-to-land maneuvering in execution of a standard instrument approach procedure where
no electronic glideslope is provided. (See NONPRECISION APPROACH
PROCEDURE.)
MINIMUM EN ROUTE IFR ALTITUDE (MEA)
The lowest published altitude between radio fixes which assures acceptable navigational signal coverage and
meets obstacle clearance requirements between those fixes. The MEA prescribed for a Federal airway or
segment thereof, area navigation low or high route, or other direct route applies to the entire width of the
airway, segment, or route between the radio fixes defining the airway, segment, or route. (Refer to
14 CFR Part 91.) (Refer to
14 CFR Part 95.) (Refer to
AIM.)
MINIMUM FRICTION LEVEL
The friction level specified in AC 150/5320-12, Measurement, Construction, and Maintenance of Skid Resistant
Airport Pavement Surfaces, that represents the minimum recommended wet pavement surface friction value for
any turbojet aircraft engaged in LAHSO. This value will vary with the particular friction measurement
equipment used.
MINIMUM FUEL
Indicates that an aircraft's fuel supply has reached a state where, upon reaching the destination, it can
accept little or no delay. This is not an emergency situation but merely indicates an emergency situation is
possible should any undue delay occur. (Refer to
AIM.)
MINIMUM HOLDING ALTITUDE
The lowest altitude prescribed for a holding pattern which assures navigational signal coverage,
communications, and meets obstacle clearance requirements.
MINIMUM IFR ALTITUDES (MIA)
Minimum altitudes for IFR operations as prescribed in
14 CFR Part 91. These altitudes are published
on aeronautical charts and prescribed in
14 CFR Part 95 for airways and routes, and in
14 CFR Part 97 for standard instrument
approach procedures. If no applicable minimum altitude is prescribed in
14 CFR Part 95 or
14 CFR Part 97, the following minimum IFR
altitude applies:
In designated mountainous areas, 2,000 feet above the highest obstacle within a horizontal distance of 4
nautical miles from the course to be flown; or
Other than mountainous areas, 1,000 feet above the highest obstacle within a horizontal distance of 4
nautical miles from the course to be flown; or
As otherwise authorized by the Administrator or assigned by ATC.
The lowest published altitude in effect between radio fixes on VOR airways, off-airway routes, or route
segments which meets obstacle clearance requirements for the entire route segment and which assures
acceptable navigational signal coverage only within 25 statute (22 nautical) miles of a VOR. (Refer to
14 CFR Part 91.) (Refer to
14 CFR Part 95.)
MINIMUM RECEPTION ALTITUDE
The lowest altitude at which an intersection can be determined. (Refer to
14 CFR Part 95.)
MINIMUM SAFE ALTITUDE (MSA)
The Minimum Safe Altitude (MSA) specified in
14 CFR Part 91 for various aircraft
operations.
Altitudes depicted on approach charts or departure procedure (DP) graphic charts which provide at least
1,000 feet of obstacle clearance for emergency use. These altitudes will be identified as Minimum Safe
Altitudes or Emergency Safe Altitudes and are established as follows:
Minimum Safe Altitude (MSA). Altitudes depicted on approach charts or on a DP graphic chart which
provide at least 1,000 feet of obstacle clearance within a 25-mile radius of the navigation facility,
waypoint, or airport reference point upon which the MSA is predicated. MSAs are for emergency use only
and do not necessarily assure acceptable navigational signal coverage. (See ICAO term Minimum Sector
Altitude.)
Emergency Safe Altitude (ESA). Altitudes depicted on approach charts which provide at least 1,000
feet of obstacle clearance in nonmountainous areas and 2,000 feet of obstacle clearance in
designated mountainous areas within a 100-mile radius of the navigation facility or waypoint used as
the ESA center. These altitudes are normally used only in military procedures and are identified on
published procedures as "Emergency Safe Altitudes."
MINIMUM SAFE ALTITUDE WARNING (MSAW)
A function of the EAS and STARS computer that aids the controller by alerting him/her when a tracked Mode C
equipped aircraft is below or is predicted by the computer to go below a predetermined minimum safe
altitude. (Refer to
AIM.)
MINIMUM SECTOR ALTITUDE [ICAO]
The lowest altitude which may be used under emergency conditions which will provide a minimum clearance of
300 m (1,000 feet) above all obstacles located in an area contained within a sector of a circle of 46 km (25
NM) radius centered on a radio aid to navigation.
The lowest MSL altitude at which an IFR aircraft will be vectored by a radar controller, except as otherwise
authorized for radar approaches, departures, and missed approaches. The altitude meets IFR obstacle
clearance criteria. It may be lower than the published MEA along an airway or J-route segment. It may be
utilized for radar vectoring only upon the controller's determination that an adequate radar return is being
received from the aircraft being controlled. Charts depicting minimum vectoring altitudes are normally
available only to the controllers and not to pilots. (Refer to
AIM.)
MINUTES-IN-TRAIL
A specified interval between aircraft expressed in time. This method would more likely be utilized
regardless of altitude.
A maneuver conducted by a pilot when an instrument approach cannot be completed to a landing. The route
of flight and altitude are shown on instrument approach procedure charts. A pilot executing a missed
approach prior to the Missed Approach Point (MAP) must continue along the final approach to the MAP.
A term used by the pilot to inform ATC that he/she is executing the missed approach.
At locations where ATC radar service is provided, the pilot should conform to radar vectors when
provided by ATC in lieu of the published missed approach procedure.
The letter or number assigned to a specific pulse spacing of radio signals transmitted or received by ground
interrogator or airborne transponder components of the Air Traffic Control Radar Beacon System (ATCRBS).
Mode A (military Mode 3) and Mode C (altitude reporting) are used in air traffic control. (See INTERROGATOR.) (See RADAR.) (See TRANSPONDER.) (See ICAO term
MODE.) (Refer to
AIM.)
MODE (SSR MODE) [ICAO]
The letter or number assigned to a specific pulse spacing of the interrogation signals transmitted by an
interrogator. There are 4 modes, A, B, C and D specified in Annex 10, corresponding to four different
interrogation pulse spacings.
MODE C INTRUDER ALERT
A function of certain air traffic control automated systems designed to alert radar controllers to existing
or pending situations between a tracked target (known IFR or VFR aircraft) and an untracked target (unknown
IFR or VFR aircraft) that requires immediate attention/action. (See CONFLICT
ALERT.)
MODEL AIRCRAFT
An unmanned aircraft that is: (1) capable of sustained flight in the atmosphere; (2) flown within visual
line of sight of the person operating the aircraft; and (3) flown for hobby or recreational purposes.
MONITOR
(When used with communication transfer) listen on a specific frequency and stand by for instructions. Under
normal circumstances do not establish communications.
MONITOR ALERT (MA)
A function of the TFMS that provides traffic management personnel with a tool for predicting potential
capacity problems in individual operational sectors. The MA is an indication that traffic management
personnel need to analyze a particular sector for actual activity and to determine the required action(s),
if any, needed to control the demand.
MONITOR ALERT PARAMETER (MAP)
The number designated for use in monitor alert processing by the TFMS. The MAP is designated for each
operational sector for increments of 15 minutes.
MOSAIC/MULTI-SENSOR MODE
Accepts positional data from multiple approved surveillance sources. Targets are displayed from a single
source according to the hierarchy of the sources assigned in a given geographic area.
MOUNTAIN WAVE
Mountain waves occur when air is being blown over a mountain range or even the ridge of a sharp bluff area.
As the air hits the upwind side of the range, it starts to climb, thus creating what is generally a smooth
updraft which turns into a turbulent downdraft as the air passes the crest of the ridge. Mountain Waves can
cause significant fluctuations in airspeed and altitude with or without associated turbulence. (Refer to
AIM.)
MOVEMENT AREA
The runways, taxiways, and other areas of an airport/heliport which are utilized for taxiing/hover taxiing,
air taxiing, takeoff, and landing of aircraft, exclusive of loading ramps and parking areas. At those
airports/heliports with a tower, specific approval for entry onto the movement area must be obtained from
ATC.
[ICAO] That part of an aerodrome to be used for the takeoff, landing and taxiing of aircraft, consisting of
the maneuvering area and the apron(s).
MOVING AIRSPACE RESERVATION
The term used in oceanic ATC for airspace that encompasses oceanic activities and advances with the mission
progress; i.e., the reservation moves with the aircraft or flight.
(See MOVING ALTITUDE RESERVATION.)
MOVING ALTITUDE RESERVATION
An altitude reservation which encompasses en route activities and advances with the mission progress; i.e.,
the reservation moves with the aircraft or flight.
MOVING TARGET INDICATOR
An electronic device which will permit radar scope presentation only from targets which are in motion. A
partial remedy for ground clutter.
A mobile service not open to public correspondence used to provide communications essential to conduct the
activities being performed by or directed from private aircraft.
MULTIPLE RUNWAYS
The utilization of a dedicated arrival runway(s) for departures and a dedicated departure runway(s) for
arrivals when feasible to reduce delays and enhance capacity.
The common network of U.S. airspace; air navigation facilities, equipment and services, airports or landing
areas; aeronautical charts, information and services; rules, regulations and procedures, technical
information, and manpower and material. Included are system components shared jointly with the military.
NATIONAL BEACON CODE ALLOCATION PLAN AIRSPACE
Airspace over United States territory located within the North American continent between Canada and Mexico,
including adjacent territorial waters outward to about boundaries of oceanic control areas (CTA)/Flight
Information Regions (FIR). (See FLIGHT INFORMATION REGION.)
NATIONAL FLIGHT DATA DIGEST (NFDD)
A daily (except weekends and Federal holidays) publication of flight information appropriate to aeronautical
charts, aeronautical publications, Notices to Air Missions, or other media serving the purpose of providing
operational flight data essential to safe and efficient aircraft operations.
NATIONAL SEARCH AND RESCUE PLAN
An inter-agency agreement which provides for the effective utilization of all available facilities in all
types of search and rescue missions.
VOR, VORTAC, and TACAN aids are classed according to their operational use. The three classes of NAVAIDs
are:
T - Terminal.
L - Low altitude.
H - High altitude.
Note: The normal service range for T, L, and H class aids is found in the AIM. Certain operational
requirements make it necessary to use some of these aids at greater service ranges than specified.
Extended range is made possible through flight inspection determinations. Some aids also have lesser
service range due to location, terrain, frequency protection, etc. Restrictions to service range are
listed in Chart Supplement U.S.
NAVIGABLE AIRSPACE
Airspace at and above the minimum flight altitudes prescribed in the CFRs including airspace needed for safe
takeoff and landing. (Refer to
14 CFR Part 91.)
NAVIGATION REFERENCE SYSTEM (NRS)
The NRS is a system of waypoints developed for use within the United States for flight planning and
navigation without reference to ground based navigational aids. The NRS waypoints are located in a grid
pattern along defined latitude and longitude lines. The initial use of the NRS will be in the high altitude
environment. The NRS waypoints are intended for use by aircraft capable of point-to-point navigation.
NAVIGATION SPECIFICATION [ICAO]
A set of aircraft and flight crew requirements needed to support performance based navigation operations
within a defined airspace. There are two kinds of navigation specifications:
RNP specification. A navigation specification based on area navigation that includes the requirement for
performance monitoring and alerting, designated by the prefix RNP; e.g., RNP 4, RNP APCH.
RNAV specification. A navigation specification based on area navigation that does not include the
requirement for performance monitoring and alerting, designated by the prefix RNAV; e.g., RNAV 5, RNAV
1.
Note: The Performance based Navigation Manual (Doc 9613), Volume II contains detailed guidance on
navigation specifications.
NAVIGATIONAL AID
Any visual or electronic device airborne or on the surface which provides point-to-point guidance
information or position data to aircraft in flight. (See AIR NAVIGATION
FACILITY.)
The time between the end of evening civil twilight and the beginning of morning civil twilight, as published
in the Air Almanac, converted to local time.
[ICAO] The hours between the end of evening civil twilight and the beginning of morning civil twilight or
such other period between sunset and sunrise as may be specified by the appropriate authority.
Note: Civil twilight ends in the evening when the center of the sun's disk is 6 degrees below the horizon
and begins in the morning when the center of the sun's disk is 6 degrees below the horizon.
NO GYRO APPROACH
A radar approach/vector provided in case of a malfunctioning gyro-compass or directional gyro. Instead of
providing the pilot with headings to be flown, the controller observes the radar track and issues control
instructions "turn right/left" or "stop turn" as appropriate. (Refer to
AIM.)
The NTZ is a 2,000 foot wide zone, located equidistant between parallel runway or SOIA final approach
courses in which flight is normally not allowed.
NONAPPROACH CONTROL TOWER
Authorizes aircraft to land or takeoff at the airport controlled by the tower or to transit the Class D
airspace. The primary function of a nonapproach control tower is the sequencing of aircraft in the traffic
pattern and on the landing area. Nonapproach control towers also separate aircraft operating under
instrument flight rules clearances from approach controls and centers. They provide ground control services
to aircraft, vehicles, personnel, and equipment on the airport movement area.
NONCOMMON ROUTE/PORTION
That segment of a North American Route between the inland navigation facility and a designated North
American terminal.
NON-COOPERATIVE SURVEILLANCE
Any surveillance system, such as primary radar, that is not dependent upon the presence of any equipment on
the aircraft or vehicle to be tracked. (See COOPERATIVE SURVEILLANCE.)
(See RADAR.)
NONDIRECTIONAL BEACON
An L/MF or UHF radio beacon transmitting nondirectional signals whereby the pilot of an aircraft equipped
with direction finding equipment can determine his/her bearing to or from the radio beacon and "home" on or
track to or from the station. When the radio beacon is installed in conjunction with the Instrument Landing
System marker, it is normally called a Compass Locator. (See AUTOMATIC
DIRECTION FINDER.) (See COMPASS LOCATOR.)
NONMOVEMENT AREAS
Taxiways and apron (ramp) areas not under the control of air traffic.
A standard instrument approach procedure in which no electronic glideslope is provided; e.g., VOR, TACAN,
NDB, LOC, ASR, LDA, or SDF approaches.
NONRADAR
Precedes other terms and generally means without the use of radar, such as:
Nonradar Approach. Used to describe instrument approaches for which course guidance on final approach is
not provided by ground-based precision or surveillance radar. Radar vectors to the final approach course
may or may not be provided by ATC. Examples of nonradar approaches are VOR, NDB, TACAN, ILS, RNAV, and
GLS approaches. (See FINAL APPROACH COURSE.) (See FINAL APPROACH-IFR.) (See INSTRUMENT APPROACH PROCEDURE.) (See
RADAR APPROACH.)
Nonradar Arrival. An aircraft arriving at an airport without radar service or at an airport served by a
radar facility and radar contact has not been established or has been terminated due to a lack of radar
service to the airport. (See RADAR ARRIVAL.) (See
RADAR SERVICE.)
Nonradar Route. A flight path or route over which the pilot is performing his/her own navigation. The
pilot may be receiving radar separation, radar monitoring, or other ATC services while on a nonradar
route. (See RADAR ROUTE.)
Nonradar Separation. The spacing of aircraft in accordance with established minima without the use of
radar; e.g., vertical, lateral, or longitudinal separation. (See RADAR
SEPARATION.
NONRESTRICTIVE ROUTING (NRR)
Portions of a proposed route of flight where a user can flight plan the most advantageous flight path with
no requirement to make reference to ground based NAVAIDs.
Aircraft that cannot or do not communicate by radio when radio communication is required are referred to as
"NORDO." (See LOST COMMUNICATIONS.)
NORMAL OPERATING ZONE (NOZ)
The NOZ is the operating zone within which aircraft flight remains during normal independent simultaneous
parallel ILS approaches.
NORTH AMERICAN ROUTE
A numerically coded route preplanned over existing airway and route systems to and from specific coastal
fixes serving the North Atlantic. North American Routes consist of the following:
Common Route/Portion. That segment of a North American Route between the inland navigation facility and
the coastal fix.
Noncommon Route/Portion. That segment of a North American Route between the inland navigation facility
and a designated North American terminal.
Inland Navigation Facility. A navigation aid on a North American Route at which the common route and/or
the noncommon route begins or ends.
Coastal Fix. A navigation aid or intersection where an aircraft transitions between the domestic route
structure and the oceanic route structure.
NORTH AMERICAN ROUTE PROGRAM (NRP)
The NRP is a set of rules and procedures which are designed to increase the flexibility of user flight
planning within published guidelines.
NORTH ATLANTIC HIGH LEVEL AIRSPACE (NAT HLA)
That volume of airspace (as defined in ICAO Document 7030) between FL 285 and FL 420 within the Oceanic
Control Areas of Bodo Oceanic, Gander Oceanic, New York Oceanic East, Reykjavik, Santa Maria, and Shanwick,
excluding the Shannon and Brest Ocean Transition Areas. ICAO Doc 007 North Atlantic Operations and Airspace
Manual provides detailed information on related aircraft and operational requirements.
NORTH PACIFIC
An organized route system between the Alaskan west coast and Japan.
NOT STANDARD
Varying from what is expected or published. For use in NOTAMs only.
[ICAO] A notice containing information concerning the establishment, condition or change in any aeronautical
facility, service, procedure or hazard, the timely knowledge of which is essential to personnel concerned
with flight operations.
I Distribution: Distribution by means of telecommunication.
II Distribution: Distribution by means other than telecommunications.
NOTICE TO AIR MISSIONS (NOTAM)
A notice containing information (not known sufficiently in advance to publicize by other means) concerning
the establishment, condition, or change in any component (facility, service, or procedure of, or hazard in
the National Airspace System) the timely knowledge of which is essential to personnel concerned with flight
operations.
NOTAM(D): A NOTAM given (in addition to local dissemination) distant dissemination beyond the
area of responsibility of the Flight Service Station. These NOTAMs will be stored and available until
canceled.
FDC NOTAM: A NOTAM regulatory in nature, transmitted by USNOF and given system wide
dissemination.
A traffic advisory issued by ATC to advise pilots that targets on the radar scope are too numerous to issue
individually. (See TRAFFIC ADVISORIES.)
O
OBSTACLE
An existing object, object of natural growth, or terrain at a fixed geographical location or which may be
expected at a fixed location within a prescribed area with reference to which vertical clearance is or must
be provided during flight operation.
OBSTACLE DEPARTURE PROCEDURE (ODP)
A preplanned instrument flight rule (IFR) departure procedure printed for pilot use in textual or graphic
form to provide obstruction clearance via the least onerous route from the terminal area to the appropriate
en route structure. ODPs are recommended for obstruction clearance and may be flown without ATC clearance
unless an alternate departure procedure (SID or radar vector) has been specifically assigned by ATC. (See IFR TAKEOFF MINIMUMS AND DEPARTURE
PROCEDURES.) (See STANDARD INSTRUMENT DEPARTURE.) (Refer to
AIM.)
OBSTACLE FREE ZONE
The OFZ is a three dimensional volume of airspace which protects for the transition of aircraft to and from
the runway. The OFZ clearing standard precludes taxiing and parked airplanes and object penetrations, except
for frangible NAVAID locations that are fixed by function. Additionally, vehicles, equipment, and personnel
may be authorized by air traffic control to enter the area using the provisions of FAA Order JO 7110.65,
paragraph 3-1-5, Vehicles/Equipment/Personnel Near/On Runways. The runway OFZ and when applicable, the
inner-approach OFZ, and the inner-transitional OFZ, comprise the OFZ.
Runway OFZ. The runway OFZ is a defined volume of airspace centered above the runway. The runway OFZ is
the airspace above a surface whose elevation at any point is the same as the elevation of the nearest
point on the runway centerline. The runway OFZ extends 200 feet beyond each end of the runway. The width
is as follows:
For runways serving large airplanes, the greater of:
(a) 400 feet, or
(b) 180 feet, plus the wingspan of the most demanding airplane, plus 20 feet per 1,000 feet of
airport elevation.
For runways serving only small airplanes:
(a) 300 feet for precision instrument runways.
(b) 250 feet for other runways serving small airplanes with approach speeds of 50 knots, or
more.
(c) 120 feet for other runways serving small airplanes with approach speeds of less than 50
knots.
Inner-approach OFZ. The inner-approach OFZ is a defined volume of airspace centered on the approach
area. The inner-approach OFZ applies only to runways with an approach lighting system. The
inner-approach OFZ begins 200 feet from the runway threshold at the same elevation as the runway
threshold and extends 200 feet beyond the last light unit in the approach lighting system. The width of
the inner-approach OFZ is the same as the runway OFZ and rises at a slope of 50 (horizontal) to 1
(vertical) from the beginning.
Inner-transitional OFZ. The inner transitional surface OFZ is a defined volume of airspace along the
sides of the runway and inner-approach OFZ and applies only to precision instrument runways. The
inner-transitional surface OFZ slopes 3 (horizontal) to 1 (vertical) out from the edges of the runway
OFZ and inner-approach OFZ to a height of 150 feet above the established airport elevation.
A light or one of a group of lights, usually red or white, frequently mounted on a surface structure or
natural terrain to warn pilots of the presence of an obstruction.
OCEANIC AIRSPACE
Airspace over the oceans of the world, considered international airspace, where oceanic separation and
procedures per the International Civil Aviation Organization are applied. Responsibility for the provisions
of air traffic control service in this airspace is delegated to various countries, based generally upon
geographic proximity and the availability of the required resources.
OCEANIC ERROR REPORT
A report filed when ATC observes an Oceanic Error as defined by FAA Order JO 7210.632, Air Traffic
Organization Occurrence Reporting.
OCEANIC PUBLISHED ROUTE
A route established in international airspace and charted or described in flight information publications,
such as Route Charts, DOD Enroute Charts, Chart Supplements, NOTAMs, and Track Messages.
OCEANIC TRANSITION ROUTE
An ATS route established for the purpose of transitioning aircraft to/from an organized track system.
A term used to describe a situation where an aircraft has reported a position fix or is observed on radar at
a point not on the ATC-approved route of flight.
OFF-ROUTE OBSTRUCTION CLEARANCE ALTITUDE (OROCA)
A published altitude which provides terrain and obstruction clearance with a 1,000 foot buffer in
non-mountainous areas and a 2,000 foot buffer in designated mountainous areas within the United States, and
a 3,000 foot buffer outside the US ADIZ. These altitudes are not assessed for NAVAID signal coverage, air
traffic control surveillance, or communications coverage, and are published for general situational
awareness, flight planning, and in-flight contingency use.
OFF-ROUTE VECTOR
A vector by ATC which takes an aircraft off a previously assigned route. Altitudes assigned by ATC during
such vectors provide required obstacle clearance.
OFFSET PARALLEL RUNWAYS
Staggered runways having centerlines which are parallel.
OFFSHORE/CONTROL AIRSPACE AREA
That portion of airspace between the U.S. 12 NM limit and the oceanic CTA/FIR boundary within which air
traffic control is exercised. These areas are established to provide air traffic control services.
Offshore/Control Airspace Areas may be classified as either Class A airspace or Class E airspace.
Used to indicate that an aircraft is established on the route centerline.
Used by ATC to advise a pilot making a radar approach that his/her aircraft is lined up on the final
approach course. (See ON-COURSE INDICATION.)
ON-COURSE INDICATION
An indication on an instrument, which provides the pilot a visual means of determining that the aircraft is
located on the centerline of a given navigational track, or an indication on a radar scope that an aircraft
is on a given track.
ONE-MINUTE WEATHER
The most recent one minute updated weather broadcast received by a pilot from an uncontrolled airport
ASOS/AWSS/AWOS.
Operations of small unmanned aircraft over people. (Refer to 14 CFR Part 107)
OPERATIONS SPECIFICATIONS [ICAO]
The authorizations, conditions and limitations associated with the air operator certificate and subject to
the conditions in the operations manual.
OPERATOR (UAS)
The owner and/or remote pilot of a UAS.
OPPOSITE DIRECTION AIRCRAFT
Aircraft are operating in opposite directions when:
They are following the same track in reciprocal directions; or
Their tracks are parallel and the aircraft are flying in reciprocal directions; or
Their tracks intersect at an angle of more than 135°.
OPTION APPROACH
An approach requested and conducted by a pilot which will result in either a touch-and-go, missed approach,
low approach, stop-and-go, or full stop landing. Pilots should advise ATC if they decide to remain on the
runway, of any delay in their stop and go, delay clearing the runway, or are unable to comply with the
instruction(s). (See CLEARED FOR THE OPTION.) (Refer to
AIM.)
ORGANIZED TRACK SYSTEM
A series of ATS routes which are fixed and charted; i.e., CEP, NOPAC, or flexible and described by NOTAM;
i.e., NAT TRACK MESSAGE.
The conversation is ended and no response is expected.
OUT OF SERVICE/UNSERVICEABLE (U/S)
When a piece of equipment, a NAVAID, a facility or a service is not operational, certified (if required) and
immediately "available" for Air Traffic or public use.
OUTER AREA (associated with Class C airspace)
Nonregulatory airspace surrounding designated Class C airspace airports wherein ATC provides radar vectoring
and sequencing on a full-time basis for all IFR and participating VFR aircraft. The service provided in the
outer area is called Class C service which includes: IFR/IFR separation; IFR/VFR traffic advisories and
conflict resolution; and VFR/VFR traffic advisories and, as appropriate, safety alerts. The normal radius
will be 20 nautical miles with some variations based on site-specific requirements. The outer area extends
outward from the primary Class C airspace airport and extends from the lower limits of radar/radio coverage
up to the ceiling of the approach control's delegated airspace excluding the Class C charted area and other
airspace as appropriate. (See CONFLICT RESOLUTION.) (See CONTROLLED AIRSPACE.)
A general term used within ATC to describe fixes in the terminal area, other than the final approach fix.
Aircraft are normally cleared to these fixes by an Air Route Traffic Control Center or an Approach Control
Facility. Aircraft are normally cleared from these fixes to the final approach fix or final approach course.
OR An adapted fix along the converted route of flight, prior to the meter fix, for which crossing times are
calculated and displayed in the metering position list.
OUTER FIX ARC
A semicircle, usually about a 5070 mile radius from a meter fix, usually in high altitude, which is used by
CTAS/HOST to calculate outer fix times and determine appropriate sector meter list assignments for aircraft
on an established arrival route that will traverse the arc.
OUTER FIX TIME
A calculated time to depart the outer fix in order to cross the vertex at the ACLT. The time reflects
descent speed adjustments and any applicable delay time that must be absorbed prior to crossing the meter
fix.
OUTER MARKER
A marker beacon at or near the glideslope intercept altitude of an ILS approach. It is keyed to transmit two
dashes per second on a 400 Hz tone, which is received aurally and visually by compatible airborne equipment.
The OM is normally located four to seven miles from the runway threshold on the extended centerline of the
runway. (See INSTRUMENT LANDING SYSTEM.) (See MARKER BEACON.) (Refer to
AIM.)
OVER
My transmission is ended; I expect a response.
OVERHEAD MANEUVER
A series of predetermined maneuvers prescribed for aircraft (often in formation) for entry into the visual
flight rules (VFR) traffic pattern and to proceed to a landing. An overhead maneuver is not an instrument
flight rules (IFR) approach procedure. An aircraft executing an overhead maneuver is considered VFR and the
IFR flight plan is canceled when the aircraft reaches the "initial point" on the initial approach portion of
the maneuver. The pattern usually specifies the following:
The radio contact required of the pilot.
The speed to be maintained.
An initial approach 3 to 5 miles in length.
An elliptical pattern consisting of two 180 degree turns.
A break point at which the first 180 degree turn is started.
The direction of turns.
Altitude (at least 500 feet above the conventional pattern).
A "Roll-out" on final approach not less than 1/4 mile from the landing threshold and not less than 300
feet above the ground.
OVERLYING CENTER
The ARTCC facility that is responsible for arrival/departure operations at a specific terminal.
The international radio-telephony urgency signal. When repeated three times, indicates uncertainty or alert
followed by the nature of the urgency. (See MAYDAY.) (Refer to
AIM.)
Approaches to parallel runways by IFR aircraft which, when established inbound toward the airport on the
adjacent final approach courses, are radar-separated by at least 2 miles. (See FINAL APPROACH COURSE.) (See SIMULTANEOUS ILS APPROACHES.)
PARALLEL OFFSET ROUTE
A parallel track to the left or right of the designated or established airway/route. Normally associated
with Area Navigation (RNAV) operations. (See AREA NAVIGATION.)
PARALLEL RUNWAYS
Two or more runways at the same airport whose centerlines are parallel. In addition to runway number,
parallel runways are designated as L (left) and R (right) or, if three parallel runways exist, L (left), C
(center), and R (right).
Area navigation based on performance requirements for aircraft operating along an ATS route, on an
instrument approach procedure or in a designated airspace. Note: Performance requirements are expressed in
navigation specifications (RNAV specification, RNP specification) in terms of accuracy, integrity,
continuity, availability, and functionality needed for the proposed operation in the context of a particular
airspace concept.
PERMANENT ECHO
Radar signals reflected from fixed objects on the earth's surface; e.g., buildings, towers, terrain.
Permanent echoes are distinguished from "ground clutter" by being definable locations rather than large
areas. Under certain conditions they may be used to check radar alignment.
Military activity that requires locating individual photo targets and navigating to the targets at a
preplanned angle and altitude. The activity normally requires a lateral route width of 16 NM and altitude
range of 1,500 feet to 10,000 feet AGL.
PILOT BRIEFING
A service provided by the FSS to assist pilots in flight planning. Briefing items may include weather
information, NOTAMS, military activities, flow control information, and other items as requested. (Refer to
AIM.)
PILOT IN COMMAND
The pilot responsible for the operation and safety of an aircraft during flight time. (Refer to
14 CFR Part 91.)
PILOT WEATHER REPORT
A report of meteorological phenomena encountered by aircraft in flight. (Refer to
AIM.)
PILOT'S DISCRETION
When used in conjunction with altitude assignments, means that ATC has offered the pilot the option of
starting climb or descent whenever he/she wishes and conducting the climb or descent at any rate he/she
wishes. He/she may temporarily level off at any intermediate altitude. However, once he/she has vacated an
altitude, he/she may not return to that altitude.
A fix/waypoint that serves as a transition point from a departure procedure or the low altitude ground based
navigation structure into the high altitude waypoint system.
PLAN, EXECUTE, REVIEW, TRAIN, IMPROVE (PERTI)
A process that delivers a one-day detailed plan for NAS operations, and a two-day outlook, which sets NAS
performance goals for high impact constraints. PLAN: Increase lead time for identifying aviation system
constraint planning and goals while utilizing historical NAS performance data and constraints to derive
successful and/or improved advance planning strategies. EXECUTE: Set goals and a strategy. The Air Traffic
Control System Command Center (ATCSCC), FAA field facilities, and aviation stakeholders execute the strategy
and work to achieve the desired/planned outcomes. REVIEW: Utilize post event analysis and lessons learned to
define and implement future strategies and operational triggers based on past performance and outcomes, both
positive and negative. TRAIN: Develop training that includes rapid and continuous feedback to operational
personnel and provides increased data and weather knowledge and tools for analytical usage and planning.
IMPROVE: Implement better information sharing processes, technologies, and procedures that improve the
skills and technology needed to implement operational insights and improvements.
PLANS DISPLAY
A display available in EDST that provides detailed flight plan and predicted conflict information in textual
format for requested Current Plans and all Trial Plans. (See EN
ROUTE DECISION SUPPORT TOOL)
PLANVIEW GRAPHICAL USER INTERFACE (PGUI)
A TBFM display that provides a spatial display of individual aircraft track information.
A level of NRR service for aircraft that is based on traditional waypoints in their FMSs or RNAV equipage.
POLAR TRACK STRUCTURE
A system of organized routes between Iceland and Alaska which overlie Canadian MNPS Airspace.
POSITION REPORT
A report over a known location as transmitted by an aircraft to ATC. (Refer to
AIM.)
POSITION SYMBOL
A computer-generated indication shown on a radar display to indicate the mode of tracking.
POSITIVE CONTROL
The separation of all air traffic within designated airspace by air traffic control.
PRACTICE INSTRUMENT APPROACH
An instrument approach procedure conducted by a VFR or an IFR aircraft for the purpose of pilot training or
proficiency demonstrations.
PRE-DEPARTURE CLEARANCE
An application with the Terminal Data Link System (TDLS) that provides clearance information to subscribers,
through a service provider, in text to the cockpit or gate printer.
PRE-DEPARTURE REROUTE (PDRR)
A capability within the Traffic Flow Management System that enables ATC to quickly amend and execute revised
departure clearances that mitigate en route constraints or balance en route traffic flows.
PREARRANGED COORDINATION
A standardized procedure which permits an air traffic controller to enter the airspace assigned to another
air traffic controller without verbal coordination. The procedures are defined in a facility directive which
ensures approved separation between aircraft.
PREARRANGED COORDINATION PROCEDURES
A facility's standardized procedure that describes the process by which one controller shall allow an
aircraft to penetrate or transit another controller's airspace in a manner that assures approved separation
without individual coordination for each aircraft.
PRECIPITATION
Any or all forms of water particles (rain, sleet, hail, or snow) that fall from the atmosphere and reach the
surface.
PRECIPITATION RADAR WEATHER DESCRIPTIONS
Existing radar systems cannot detect turbulence. However, there is a direct correlation between the degree
of turbulence and other weather features associated with thunderstorms and the weather radar precipitation
intensity. Controllers will issue (where capable) precipitation intensity as observed by radar when using
weather and radar processor (WARP) or NAS ground based digital radars with weather capabilities. When
precipitation intensity information is not available, the intensity will be described as UNKNOWN. When
intensity levels can be determined, they shall be described as:
A standard instrument approach procedure in which an electronic glideslope/or other type of glidepath is
provided; e.g., ILS, PAR, and GLS. (See INSTRUMENT LANDING SYSTEM.)
(See PRECISION APPROACH RADAR.)
PRECISION APPROACH RADAR
Radar equipment in some ATC facilities operated by the FAA and/or the military services at joint-use
civil/military locations and separate military installations to detect and display azimuth, elevation, and
range of aircraft on the final approach course to a runway. This equipment may be used to monitor certain
nonradar approaches, but is primarily used to conduct a precision instrument approach (PAR) wherein the
controller issues guidance instructions to the pilot based on the aircraft's position in relation to the
final approach course (azimuth), the glidepath (elevation), and the distance (range) from the touchdown
point on the runway as displayed on the radar scope.
(See GLIDEPATH.) (See PAR.) (See ICAO term PRECISION APPROACH
RADAR.) (Refer to
AIM.)
[ICAO] Primary radar equipment used to determine the position of an aircraft during final approach, in terms
of lateral and vertical deviations relative to a nominal approach path, and in range relative to touchdown.
PRECISION OBSTACLE FREE ZONE (POFZ)
An 800 foot wide by 200 foot long area centered on the runway centerline adjacent to the threshold designed
to protect aircraft flying precision approaches from ground vehicles and other aircraft when ceiling is less
than 250 feet or visibility is less than 3/4 statute mile (or runway visual range below 4,000 feet.)
PRECISION RUNWAY MONITOR (PRM) SYSTEM
Provides air traffic controllers monitoring the NTZ during simultaneous close parallel PRM approaches with
precision, high update rate secondary surveillance data. The high update rate surveillance sensor component
of the PRM system is only required for specific runway or approach course separation. The high resolution
color monitoring display, Final Monitor Aid (FMA) of the PRM system, or other FMA with the same capability,
presents (NTZ) surveillance track data to controllers along with detailed maps depicting approaches and no
transgression zone and is required for all simultaneous close parallel PRM NTZ monitoring operations. (Refer
to
AIM.)
PREDICTIVE WIND SHEAR ALERT SYSTEM (PWS)
A self contained system used onboard some aircraft to alert the flight crew to the presence of a potential
wind shear. PWS systems typically monitor 3 miles ahead and 25 degrees left and right of the aircraft's
heading at or below 1200' AGL. Departing flights may receive a wind shear alert after they start the takeoff
roll and may elect to abort the takeoff. Aircraft on approach receiving an alert may elect to go around or
perform a wind shear escape maneuver.
An instrument approach procedure titled ILS PRM, RNAV PRM, LDA PRM, or GLS PRM conducted to parallel runways
separated by less than 4,300 feet and at least 3,000 feet where independent closely spaced approaches are
permitted. Use of an enhanced display with alerting, a No Transgression Zone (NTZ), secondary monitor
frequency, pilot PRM training, and publication of an Attention All Users Page are required for all PRM
approaches. Depending on the runway spacing, the approach courses may be parallel or one approach course
must be offset. PRM procedures are also used to conduct Simultaneous Offset Instrument Approach (SOIA)
operations. In SOIA, one straight-in ILS PRM, RNAV PRM, GLS PRM, and one offset LDA PRM, RNAV PRM or GLS PRM
approach are utilized. PRM procedures are terminated and a visual segment begins at the offset approach
missed approach point where the minimum distance between the approach courses is 3000 feet. Runway spacing
can be as close as 750 feet. (Refer to
AIM.)
PROCEDURAL CONTROL [ICAO]
Term used to indicate that information derived from an ATS surveillance system is not required for the
provision of air traffic control service.
PROCEDURAL SEPARATION [ICAO]
The separation used when providing procedural control.
PROCEDURE TURN
The maneuver prescribed when it is necessary to reverse direction to establish an aircraft on the
intermediate approach segment or final approach course. The outbound course, direction of turn, distance
within which the turn must be completed, and minimum altitude are specified in the procedure. However,
unless otherwise restricted, the point at which the turn may be commenced and the type and rate of turn are
left to the discretion of the pilot.
[ICAO] A maneuver in which a turn is made away from a designated track followed by a turn in the opposite
direction to permit the aircraft to intercept and proceed along the reciprocal of the designated track.
Note 1: Procedure turns are designated "left" or "right" according to the direction of the initial turn.
Note 2: Procedure turns may be designated as being made either in level flight or while descending,
according to the circumstances of each individual approach procedure.
PROCEDURE TURN INBOUND
That point of a procedure turn maneuver where course reversal has been completed and an aircraft is
established inbound on the intermediate approach segment or final approach course. A report of "procedure
turn inbound" is normally used by ATC as a position report for separation purposes. (See FINAL APPROACH COURSE.) (See PROCEDURE
TURN.) (See SEGMENTS OF AN INSTRUMENT APPROACH
PROCEDURE.)
PROFILE DESCENT
An uninterrupted descent (except where level flight is required for speed adjustment; e.g., 250 knots at
10,000 feet MSL) from cruising altitude/level to interception of a glideslope or to a minimum altitude
specified for the initial or intermediate approach segment of a nonprecision instrument approach. The
profile descent normally terminates at the approach gate or where the glideslope or other appropriate
minimum altitude is intercepted.
[ICAO] An airspace of defined dimensions, above the land areas or territorial waters of a State, within
which the flight of aircraft is prohibited.
PROMINENT OBSTACLE
An obstacle that meets one or more of the following conditions:
An obstacle which stands out beyond the adjacent surface of surrounding terrain and immediately projects
a noticeable hazard to aircraft in flight.
An obstacle, not characterized as low and close in, whose height is no less than 300 feet above the
departure end of takeoff runway (DER) elevation, is within 10NM from the DER, and that penetrates that
airport/heliport's diverse departure obstacle clearance surface (OCS).
An obstacle beyond 10NM from an airport/heliport that requires an obstacle departure procedure (ODP) to
ensure obstacle avoidance.
Each center has a PBCT parameter for each internal airport. Proposed internal flight plans are transmitted
to the adjacent center if the flight time along the proposed route from the departure airport to the center
boundary is less than or equal to the value of PBCT or if airport adaptation specifies transmission
regardless of PBCT.
PROPOSED DEPARTURE TIME
The time that the aircraft expects to become airborne.
PROTECTED AIRSPACE
The airspace on either side of an oceanic route/track that is equal to one-half the lateral separation
minimum except where reduction of protected airspace has been authorized.
PROTECTED SEGMENT
The protected segment is a segment on the amended TFM route that is to be inhibited from automatic adapted
route alteration by ERAM.
A UAS operation meeting the qualifications and conditions required for the operation of a public aircraft.
(See AC-1.1) (See AIM)
PUBLISHED INSTRUMENT APPROACH PROCEDURE VISUAL SEGMENT
A segment on an IAP chart annotated as "Fly Visual to Airport" or "Fly Visual." A dashed arrow will indicate
the visual flight path on the profile and plan view with an associated note on the approximate heading and
distance. The visual segment should be flown as a dead reckoning course while maintaining visual conditions.
PUBLISHED ROUTE
A route for which an IFR altitude has been established and published; e.g., Federal Airways, Jet Routes,
Area Navigation Routes, Specified Direct Routes.
'Q' is the designator assigned to published RNAV routes used by the United States.
QFE
The atmospheric pressure at aerodrome elevation (or at runway threshold).
QNE
The barometric pressure used for the standard altimeter setting (29.92 inches Hg.).
QNH
The barometric pressure as reported by a particular station.
QUADRANT
A quarter part of a circle, centered on a NAVAID, oriented clockwise from magnetic north as follows: NE
quadrant 000-089, SE quadrant 090-179, SW quadrant 180-269, NW quadrant 270-359.
A feature of the EAS and STARS which provides the controller the capability to display full data blocks of
tracked aircraft from other control positions.
A device that provides information on range, azimuth, and/or elevation of objects by measuring the time
interval between transmission and reception of directional radio pulses and correlating the angular
orientation of the radiated antenna beam or beams in azimuth and/or elevation.
Primary Radar A radar system in which a minute portion of a radio pulse transmitted from a site
is reflected by an object and then received back at that site for processing and display at an air
traffic control facility.
Secondary Radar/Radar Beacon (ATCRBS) A radar system in which the object to be detected is
fitted with cooperative equipment in the form of a radio receiver/transmitter (transponder). Radar
pulses transmitted from the searching transmitter/receiver (interrogator) site are received in the
cooperative equipment and used to trigger a distinctive transmission from the transponder. This reply
transmission, rather than a reflected signal, is then received back at the transmitter/receiver site for
processing and display at an air traffic control facility. (COOPERATIVE SURVEILLANCE.) (See INTERROGATOR.) (NON-COOPERATIVE
SURVEILLANCE.) (See TRANSPONDER.) (Refer to
AIM.)
[ICAO] A radio detection device which provides information on range, azimuth and/or elevation of objects.
Primary Radar Radar system which uses reflected radio signals.
Secondary Radar Radar system wherein a radio signal transmitted from a radar station initiates the
transmission of a radio signal from another station.
RADAR ADVISORY
The provision of advice and information based on radar observations. (See ADVISORY
SERVICE.)
[ICAO] An approach, executed by an aircraft, under the direction of a radar controller.
RADAR APPROACH CONTROL FACILITY
A terminal ATC facility that uses radar and nonradar capabilities to provide approach control services to
aircraft arriving, departing, or transiting airspace controlled by the facility. (See APPROACH CONTROL SERVICE.)
Provides radar ATC services to aircraft operating in the vicinity of one or more civil and/or military
airports in a terminal area. The facility may provide services of a ground controlled approach (GCA);
i.e., ASR and PAR approaches. A radar approach control facility may be operated by FAA, USAF, US Army,
USN, USMC, or jointly by FAA and a military service. Specific facility nomenclatures are used for
administrative purposes only and are related to the physical location of the facility and the operating
service generally as follows:
Army Radar Approach Control (ARAC) (Army).
Radar Air Traffic Control Facility (RATCF) (Navy/FAA).
Radar Approach Control (RAPCON) (Air Force/FAA).
Terminal Radar Approach Control (TRACON) (FAA).
Airport Traffic Control Tower (ATCT) (FAA). (Only those towers delegated approach control
authority.)
RADAR ARRIVAL
An aircraft arriving at an airport served by a radar facility and in radar contact with the facility. (See NONRADAR.)
The visual indication on a radar display of unwanted signals.
RADAR CONTACT
Used by ATC to inform an aircraft that it is identified using an approved ATC surveillance source on an
air traffic controller's display and that radar flight following will be provided until radar service is
terminated. Radar service may also be provided within the limits of necessity and capability. When a
pilot is informed of "radar contact," he/she automatically discontinues reporting over compulsory
reporting points. (See ATC SURVEILLANCE SOURCE.) (See RADAR CONTACT LOST.) (See RADAR
FLIGHT FOLLOWING.) (See RADAR SERVICE.) (See RADAR SERVICE TERMINATED.) (Refer to
AIM.)
The term used to inform the controller that the aircraft is identified and approval is granted for the
aircraft to enter the receiving controllers airspace. (See ICAO term RADAR CONTACT.)
[ICAO] The situation which exists when the radar blip or radar position symbol of a particular aircraft is
seen and identified on a radar display.
RADAR CONTACT LOST
Used by ATC to inform a pilot that the surveillance data used to determine the aircraft's position is no
longer being received, or is no longer reliable and radar service is no longer being provided. The loss may
be attributed to several factors including the aircraft merging with weather or ground clutter, the aircraft
operating below radar line of sight coverage, the aircraft entering an area of poor radar return, failure of
the aircraft's equipment, or failure of the surveillance equipment. (See CLUTTER.)
(See RADAR CONTACT.)
The observation of the progress of radar identified aircraft, whose primary navigation is being provided by
the pilot, wherein the controller retains and correlates the aircraft identity with the appropriate target
or target symbol displayed on the radar scope. (See RADAR CONTACT.) (See RADAR SERVICE.) (Refer to
AIM.)
RADAR IDENTIFICATION
The process of ascertaining that an observed radar target is the radar return from a particular aircraft.
(See RADAR CONTACT.) (See RADAR SERVICE.)
RADAR IDENTIFIED AIRCRAFT
An aircraft, the position of which has been correlated with an observed target or symbol on the radar
display. (See RADAR CONTACT.) (See RADAR CONTACT
LOST.)
An action taken by a controller to transfer the radar identification of an aircraft to another controller if
the aircraft will or may enter the airspace or protected airspace of another controller and radio
communications will not be transferred.
RADAR REQUIRED
A term displayed on charts and approach plates and included in FDC NOTAMs to alert pilots that segments of
either an instrument approach procedure or a route are not navigable because of either the absence or
unusability of a NAVAID. The pilot can expect to be provided radar navigational guidance while transiting
segments labeled with this term. (See RADAR ROUTE.) (See
RADAR SERVICE.)
RADAR ROUTE
A flight path or route over which an aircraft is vectored. Navigational guidance and altitude assignments
are provided by ATC. (See FLIGHT PATH.) (See ROUTE.)
A term which encompasses one or more of the following services based on the use of radar which can be
provided by a controller to a pilot of a radar identified aircraft.
Radar Monitoring: The radar flight-following of aircraft, whose primary navigation is being performed by
the pilot, to observe and note deviations from its authorized flight path, airway, or route. When being
applied specifically to radar monitoring of instrument approaches; i.e., with precision approach radar
(PAR) or radar monitoring of simultaneous ILS,RNAV and GLS approaches, it includes advice and
instructions whenever an aircraft nears or exceeds the prescribed PAR safety limit or simultaneous ILS
RNAV and GLS no transgression zone. (See ADDITIONAL SERVICES.) (See TRAFFIC ADVISORIES.)
Radar Navigational Guidance: Vectoring aircraft to provide course guidance.
Radar Separation: Radar spacing of aircraft in accordance with established minima.
[ICAO] Term used to indicate a service provided directly by means of radar.
Monitoring The use of radar for the purpose of providing aircraft with information and advice relative
to significant deviations from nominal flight path.
Separation The separation used when aircraft position information is derived from radar sources.
RADAR SERVICE TERMINATED
Used by ATC to inform a pilot that he/she will no longer be provided any of the services that could be
received while in radar contact. Radar service is automatically terminated, and the pilot is not advised in
the following cases:
An aircraft cancels its IFR flight plan, except within Class B airspace, Class C airspace, a TRSA, or
where Basic Radar service is provided.
An aircraft conducting an instrument, visual, or contact approach has landed or has been instructed to
change to advisory frequency.
An arriving VFR aircraft, receiving radar service to a tower-controlled airport within Class B airspace,
Class C airspace, a TRSA, or where sequencing service is provided, has landed; or to all other airports,
is instructed to change to tower or advisory frequency.
An aircraft completes a radar approach.
RADAR SURVEILLANCE
The radar observation of a given geographical area for the purpose of performing some radar function.
RADAR TRAFFIC ADVISORIES
Advisories issued to alert pilots to known or observed radar traffic which may affect the intended route of
flight of their aircraft. (See TRAFFIC ADVISORIES.)
An aircraft navigational instrument coupled with a gyro compass or similar compass that indicates the
direction of a selected NAVAID and indicates bearing with respect to the heading of the aircraft.
A technique whereby a civil GNSS receiver/processor determines the integrity of the GNSS navigation signals
without reference to sensors or non-DoD integrity systems other than the receiver itself. This determination
is achieved by a consistency check among redundant pseudorange measurements.
RECEIVING CONTROLLER
A controller/facility receiving control of an aircraft from another controller/facility.
RVSM airspace is defined as any airspace between FL 290 and FL 410 inclusive, where eligible aircraft are
separated vertically by 1,000 feet. Authorization guidance for operations in this airspace is provided in
Advisory Circular AC 91-85.
A departure time restriction issued to a pilot by ATC (either directly or through an authorized relay) when
necessary to separate a departing aircraft from other traffic.
[ICAO] Time prior to which an aircraft should be given further clearance or prior to which it should not
proceed in case of radio failure.
REMOTE AIRPORT INFORMATION SERVICE (RAIS)
A temporary service provided by facilities, which are not located on the landing airport, but have
communication capability and automated weather reporting available to the pilot at the landing airport.
REMOTE COMMUNICATIONS AIR/GROUND FACILITY
An unmanned VHF/UHF transmitter/receiver facility which is used to expand ARTCC air/ground communications
coverage and to facilitate direct contact between pilots and controllers. RCAG facilities are sometimes not
equipped with emergency frequencies 121.5 MHz and 243.0 MHz. (Refer to
AIM.)
REMOTE COMMUNICATIONS OUTLET
An unmanned communications facility remotely controlled by air traffic personnel. RCOs serve FSSs. RTRs
serve terminal ATC facilities. An RCO or RTR may be UHF or VHF and will extend the communication range of
the air traffic facility. There are several classes of RCOs and RTRs. The class is determined by the number
of transmitters or receivers. Classes A through G are used primarily for air/ground purposes. RCO and RTR
class O facilities are nonprotected outlets subject to undetected and prolonged outages. RCO (O's) and RTR
(O's) were established for the express purpose of providing ground-to-ground communications between air
traffic control specialists and pilots located at a satellite airport for delivering en route clearances,
issuing departure authorizations, and acknowledging instrument flight rules cancellations or
departure/landing times. As a secondary function, they may be used for advisory purposes whenever the
aircraft is below the coverage of the primary air/ground frequency.
REMOTE IDENTIFICATION (RID)
A system for electronic identification and secure oversight of UAS. (See 4 CFR Part 89) (See AIM)
REMOTE PILOT
Pilot of a UAS who is not operating as a recreational flyer under 49 USC §44809, the Exception for Limited
Recreational Operations of Unmanned Aircraft.
REMOTE PILOT IN COMMAND (RPIC)
The RPIC is directly responsible for and is the final authority as to the operation of the unmanned aircraft
system.
Used to instruct pilots to advise ATC of specified information; e.g., "Report passing Hamilton VOR."
REPORTING POINT
A geographical location in relation to which the position of an aircraft is reported. (See COMPULSORY
REPORTING POINTS.) (See ICAO term REPORTING POINT.) (Refer to
AIM.)
[ICAO] A specified geographical location in relation to which the position of an aircraft can be reported.
REQUEST FULL ROUTE CLEARANCE
Used by pilots to request that the entire route of flight be read verbatim in an ATC clearance. Such request
should be made to preclude receiving an ATC clearance based on the original filed flight plan when a filed
IFR flight plan has been revised by the pilot, company, or operations prior to departure.
REQUIRED NAVIGATION PERFORMANCE (RNP)
A statement of the navigational performance necessary for operation within a defined airspace. The following
terms are commonly associated with RNP:
Required Navigation Performance Level or Type (RNP-X). A value, in nautical miles (NM), from the
intended horizontal position within which an aircraft would be at least 95-percent of the total flying
time.
Required Navigation Performance (RNP) Airspace. A generic term designating airspace, route(s), leg(s),
operation(s), or procedure(s) where minimum required navigational performance (RNP) have been
established.
Actual Navigation Performance (ANP). A measure of the current estimated navigational performance. Also
referred to as Estimated Position Error (EPE).
Estimated Position Error (EPE). A measure of the current estimated navigational performance. Also
referred to as Actual Navigation Performance (ANP).
Lateral Navigation (LNAV). A function of area navigation (RNAV) equipment which calculates, displays,
and provides lateral guidance to a profile or path.
Vertical Navigation (VNAV). A function of area navigation (RNAV) equipment which calculates, displays,
and provides vertical guidance to a profile or path.
REROUTE IMPACT ASSESSMENT (RRIA)
A capability within the Traffic Flow Management System that is used to define and evaluate a potential
reroute prior to implementation, with or without miles-in-trail (MIT) restrictions. RRIA functions estimate
the impact on demand (e.g.,sector loads) and performance (e.g., flight delay). Using RRIA, traffic
management personnel can determine whether the reroute will sufficiently reduce demand in the Flow
Constraint Area and not create excessive "spill over" demand in the adjacent airspace on a specific route
segment or point of interest (POI).
RESCUE COORDINATION CENTER
A search and rescue (SAR) facility equipped and manned to coordinate and control SAR operations in an area
designated by the SAR plan. The U.S. Coast Guard and the U.S. Air Force have responsibility for the
operation of RCCs. (See ICAO term RESCUE COORDINATION CENTRE.)
RESCUE COORDINATION CENTRE [ICAO]
A unit responsible for promoting efficient organization of search and rescue service and for coordinating
the conduct of search and rescue operations within a search and rescue region.
RESOLUTION ADVISORY
A display indication given to the pilot by the traffic alert and collision avoidance systems (TCAS II)
recommending a maneuver to increase vertical separation relative to an intruding aircraft. Positive,
negative, and vertical speed limit (VSL) advisories constitute the resolution advisories. A resolution
advisory is also classified as corrective or preventive.
[ICAO] An airspace of defined dimensions, above the land areas or territorial waters of a State, within
which the flight of aircraft is restricted in accordance with certain specified conditions.
RESUME NORMAL SPEED
Used by ATC to advise a pilot to resume an aircraft's normal operating speed. It is issued to terminate a
speed adjustment where no published speed restrictions apply. It does not delete speed restrictions in
published procedures of upcoming segments of flight. This does not relieve the pilot of those speed
restrictions, which are applicable to 14 CFR Section 91.117.
RESUME OWN NAVIGATION
Used by ATC to advise a pilot to resume his/her own navigational responsibility. It is issued after
completion of a radar vector or when radar contact is lost while the aircraft is being radar vectored. (See RADAR CONTACT LOST.) (See RADAR
SERVICE TERMINATED.)
RESUME PUBLISHED SPEED
Used by ATC to advise a pilot to resume published speed restrictions that are applicable to a SID, STAR, or
other instrument procedure. It is issued to terminate a speed adjustment where speed restrictions are
published on a charted procedure.
An RVFP is a special visual flight procedure flown on an IFR flight plan. It is flown in visual conditions
and clear of clouds must be maintained. An RVFP is flown using an approved RNAV system to maintain published
lateral and vertical paths to runways without an instrument approach procedure. It requires an ATC clearance
and may begin at other points along the path of the charted procedure when approved by ATC. An RVFP is not
published in the Federal Register for public use and the operator is required to have a specific Operations
Specification approval. Required ceiling and visibility minima are published on the procedure chart. An RVFP
does not have a missed approach procedure and is not evaluated for obstacle protection.
ROAD RECONNAISSANCE
Military activity requiring navigation along roads, railroads, and rivers. Reconnaissance route/route
segments are seldom along a straight line and normally require a lateral route width of 10 NM to 30 NM and
an altitude range of 500 feet to 10,000 feet AGL.
ROGER
I have received all of your last transmission. It should not be used to answer a question requiring a yes or
a no answer. (See AFFIRMATIVE.) (See NEGATIVE.)
A phenomenon resulting from the vertical down wash of air generated by the main rotor(s) of a helicopter.
ROUND-ROBIN FLIGHT PLAN
A single flight plan filed from the departure airport to an intermediary destination(s) and then returning
to the original departure airport.
ROUTE
A defined path, consisting of one or more courses in a horizontal plane, which aircraft traverse over the
surface of the earth. (See AIRWAY.) (See JET ROUTE.) (See PUBLISHED ROUTE.) (See UNPUBLISHED ROUTE.)
A capability within the Traffic Flow Management System that allows traffic management personnel to submit or
edit a route amendment for one or more flights.
ROUTE SEGMENT
As used in Air Traffic Control, a part of a route that can be defined by two navigational fixes, two
NAVAIDs, or a fix and a NAVAID. (See FIX.) (See ROUTE.) (See ICAO
term ROUTE SEGMENT.)
[ICAO] A portion of a route to be flown, as defined by two consecutive significant points specified in a
flight plan.
A defined rectangular area on a land airport prepared for the landing and takeoff run of aircraft along its
length. Runways are normally numbered in relation to their magnetic direction rounded off to the nearest 10
degrees; e.g., Runway 1, Runway 25. (See PARALLEL RUNWAYS.)
[ICAO] A defined rectangular area on a land aerodrome prepared for the landing and take-off of aircraft.
Numerical readings, provided by airport operators, that indicate runway surface contamination (for example,
slush, ice, rain, etc.). These values range from "1" (poor) to "6" (dry) and must be included on the ATIS
when the reportable condition is less than 6 in any one or more of the three runway zones (touchdown,
midpoint, rollout).
RUNWAY CONDITION READING
Numerical decelerometer readings relayed by air traffic controllers at USAF and certain civil bases for use
by the pilot in determining runway braking action. These readings are routinely relayed only to USAF and Air
National Guard Aircraft. (See BRAKING ACTION.)
RUNWAY CONDITION REPORT (RwyCR)
A data collection worksheet used by airport operators that correlates the runway percentage of coverage
along with the depth and type of contaminant for the purpose of creating a FICON NOTAM.
(See RUNWAY CONDITION CODES.)
An array of red lights which include the first light at the hold line followed by a series of evenly spaced
lights to the runway edge aligned with the taxiway centerline, and one additional light at the runway
centerline in line with the last two lights before the runway edge.
RUNWAY GRADIENT
The average slope, measured in percent, between two ends or points on a runway. Runway gradient is depicted
on Government aerodrome sketches when total runway gradient exceeds 0.3%.
RUNWAY HEADING
The magnetic direction that corresponds with the runway centerline extended, not the painted runway number.
When cleared to "fly or maintain runway heading," pilots are expected to fly or maintain the heading that
corresponds with the extended centerline of the departure runway. Drift correction shall not be applied;
e.g., Runway 4, actual magnetic heading of the runway centerline 044, fly 044.
RUNWAY IN USE/ACTIVE RUNWAY/DUTY RUNWAY
Any runway or runways currently being used for takeoff or landing. When multiple runways are used, they are
all considered active runways. In the metering sense, a selectable adapted item which specifies the landing
runway configuration or direction of traffic flow. The adapted optimum flight plan from each transition fix
to the vertex is determined by the runway configuration for arrival metering processing purposes.
In military aviation exclusively, a stabilized or paved area beyond the end of a runway, of the same width
as the runway plus shoulders, centered on the extended runway centerline.
RUNWAY PROFILE DESCENT
An instrument flight rules (IFR) air traffic control arrival procedure to a runway published for pilot use
in graphic and/or textual form and may be associated with a STAR. Runway Profile Descents provide routing
and may depict crossing altitudes, speed restrictions, and headings to be flown from the en route structure
to the point where the pilot will receive clearance for and execute an instrument approach procedure. A
Runway Profile Descent may apply to more than one runway if so stated on the chart. (Refer to
AIM.)
RUNWAY SAFETY AREA
A defined surface surrounding the runway prepared, or suitable, for reducing the risk of damage to airplanes
in the event of an undershoot, overshoot, or excursion from the runway. The dimensions of the RSA vary and
can be determined by using the criteria contained within AC 150/5300-13, Airport Design, Chapter 3. Figure
31 in AC 150/5300-13 depicts the RSA. The design standards dictate that the RSA shall be:
Cleared, graded, and have no potentially hazardous ruts, humps, depressions, or other surface
variations;
Drained by grading or storm sewers to prevent water accumulation;
Capable, under dry conditions, of supporting snow removal equipment, aircraft rescue and firefighting
equipment, and the occasional passage of aircraft without causing structural damage to the aircraft;
and,
Free of objects, except for objects that need to be located in the runway safety area because of their
function. These objects shall be constructed on low impact resistant supports (frangible mounted
structures) to the lowest practical height with the frangible point no higher than 3 inches above grade.
(Refer to AC 150/5300-13, Airport Design, Chapter 3.)
RUNWAY STATUS LIGHTS (RWSL) SYSTEM
The RWSL is a system of runway and taxiway lighting to provide pilots increased situational awareness by
illuminating runway entry lights (REL) when the runway is unsafe for entry or crossing, and take-off hold
lights (THL) when the runway is unsafe for departure.
A noise abatement runway selection plan designed to enhance noise abatement efforts with regard to airport
communities for arriving and departing aircraft. These plans are developed into runway use programs and
apply to all turbojet aircraft 12,500 pounds or heavier; turbojet aircraft less than 12,500 pounds are
included only if the airport proprietor determines that the aircraft creates a noise problem. Runway use
programs are coordinated with FAA offices, and safety criteria used in these programs are developed by the
Office of Flight Operations. Runway use programs are administered by the Air Traffic Service as "Formal" or
"Informal" programs.
Formal Runway Use Program An approved noise abatement program which is defined and acknowledged in a
Letter of Understanding between Flight Operations, Air Traffic Service, the airport proprietor, and the
users. Once established, participation in the program is mandatory for aircraft operators and pilots as
provided for in 14 CFR Section 91.129.
Informal Runway Use Program An approved noise abatement program which does not require a Letter of
Understanding, and participation in the program is voluntary for aircraft operators/pilots.
A safety alert issued by ATC to aircraft under their control if ATC is aware the aircraft is at an altitude
which, in the controller's judgment, places the aircraft in unsafe proximity to terrain, obstructions, or
other aircraft. The controller may discontinue the issuance of further alerts if the pilot advises he/she is
taking action to correct the situation or has the other aircraft in sight.
Terrain/Obstruction Alert: A safety alert issued by ATC to aircraft under their control if ATC
is aware the aircraft is at an altitude which, in the controller's judgment, places the aircraft in
unsafe proximity to terrain/obstructions; e.g., "Low Altitude Alert, check your altitude immediately."
Aircraft Conflict Alert: A safety alert issued by ATC to aircraft under their control if ATC is
aware of an aircraft that is not under their control at an altitude which, in the controller's judgment,
places both aircraft in unsafe proximity to each other. With the alert, ATC will offer the pilot an
alternate course of action when feasible; e.g., "Traffic Alert, advise you turn right heading zero niner
zero or climb to eight thousand immediately."
Note: The issuance of a safety alert is contingent upon the capability of the controller to have an
awareness of an unsafe condition. The course of action provided will be predicated on other traffic under
ATC control. Once the alert is issued, it is solely the pilot's prerogative to determine what course of
action, if any, he/she will take.
SAFETY LOGIC SYSTEM
A software enhancement to ASDE-3, ASDE-X, and ASSC, that predicts the path of aircraft landing and/or
departing, and/or vehicular movements on runways. Visual and aural alarms are activated when the safety
logic projects a potential collision. The Airport Movement Area Safety System (AMASS) is a safety logic
system enhancement to the ASDE3. The Safety Logic System for ASDE-X and ASSC is an integral part of the
software program.
SAFETY LOGIC SYSTEM ALERTS
ALERT: An actual situation involving two real safety logic tracks (aircraft/aircraft,
aircraft/vehicle, or aircraft/other tangible object) that safety logic has predicted will result in an
imminent collision, based upon the current set of Safety Logic parameters.
FALSE ALERT:
Alerts generated by one or more false surface radar targets that the system has interpreted as real
tracks and placed into safety logic.
Alerts in which the safety logic software did not perform correctly, based upon the design
specifications and the current set of Safety Logic parameters.
The alert is generated by surface radar targets caused by moderate or greater precipitation.
NUISANCE ALERT: An alert in which one or more of the following is true:
The alert is generated by a known situation that is not considered an unsafe operation, such as
LAHSO or other approved operations.
The alert is generated by inaccurate secondary radar data received by the Safety Logic System.
One or more of the aircraft involved in the alert is not intending to use a runway (for example,
helicopter, pipeline patrol, non-Mode C overflight, etc.).
VALID NONALERT: A situation in which the safety logic software correctly determines that an
alert is not required, based upon the design specifications and the current set of Safety Logic
parameters.
INVALID NONALERT: A situation in which the safety logic software did not issue an alert when an
alert was required, based upon the design specifications.
SAIL BACK
A maneuver during high wind conditions (usually with power off) where float plane movement is controlled by
water rudders/opening and closing cabin doors.
SAME DIRECTION AIRCRAFT
Aircraft are operating in the same direction when:
They are following the same track in the same direction; or
Their tracks are parallel and the aircraft are flying in the same direction; or
Their tracks intersect at an angle of less than 45 degrees.
Used to request a repeat of the last transmission. Usually specifies transmission or portion thereof not
understood or received; e.g., "Say again all after ABRAM VOR."
SAY ALTITUDE
Used by ATC to ascertain an aircraft's specific altitude/flight level. When the aircraft is climbing or
descending, the pilot should state the indicated altitude rounded to the nearest 100 feet.
SAY HEADING
Used by ATC to request an aircraft heading. The pilot should state the actual heading of the aircraft.
SCHEDULED TIME OF ARRIVAL (STA)
A STA is the desired time that an aircraft should cross a certain point (landing or metering fix). It takes
other traffic and airspace configuration into account. A STA time shows the results of the TBFM scheduler
that has calculated an arrival time according to parameters such as optimized spacing, aircraft performance,
and weather.
A designated portion of water outlined by visual surface markers for and intended to be used by aircraft
designed to operate on water.
SEARCH AND RESCUE
A service which seeks missing aircraft and assists those found to be in need of assistance. It is a
cooperative effort using the facilities and services of available Federal, state and local agencies. The
U.S. Coast Guard is responsible for coordination of search and rescue for the Maritime Region, and the U.S.
Air Force is responsible for search and rescue for the Inland Region. Information pertinent to search and
rescue should be passed through any air traffic facility or be transmitted directly to the Rescue
Coordination Center by telephone. (See FLIGHT SERVICE STATION.) (See RESCUE COORDINATION CENTER.) (Refer to
AIM.)
SEARCH AND RESCUE FACILITY
A facility responsible for maintaining and operating a search and rescue (SAR) service to render aid to
persons and property in distress. It is any SAR unit, station, NET, or other operational activity which can
be usefully employed during an SAR Mission; e.g., a Civil Air Patrol Wing, or a Coast Guard Station. (See SEARCH AND RESCUE.)
A parameter number of minutes after the meter fix time when arrival aircraft will be deleted from the
arrival sector list.
SECURITY NOTICE (SECNOT)
A SECNOT is a request originated by the Air Traffic Security Coordinator (ATSC) for an extensive
communications search for aircraft involved, or suspected of being involved, in a security violation, or are
considered a security risk. A SECNOT will include the aircraft identification, search area, and expiration
time. The search area, as defined by the ATSC, could be a single airport, multiple airports, a radius of an
airport or fix, or a route of flight. Once the expiration time has been reached, the SECNOT is considered to
be canceled.
SECURITY SERVICES AIRSPACE
Areas established through the regulatory process or by NOTAM, issued by the Administrator under title 14,
CFR, sections 99.7, 91.141, and 91.139, which specify that ATC security services are required; i.e., ADIZ or
temporary flight rules areas.
SEE AND AVOID
When weather conditions permit, pilots operating IFR or VFR are required to observe and maneuver to avoid
other aircraft. Right-of-way rules are contained in
14 CFR Part 91.
SEGMENTED CIRCLE
A system of visual indicators designed to provide traffic pattern information at airports without operating
control towers. (Refer to
AIM.)
SEGMENTS OF A SID/STAR
En Route Transition- The segment(s) of a SID/STAR that connect to/from en route flight. Not all
SIDs/STARs will contain an en route transition.
En Route Transition Waypoint- The NAVAID/fix/waypoint that defines the beginning of the SID/STAR en
route transition.
Common Route- The segment(s) of a SID/STAR procedure that provides a single route serving an
airport/runway or multiple airports/runways. The common route may consist of a single point. Not all
conventional SIDs will contain a common route.
Runway Transition- The segment(s) of a SID/STAR between the common route/point and the runway(s). Not
all SIDs/STARs will contain a runway transition.
Runway Transition Waypoint (RTW)- On a STAR, the NAVAID/fix/waypoint that defines the end of the common
route or en route transition and the beginning of a runway transition (In the arrival route description
found on the STAR chart, the last fix of the common route and the first fix of the runway
transition(s)).
SEGMENTS OF AN INSTRUMENT APPROACH PROCEDURE
An instrument approach procedure may have as many as four separate segments depending on how the approach
procedure is structured.
Initial Approach: The segment between the initial approach fix and the intermediate fix or the
point where the aircraft is established on the intermediate course or final approach course. (See ICAO
term INITIAL APPROACH SEGMENT.)
Intermediate Approach: The segment between the intermediate fix or point and the final approach
fix. (See ICAO term INTERMEDIATE APPROACH SEGMENT.)
Final Approach: The segment between the final approach fix or point and the runway, airport, or
missed approach point. (See ICAO term FINAL APPROACH SEGMENT.)
Missed Approach: The segment between the missed approach point or the point of arrival at
decision height and the missed approach fix at the prescribed altitude. (Refer to
14 CFR Part 97.) (See ICAO term
MISSED APPROACH PROCEDURE.)
SELF-BRIEFING
A self-briefing is a review, using automated tools, of all meteorological and aeronautical information that
may influence the pilot in planning, altering, or canceling a proposed route of flight.
SENSE AND AVOID (SAA)
The capability of an unmanned aircraft to detect (sense) and avoid collisions with other aircraft and all
obstacles, whether airborne or on the ground while operating in the NAS.
SEPARATION
In air traffic control, the spacing of aircraft to achieve their safe and orderly movement in flight and
while landing and taking off. (See SEPARATION MINIMA.)
[ICAO] Spacing between aircraft, levels or tracks.
SEPARATION MINIMA
The minimum longitudinal, lateral, or vertical distances by which aircraft are spaced through the
application of air traffic control procedures. (See SEPARATION.)
SERVICE
A generic term that designates functions or assistance available from or rendered by air traffic control.
For example, Class C service would denote the ATC services provided within a Class C airspace area.
SEVERE WEATHER AVOIDANCE PLAN
An approved plan to minimize the affect of severe weather on traffic flows in impacted terminal and/or ARTCC
areas. SWAP is normally implemented to provide the least disruption to the ATC system when flight through
portions of airspace is difficult or impossible due to severe weather.
SEVERE WEATHER FORECAST ALERTS
Preliminary messages issued in order to alert users that a Severe Weather Watch Bulletin (WW) is being
issued. These messages define areas of possible severe thunderstorms or tornado activity. The messages are
unscheduled and issued as required by the Storm Prediction Center (SPC) at Norman, Oklahoma. (See AIRMET.) (See CONVECTIVE SIGMET.) (See CWA.) (See GRAPHICAL AIRMEN'S METEOROLOGICAL INFORMATION.) (See
SIGMET.)
A clearance issued to a departing IFR flight which authorizes IFR flight to a specific fix short of the
destination while air traffic control facilities are coordinating and obtaining the complete clearance.
SHORT TAKEOFF AND LANDING AIRCRAFT
An aircraft which, at some weight within its approved operating weight, is capable of operating from a
runway in compliance with the applicable STOL characteristics, airworthiness, operations, noise, and
pollution standards. (See VERTICAL TAKEOFF AND LANDING
AIRCRAFT.)
A visual maneuver accomplished by a pilot at the completion of an instrument approach to permit a
straight-in landing on a parallel runway not more than 1,200 feet to either side of the runway to which the
instrument approach was conducted. (Refer to
AIM.)
SIGMET
A weather advisory issued concerning weather significant to the safety of all aircraft. SIGMET advisories
cover severe and extreme turbulence, severe icing, and widespread dust or sandstorms that reduce visibility
to less than 3 miles. (See AIRMET.) (See AWW.) (See CONVECTIVE SIGMET.) (See CWA.) (See GRAPHICAL AIRMEN'S
METEOROLOGICAL INFORMATION.) (See ICAO term SIGMET INFORMATION.) (See
SAW.) (Refer to AIM.)
SIGMET INFORMATION [ICAO]
Information issued by a meteorological watch office concerning the occurrence or expected occurrence of
specified en-route weather phenomena which may affect the safety of aircraft operations.
A point, whether a named intersection, a NAVAID, a fix derived from a NAVAID(s), or geographical coordinate
expressed in degrees of latitude and longitude, which is established for the purpose of providing
separation, as a reporting point, or to delineate a route of flight.
SIMPLIFIED DIRECTIONAL FACILITY
A NAVAID used for nonprecision instrument approaches. The final approach course is similar to that of an ILS
localizer except that the SDF course may be offset from the runway, generally not more than 3 degrees, and
the course may be wider than the localizer, resulting in a lower degree of accuracy. (Refer to
AIM.)
SIMULATED FLAMEOUT
A practice approach by a jet aircraft (normally military) at idle thrust to a runway. The approach may start
at a runway (high key) and may continue on a relatively high and wide downwind leg with a continuous turn to
final. It terminates in landing or low approach. The purpose of this approach is to simulate a flameout. (See FLAMEOUT.)
SIMULTANEOUS CLOSE PARALLEL APPROACHES
A simultaneous, independent approach operation permitting ILS/RNAV/GLS approaches to airports having
parallel runways separated by at least 3,000 feet and less than 4300 feet between centerlines. Aircraft are
permitted to pass each other during these simultaneous operations. Integral parts of a total system are
radar, NTZ monitoring with enhanced FMA color displays that include aural and visual alerts and predictive
aircraft position software, communications override, ATC procedures, an Attention All Users Page (AAUP), PRM
in the approach name, and appropriate ground based and airborne equipment. High update rate surveillance
sensor required for certain runway or approach course separations.
SIMULTANEOUS (CONVERGING) DEPENDENT APPROACHES
An approach operation permitting ILS/RNAV/GLS approaches to runways or missed approach courses that
intersect where required minimum spacing between the aircraft on each final approach course is required.
SIMULTANEOUS (CONVERGING) INDEPENDENT APPROACHES
An approach operation permitting ILS/RNAV/GLS approaches to non-parallel runways where approach procedure
design maintains the required aircraft spacing throughout the approach and missed approach and hence the
operations may be conducted independently.
SIMULTANEOUS ILS APPROACHES
An approach system permitting simultaneous ILS approaches to airports having parallel runways separated by
at least 4,300 feet between centerlines. Integral parts of a total system are ILS, radar, communications,
ATC procedures, and appropriate airborne equipment. (See PARALLEL RUNWAYS.)
(Refer to
AIM.)
SIMULTANEOUS OFFSET INSTRUMENT APPROACH (SOIA)
An instrument landing system comprised of an ILS PRM, RNAV PRM or GLS PRM approach to one runway and an
offset LDA PRM with glideslope or an RNAV PRM or GLS PRM approach utilizing vertical guidance to another
where parallel runway spaced less than 3,000 feet and at least 750 feet apart. The approach courses converge
by 2.5 to 3 degrees. Simultaneous close parallel PRM approach procedures apply up to the point where the
approach course separation becomes 3,000 feet, at the offset MAP. From the offset MAP to the runway
threshold, visual separation by the aircraft conducting the offset approach is utilized. (Refer to
AIM.)
SIMULTANEOUS (PARALLEL) DEPENDENT APPROACHES
An approach operation permitting ILS/RNAV/GLS approaches to adjacent parallel runways where prescribed
diagonal spacing must be maintained. Aircraft are not permitted to pass each other during simultaneous
dependent operations. Integral parts of a total system ATC procedures, and appropriate airborne and ground
based equipment.
SINGLE DIRECTION ROUTES
Preferred IFR Routes which are sometimes depicted on high altitude en route charts and which are normally
flown in one direction only. (See PREFERRED IFR ROUTES.) (Refer to CHART
SUPPLEMENT U.S.)
SINGLE FREQUENCY APPROACH
A service provided under a letter of agreement to military single-piloted turbojet aircraft which permits
use of a single UHF frequency during approach for landing. Pilots will not normally be required to change
frequency from the beginning of the approach to touchdown except that pilots conducting an en route descent
are required to change frequency when control is transferred from the air route traffic control center to
the terminal facility. The abbreviation "SFA" in the DOD FLIP IFR Supplement under "Communications"
indicates this service is available at an aerodrome.
SINGLE-PILOTED AIRCRAFT
A military turbojet aircraft possessing one set of flight controls, tandem cockpits, or two sets of flight
controls but operated by one pilot is considered single-piloted by ATC when determining the appropriate air
traffic service to be applied. (See SINGLE FREQUENCY APPROACH.)
SKYSPOTTER
A pilot who has received specialized training in observing and reporting inflight weather phenomena.
SLASH
A radar beacon reply displayed as an elongated target.
A constellation of satellites that receives ADS-B Out broadcasts and relays that information to the
appropriate surveil- lance facility. The currently deployed SBA system is only capable of receiving
broadcasts from 1090ES- equipped aircraft, and not from those equipped with only a universal access
transceiver (UAT). Also, aircraft with a top-of-fuselage-mounted transponder antenna (required for TCAS II
installations) will be better received by SBA, especially at latitudes below 45 degrees. (See
AUTOMATIC DEPENDENT SURVEILLANCE-BROADCAST.) (See
AUTOMATIC DEPENDENT SURVEILLANCE-BROADCAST OUT.)
SPACE LAUNCH AND REENTRY AREA
Locations where commercial space launch and/or reentry operations occur. For pilot awareness, a
rocket-shaped symbol is used to depict space launch and reentry area on sectional aeronautical charts.
SPEAK SLOWER
Used in verbal communications as a request to reduce speech rate.
SPECIAL GOVERNMENT INTEREST (SGI)
A near real-time airspace authorization for Part 91 or Part 107 UAS, which supports activities that answer
significant and urgent governmental interests. These include: national defense, homeland security, law
enforcement, and emergency operations objectives.
SPECIAL ACTIVITY AIRSPACE (SAA)
Airspace with defined dimensions within the National Airspace System wherein limitations may be imposed upon
operations for national defense, homeland security, public interest, or public safety. Special activity
airspace includes but is not limited to the following; Air Traffic Control Assigned Airspace (ATCAA), Altitude
Reservations (ALTRV), Military Training Routes (MTR), Air Refueling Tracks and Anchors, Temporary Flight
Restrictions (TFR), Special Security Instructions (SSI), etc. Special Use Airspace (SUA) is a subset of
Special Activity Airspace. (See SPECIAL USE AIRSPACE.)
SPECIAL AIR TRAFFIC RULES (SATR)
Rules that govern procedures for conducting flights in certain areas listed in 14 CFR Part 93. The term
"SATR" is used in the United States to describe the rules for operations in specific areas designated in the
Code of Federal Regulations. (Refer to
14 CFR Part 93.)
SPECIAL EMERGENCY
A condition of air piracy or other hostile act by a person(s) aboard an aircraft which threatens the safety
of the aircraft or its passengers.
SPECIAL FLIGHT RULES AREA (SFRA)
An area in the NAS, described in 14 CFR Part 93, wherein the flight of aircraft is subject to special
traffic rules, unless otherwise authorized by air traffic control. Not all areas listed in 14 CFR Part 93
are designated SFRA, but special air traffic rules apply to all areas described in 14 CFR Part 93.
Airspace of defined dimensions identified by an area on the surface of the earth wherein activities must be
confined because of their nature and/or wherein limitations may be imposed upon aircraft operations that are
not a part of those activities. Types of special use airspace are:
Alert Area: Airspace which may contain a high volume of pilot training activities or an unusual
type of aerial activity, neither of which is hazardous to aircraft. Alert Areas are depicted on
aeronautical charts for the information of nonparticipating pilots. All activities within an Alert Area
are conducted in accordance with Federal Aviation Regulations, and pilots of participating aircraft as
well as pilots transiting the area are equally responsible for collision avoidance.
Controlled Firing Area: Airspace wherein activities are conducted under conditions so
controlled as to eliminate hazards to nonparticipating aircraft and to ensure the safety of persons and
property on the ground.
Military Operations Area (MOA): Permanent and temporary MOAs are airspace established outside
of Class A airspace area to separate or segregate certain nonhazardous military activities from IFR
traffic and to identify for VFR traffic where these activities are conducted. Permanent MOAs are
depicted on Sectional Aeronautical, VFR Terminal Area, and applicable En Route Low Altitude Charts.
National Security Area (NSA) Airspace of defined vertical and lateral dimensions established at
locations where there is a requirement for increased security of ground facilities. Pilots are requested
to voluntarily avoid flying through the depicted NSA. When a greater level of security is required, flight
through an NSA may be temporarily prohibited by establishing a TFR under the provisions of 14 CFR Section
99.7. Such prohibitions will be issued by FAA Headquarters and disseminated via the U.S. NOTAM System.
(Refer to AIM.)
Prohibited Area: Airspace designated under
14 CFR Part 73 within which no person may
operate an aircraft without the permission of the using agency. (Refer to
AIM.) (Refer to En Route Charts.)
Restricted Area: Permanent and temporary restricted areas are airspace designated under
14 CFR Part 73, within which the flight of
aircraft, while not wholly prohibited, is subject to restriction. Most restricted areas are designated
joint use and IFR/VFR operations in the area may be authorized by the controlling ATC facility when it
is not being utilized by the using agency. Permanent restricted areas are depicted on Sectional
Aeronautical, VFR Terminal Area, and applicable En Route charts. Where joint use is authorized, the name
of the ATC controlling facility is also shown.
Warning Area: A warning area is airspace of defined dimensions extending from 3 nautical miles
outward from the coast of the United States, that contains activity that may be hazardous to
nonparticipating aircraft. The purpose of such warning area is to warn nonparticipating pilots of the
potential danger. A warning area may be located over domestic or international waters or both.
SPECIAL VFR CONDITIONS
Meteorological conditions that are less than those required for basic VFR flight in Class B, C, D, or E
surface areas and in which some aircraft are permitted flight under visual flight rules. (See SPECIAL VFR OPERATIONS.) (Refer to 14 CFR Part 91.)
SPECIAL VFR FLIGHT [ICAO]
A VFR flight cleared by air traffic control to operate within Class B, C, D, and E surface areas in
meteorological conditions below VMC.
SPECIAL VFR OPERATIONS
Aircraft operating in accordance with clearances within Class B, C, D, and E surface areas in weather
conditions less than the basic VFR weather minima. Such operations must be requested by the pilot and
approved by ATC. (See SPECIAL VFR CONDITIONS.) (See ICAO term
SPECIAL VFR FLIGHT.)
An ATC procedure used to request pilots to adjust aircraft speed to a specific value for the purpose of
providing desired spacing. Pilots are expected to maintain a speed of plus or minus 10 knots or 0.02 Mach
number of the specified speed. Examples of speed adjustments are:
"Increase/reduce speed to Mach point (number.)"
"Increase/reduce speed to (speed in knots)" or "Increase/reduce speed (number of knots) knots."
SPEED BRAKES
Movable aerodynamic devices on aircraft that reduce airspeed during descent and landing.
SPEED SEGMENTS
Portions of the arrival route between the transition point and the vertex along the optimum flight path for
which speeds and altitudes are specified. There is one set of arrival speed segments adapted from each
transition point to each vertex. Each set may contain up to six segments.
SPEED ADVISORY
Speed advisories that are generated within Time-Based Flow Management to assist controllers to meet the
Scheduled Time of Arrival (STA) at the meter fix/meter arc. See also Ground-Based Interval
Management-Spacing (GIM-S) Speed Advisory.
SPOOFING
Denotes emissions of GNSS-like signals that may be acquired and tracked in combination with or instead of
the intended signals by civil receivers. The onset of spoofing effects can be instantaneous or delayed, and
effects can persist after the spoofing has ended. Spoofing can result in false and potentially confusing, or
hazardously misleading, position, navigation, and/or date/time information in addition to loss of GNSS use.
SQUAWK (Mode, Code, Function)
Used by ATC to instruct a pilot to activate the aircraft transponder and ADS-B Out with altitude reporting
enabled, or (military) to activate only specific modes, codes, or functions. Examples: "Squawk five seven
zero seven;" "Squawk three/alpha, two one zero five." (See TRANSPONDER.)
The placement, integration, and segregation of departure aircraft in designated movement areas of an airport
by departure fix, EDCT, and/or restriction.
STAND BY
Means the controller or pilot must pause for a few seconds, usually to attend to other duties of a higher
priority. Also means to wait as in "stand by for clearance." The caller should reestablish contact if a
delay is lengthy. "Stand by" is not an approval or denial.
A preplanned instrument flight rule (IFR) air traffic control (ATC) departure procedure printed for
pilot/controller use in graphic form to provide obstacle clearance and a transition from the terminal area
to the appropriate en route structure. SIDs are primarily designed for system enhancement to expedite
traffic flow and to reduce pilot/controller workload. ATC clearance must always be received prior to flying
a SID. (See IFR TAKEOFF MINIMUMS AND DEPARTURE
PROCEDURES.) (See OBSTACLE DEPARTURE PROCEDURE.) (Refer to
AIM.)
STANDARD RATE TURN
A turn of three degrees per second.
STANDARD TERMINAL ARRIVAL (STAR)
A preplanned instrument flight rule (IFR) air traffic control arrival procedure published for pilot use in
graphic and/or textual form. STARs provide transition from the en route structure to an outer fix or an
instrument approach fix/arrival waypoint in the terminal area.
Aircraft used in military, customs and police service, in the exclusive service of any government, or of any
political subdivision, thereof including the government of any state, territory, or possession of the United
States or the District of Columbia, but not including any government-owned aircraft engaged in carrying
persons or property for commercial purposes.
STATIC RESTRICTIONS
Those restrictions that are usually not subject to change, fixed, in place, and/or published.
STATIONARY AIRSPACE RESERVATION
The term used in oceanic ATC for airspace that encompasses activities in a fixed volume of airspace to be
occupied for a specified time period. Stationary Airspace Reservations may include activities such as special
tests of weapons systems or equipment; certain U.S. Navy carrier, fleet, and anti-submarine operations;
rocket, missile, and drone operations; and certain aerial refueling or similar operations.
(See STATIONARY ALTITUDE RESERVATION.)
An altitude reservation which encompasses activities in a fixed volume of airspace to be occupied for a
specified time period. Stationary ALTRVs may include activities such as special tests of weapons systems or
equipment;
certain U.S. Navy carrier, fleet, and anti-submarine operations; rocket, missile, and drone operations; and
certain aerial refueling or similar
operations.
STEP TAXI
To taxi a float plane at full power or high RPM.
STEP TURN
A maneuver used to put a float plane in a planing configuration prior to entering an active sea lane for
takeoff. The STEP TURN maneuver should only be used upon pilot request.
STEPDOWN FIX
A fix permitting additional descent within a segment of an instrument approach procedure by identifying a
point at which a controlling obstacle has been safely overflown.
STEREO ROUTE
A routinely used route of flight established by users and ARTCCs identified by a coded name; e.g., ALPHA 2.
These routes minimize flight plan handling and communications.
Used by ATC to instruct a pilot to turn off the automatic altitude reporting feature of the aircraft
transponder and ADS-B Out. It is issued when a verbally reported altitude varies by 300 feet or more from
the automatic altitude report. (See ALTITUDE READOUT.) (See TRANSPONDER.)
STOP AND GO
A procedure wherein an aircraft will land, make a complete stop on the runway, and then commence a takeoff
from that point. (See LOW APPROACH.) (See OPTION
APPROACH.)
Used by ATC to instruct a pilot to stop transponder and ADS-B transmissions, or to turn off only specified
functions of the aircraft transponder (military). (See STOP ALTITUDE
SQUAWK.) (See TRANSPONDER.)
STOP STREAM
Used by ATC to request a pilot to suspend electronic attack activity. (See JAMMING.)
STOPOVER FLIGHT PLAN
A flight plan format which permits in a single submission the filing of a sequence of flight plans through
interim full-stop destinations to a final destination.
STOPWAY
An area beyond the takeoff runway no less wide than the runway and centered upon the extended centerline of
the runway, able to support the airplane during an aborted takeoff, without causing structural damage to the
airplane, and designated by the airport authorities for use in decelerating the airplane during an aborted
takeoff.
STRAIGHT-IN APPROACH IFR
An instrument approach wherein final approach is begun without first having executed a procedure turn, not
necessarily completed with a straight-in landing or made to straight-in landing minimums. (See LANDING MINIMUMS.) (See STRAIGHT-IN
APPROACH VFR.) (See STRAIGHT-IN LANDING.)
STRAIGHT-IN APPROACH VFR
Entry into the traffic pattern by interception of the extended runway centerline (final approach course)
without executing any other portion of the traffic pattern. (See TRAFFIC
PATTERN.)
STRAIGHT-IN LANDING
A landing made on a runway aligned within 30° of the final approach course following completion of an
instrument approach. (See STRAIGHT-IN APPROACH IFR.)
A route assigned to pilots when any part of an airway or route is unusable because of NAVAID status. These
routes consist of:
Substitute routes which are shown on U.S. Government charts.
Routes defined by ATC as specific NAVAID radials or courses.
Routes defined by ATC as direct to or between NAVAIDs.
SUNSET AND SUNRISE
The mean solar times of sunset and sunrise as published in the Nautical Almanac, converted to local standard
time for the locality concerned. Within Alaska, the end of evening civil twilight and the beginning of
morning civil twilight, as defined for each locality.
SUPPLEMENTAL WEATHER SERVICE LOCATION
Airport facilities staffed with contract personnel who take weather observations and provide current local
weather to pilots via telephone or radio. (All other services are provided by the parent FSS.)
SUPPS
Refers to ICAO Document 7030 Regional Supplementary Procedures. SUPPS contain procedures for each ICAO
Region which are unique to that Region and are not covered in the worldwide provisions identified in the
ICAO Air Navigation Plan. Procedures contained in Chapter 8 are based in part on those published in SUPPS.
SURFACE AREA
The airspace contained by the lateral boundary of the Class B, C, D, or E airspace designated for an airport
that begins at the surface and extends upward.
SURFACE METERING PROGRAM
A capability within Terminal Flight Data Manager that provides the user with the ability to tactically
manage surface traffic flows through adjusting desired minimum and maximum departure queue lengths to
balance surface demand with capacity. When a demand/capacity imbalance for a surface resource is predicted,
a metering procedure is recommended.
SURFACE VIEWER
A capability within the Traffic Flow Management System that provides situational awareness for a
user-selected airport. The Surface Viewer displays a top-down view of an airport depicting runways,
taxiways, gate areas, ramps, and buildings. The display also includes icons representing aircraft and
vehicles currently on the surface, with identifying information. In addition, the display includes current
airport configuration information such as departure/arrival runways and airport departure/arrival rates.
SURPIC
A description of surface vessels in the area of a Search and Rescue incident including their predicted
positions and their characteristics. (Refer to FAA Order JO 7110.65, Para 1064, INFLIGHT CONTINGENCIES.)
SURVEILLANCE APPROACH
An instrument approach wherein the air traffic controller issues instructions, for pilot compliance, based
on aircraft position in relation to the final approach course (azimuth), and the distance (range) from the
end of the runway as displayed on the controller's radar scope. The controller will provide recommended
altitudes on final approach if requested by the pilot. (Refer to
AIM.)
SUSPICIOUS UAS
Suspicious UAS operations may include operating without authorization, loitering in the vicinity of
sensitive locations, (e.g., national security, law enforcement facilites, and critical infrastructure), or
disrupting normal air traffic operations resulting in runway changes, ground stops, pilot evasive action,
etc. The report of a UAS operation alone does not constitute suspicious activity. Development of a
comprehensive list of susppicious activities is not possible due to the vast number of situations that could
be considered suspicious. ATC must exercise sound judgment when identifying situations that could
consititute or indicate a suspicious activity.
Military activity accomplished by navigating along a preplanned route using internal aircraft systems to
maintain a desired track. This activity normally requires a lateral route width of 10 NM and altitude range
of 1,000 feet to 6,000 feet AGL with some route segments that permit terrain following.
An aircraft, normally military, possessing TACAN with DME but no VOR navigational system capability.
Clearances must specify TACAN or VORTAC fixes and approaches.
TACTICAL AIR NAVIGATION (TACAN)
An ultra-high frequency electronic rho-theta air navigation aid which provides suitably equipped aircraft a
continuous indication of bearing and distance to the TACAN station. (See VORTAC.)
(Refer to
AIM.)
TAILWIND
Any wind more than 90 degrees to the longitudinal axis of the runway. The magnetic direction of the runway
shall be used as the basis for determining the longitudinal axis.
The takeoff run available plus the length of any remaining runway or clearway beyond the far end of the
takeoff run available. (See ICAO term TAKEOFF DISTANCE AVAILABLE.)
[ICAO] The length of the takeoff run available plus the length of the clearway, if provided.
TAKEOFF HOLD LIGHTS (THL)
The THL system is composed of in-pavement lighting in a double, longitudinal row of lights aligned either
side of the runway centerline. The lights are focused toward the arrival end of the runway at the "line up
and wait" point, and they extend for 1,500 feet in front of the holding aircraft. Illuminated red lights
indicate to an aircraft in position for takeoff or rolling that it is unsafe to takeoff because the runway
is occupied or about to be occupied by an aircraft or vehicle.
TAKEOFF ROLL
The process whereby an aircraft is aligned with the runway centerline and the aircraft is moving with the
intent to take off. For helicopters, this pertains to the act of becoming airborne after departing a takeoff
area.
TAKEOFF RUN AVAILABLE (TORA)
The runway length declared available and suitable for the ground run of an airplane taking off. (See ICAO
term TAKEOFF RUN AVAILABLE.)
[ICAO] The length of runway declared available and suitable for the ground run of an aeroplane take-off.
A TFR is a regulatory action issued by the FAA via the U.S. NOTAM System, under the authority of United
States Code, Title 49. TFRs are issued within the sovereign airspace of the United States and its
territories to restrict certain aircraft from operating within a defined area on a temporary basis to
protect persons or property in the air or on the ground. While not all inclusive, TFRs may be issued for
disaster or hazard situations such as: toxic gas leaks or spills, fumes from flammable agents, aircraft
accident/incident sites, aviation or ground resources engaged in wildfire suppression, or aircraft relief
activities following a disaster. TFRs may also be issued in support of VIP movements; for reasons of
national security; or when determined necessary for the management of air traffic in the vicinity of aerial
demonstrations or major sporting events. NAS users or other interested parties should contact a FSS for TFR
information. Additionally, TFR information can be found in automated briefings, NOTAM publications, and on
the internet at http://www.faa.gov. The FAA also
distributes TFR information to aviation user groups for further dissemination.
TERMINAL AREA
A general term used to describe airspace in which approach control service or airport traffic control
service is provided.
TERMINAL AREA FACILITY
A facility providing air traffic control service for arriving and departing IFR, VFR, Special VFR, and on
occasion en route aircraft. (See APPROACH CONTROL FACILITY.) (See TOWER.)
TERMINAL AUTOMATION SYSTEMS (TAS)
TAS is used to identify the numerous automated tracking systems including STARS, and MEARTS.
TERMINAL DATA LINK SYSTEM (TDLS)
A system that provides Digital Automatic Terminal Information Service (DATIS) both on a specified radio
frequency and also, for subscribers, in a text message via data link to the cockpit or to a gate printer.
TDLS also provides Predeparture Clearances (PDC), at selected airports, to subscribers, through a service
provider, in text to the cockpit or to a gate printer. In addition, TDLS will emulate the Flight Data
Input/Output (FDIO) information within the control tower.
TERMINAL FLIGHT DATA MANAGER (TFDM)
An integrated tower flight data automation system to provide improved airport surface and terminal airspace
management. TFDM enhances traffic flow management data integration with Time-Based Flow Management (TBFM)
and Traffic Flow Management System (TFMS) to enable airlines, controllers, and airports to share and
exchange real-time data. This improves surface traffic management and enhances capabilities of TFMS and
TBFM. TFDM assists the Tower personnel with surface Traffic Flow Management (TFM) and Collaborative Decision
Making (CDM) and enables a fundamental change in the Towers from a local airport-specific operation to a
NAS-connected metering operation. The single platform consolidates multiple Tower automation systems,
including: Departure Spacing Program (DSP), Airport Resource Management Tool (ARMT), Electronic Flight Strip
Transfer System (EFSTS) and Surface Movement Advisor (SMA). TFDM data, integrated with other FAA systems
such as TBFM and TFMS, allows airlines, controllers, and airports to manage the flow of aircraft more
efficiently through all phases of flight from departure to arrival gate.
TERMINAL RADAR SERVICE AREA
Airspace surrounding designated airports wherein ATC provides radar vectoring, sequencing, and separation on
a full-time basis for all IFR and participating VFR aircraft. The AIM contains an explanation of TRSA. TRSAs
are depicted on VFR aeronautical charts. Pilot participation is urged but is not mandatory.
TERMINAL SEQUENCING AND SPACING (TSAS)
Extends scheduling and metering capabilities into the terminal area and provides metering automation tools
to terminal controllers and terminal traffic management personnel. Those controllers and traffic management
personnel become active participants in time-based metering operations as they work to deliver aircraft
accurately to Constraint Satisfaction Points within terminal airspace to include the runway in accordance
with scheduled times at those points. Terminal controllers are better able to utilize efficient flight
paths, such as Standard Instrument Approach Procedures (SIAPs) that require a Navigational Specification
(NavSpec) of RNP APCH with Radius-to-Fix (RF) legs, or Advanced RNP (A-RNP),through tools that support the
merging of mixed-equipage traffic flows. For example, merging aircraft flying RNP APCH AR with RF, A-RNP,
and non-RNP approach proce-dures. Additional fields in the flight plan will identify those flights capable
of flying the RNP APCH with RF or A-RNP procedures, and those flights will be scheduled for those types of
procedures when available. TSAS will schedule these and the non-RNP aircraft to a common merge point.
Terminal traffic management personnel have improved situation awareness using displays that allow for the
monitoring of terminal metering operations, similar to the displays used today by center traffic management
personnel to monitor en route metering operations.
TERMINAL VFR RADAR SERVICE
A national program instituted to extend the terminal radar services provided instrument flight rules (IFR)
aircraft to visual flight rules (VFR) aircraft. The program is divided into four types service referred to
as basic radar service, terminal radar service area (TRSA) service, Class B service and Class C service. The
type of service provided at a particular location is contained in the Chart Supplement U.S.
Basic Radar Service: These services are provided for VFR aircraft by all commissioned terminal
radar facilities. Basic radar service includes safety alerts, traffic advisories, limited radar
vectoring when requested by the pilot, and sequencing at locations where procedures have been
established for this purpose and/or when covered by a letter of agreement. The purpose of this service
is to adjust the flow of arriving IFR and VFR aircraft into the traffic pattern in a safe and orderly
manner and to provide traffic advisories to departing VFR aircraft.
TRSA Service: This service provides, in addition to basic radar service, sequencing of all IFR
and participating VFR aircraft to the primary airport and separation between all participating VFR
aircraft. The purpose of this service is to provide separation between all participating VFR aircraft
and all IFR aircraft operating within the area defined as a TRSA.
Class C Service: This service provides, in addition to basic radar service, approved separation
between IFR and VFR aircraft, and sequencing of VFR aircraft, and sequencing of VFR arrivals to the
primary airport.
Class B Service: This service provides, in addition to basic radar service, approved separation
of aircraft based on IFR, VFR, and/or weight, and sequencing of VFR arrivals to the primary airport(s).
TERMINAL-VERY HIGH FREQUENCY OMNIDIRECTIONAL RANGE STATION
A very high frequency terminal omnirange station located on or near an airport and used as an approach aid.
(See NAVIGATIONAL AID.) (See VOR.)
TERRAIN AWARENESS WARNING SYSTEM (TAWS)
An onboard, terrain proximity alerting system providing the aircrew 'Low Altitude warnings' to allow
immediate pilot action.
TERRAIN FOLLOWING
The flight of a military aircraft maintaining a constant AGL altitude above the terrain or the highest
obstruction. The altitude of the aircraft will constantly change with the varying terrain and/or
obstruction.
TETRAHEDRON
A device normally located on uncontrolled airports and used as a landing direction indicator. The small end
of a tetrahedron points in the direction of landing. At controlled airports, the tetrahedron, if installed,
should be disregarded because tower instructions supersede the indicator. (See
SEGMENTED CIRCLE.) (Refer to
AIM.)
The electronically administered free test required for all recreational UAS operators referred to as the
aeronautical knowledge and safety test, under 49 USC §44809 (g).
THREE-HOUR TARMAC RULE
Rule that relates to Department of Transportation (DOT) requirements placed on airlines when tarmac delays
are anticipated to reach 3 hours.
The theoretical height above the runway threshold at which the aircraft's glideslope antenna would be if the
aircraft maintains the trajectory established by the mean ILS glideslope or the altitude at which the
calculated glidepath of an RNAV or GPS approaches. (See GLIDESLOPE.) (See THRESHOLD.)
The FSS primarily responsible for providing FSS services, including telecommunications services for landing
facilities or navigational aids located within the boundaries of a flight plan area (FPA). Three-letter
identifiers are assigned to each FSS/FPA and are annotated as tie-in facilities in the Chart Supplement
U.S., the Alaska Supplement, the Pacific Supplement, and FAA Order JO 7350.8, Location Identifiers. Large
consolidated FSS facilities may have many tie-in facilities or FSS sectors within one facility. (See FLIGHT PLAN AREA.) (See FLIGHT SERVICE
STATION.)
TIME-BASED FLOW MANAGEMENT (TBFM)
A foundational Decision Support Tool for time-based management in the en route and terminal environments.
TBFM's core function is the ability to schedule aircraft within a stream of traffic to reach a defined
constraint point (e.g., meter fix/meter arc) at specified times, creating a time-ordered sequence of
traffic. The scheduled times allow for merging of traffic flows, efficiently utilizing airport and airspace
capacity while minimizing coordination and reducing the need for vectoring/holding. The TBFM schedule is
calculated using current aircraft estimated time of arrival at key defined constraint points based on wind
forecasts, aircraft flight plan, the desired separation at the constraint point and other parameters. The
schedule applies spacing only when needed to maintain the desired separation at one or more constraint
points. This includes, but is not limited to, Single Center Metering (SCM), Adjacent Center Metering (ACM),
En Route Departure Capability (EDC), Integrated Departure/Arrival Capability (IDAC), Ground-based Interval
Management-S pacing (GIM-S), Departure Scheduling, and Extended/Coupled Metering.
TIME-BASED MANAGEMENT (TBM)
A methodology for managing the flow of air traffic through the assignment of time at specific points for an
aircraft. TBM applies time to manage and condition air traffic flows to mitigate demand/capacity imbalances
and enhance efficiency and predictability of the NAS. Where implemented, TBM tools will be used to manage
traffic even during periods when demand does not exceed capacity. This will sustain operational
predictability and assure the regional/national strategic plan is maintained. TBM uses capabilities within
TFMS, TBFM, and TFDM. These programs are designed to achieve a specified interval between aircraft.
Different types of programs accommodate different phases of flight.
TIME GROUP
Four digits representing the hour and minutes from the Coordinated Universal Time (UTC) clock. FAA uses UTC
for all operations. The term "ZULU" may be used to denote UTC. The word "local" or the time zone equivalent
shall be used to denote local when local time is given during radio and telephone communications. When
written, a time zone designator is used to indicate local time; e.g. "0205M" (Mountain). The local time may
be based on the 24-hour clock system. The day begins at 0000 and ends at 2359.
TIMELINE GRAPHICAL USER INTERFACE (TGUI)
A TBFM display that uses timelines to display the Estimated Time of Arrival and Scheduled Time of Arrival of
each aircraft to specified constraint points. The TGUI can also display the pre-departure and scheduled
aircraft.
The burning of fuel at the end of an exhaust pipe or stack of a reciprocating aircraft engine, the result of
an excessive richness in the fuel air mixture.
For IFR flights, the estimated time required from take-off to arrive over that designated point, defined by
reference to navigation aids, from which it is intended that an instrument approach procedure will be
commenced, or, if no navigation aid is associated with the destination aerodrome, to arrive over the
destination aerodrome. For VFR flights, the estimated time required from take-off to arrive over the
destination aerodrome. (See ICAO term ESTIMATED ELAPSED TIME.)
TOUCH-AND-GO
An operation by an aircraft that lands and departs on a runway without stopping or exiting the runway.
The first 3,000 feet of the runway beginning at the threshold. The area is used for determination of
Touchdown Zone Elevation in the development of straight-in landing minimums for instrument approaches.
[ICAO] The portion of a runway, beyond the threshold, where it is intended landing aircraft first contact
the runway.
TOUCHDOWN ZONE ELEVATION
The highest elevation in the first 3,000 feet of the landing surface. TDZE is indicated on the instrument
approach procedure chart when straight-in landing minimums are authorized. (See
TOUCHDOWN ZONE.)
A terminal facility that uses air/ground communications, visual signaling, and other devices to provide ATC
services to aircraft operating in the vicinity of an airport or on the movement area. Authorizes aircraft to
land or takeoff at the airport controlled by the tower or to transit the Class D airspace area regardless of
flight plan or weather conditions (IFR or VFR). A tower may also provide approach control services (radar or
nonradar). (See AIRPORT TRAFFIC CONTROL SERVICE.) (See APPROACH CONTROL FACILITY.) (See APPROACH CONTROL SERVICE.) (See MOVEMENT
AREA.) (See TOWER EN ROUTE CONTROL SERVICE.) (See ICAO
term
AERODROME CONTROL TOWER.) (Refer to
AIM.)
TOWER EN ROUTE CONTROL SERVICE
The control of IFR en route traffic within delegated airspace between two or more adjacent approach control
facilities. This service is designed to expedite traffic and reduce control and pilot communication
requirements.
The facility station pressure instrument, with certification/calibration traceable to the National Institute
of Standards and Technology. Traceable pressure standards may be mercurial barometers, commissioned
ASOS/AWSS or dual transducer AWOS, or portable pressure standards or DASI.
TRACK
The actual flight path of an aircraft over the surface of the earth. (See COURSE.) (See FLIGHT PATH.) (See ROUTE.) (See ICAO term TRACK.)
[ICAO] The projection on the earth's surface of the path of an aircraft, the direction of which path at any
point is usually expressed in degrees from North (True, Magnetic, or Grid).
TRACK OF INTEREST (TOI)
Displayed data representing an airborne object that threatens or has the potential to threaten North America
or National Security. Indicators may include, but are not limited to: noncompliance with air traffic control
instructions or aviation regulations; extended loss of communications; unusual transmissions or unusual
flight behavior; unauthorized intrusion into controlled airspace or an ADIZ; noncompliance with issued
flight restrictions/security procedures; or unlawful interference with airborne flight crews, up to and
including hijack. In certain circumstances, an object may become a TOI based on specific and credible
intelligence pertaining to that particular aircraft/ object, its passengers, or its cargo.
TRACK OF INTEREST RESOLUTION
A TOI will normally be considered resolved when: the aircraft/object is no longer airborne; the aircraft
complies with air traffic control instructions, aviation regulations, and/or issued flight
restrictions/security procedures; radio contact is reestablished and authorized control of the aircraft is
verified; the aircraft is intercepted and intent is verified to be nonthreatening/nonhostile; TOI was
identified based on specific and credible intelligence that was later determined to be invalid or
unreliable; or displayed data is identified and characterized as invalid.
TRAFFIC
A term used by a controller to transfer radar identification of an aircraft to another controller for
the purpose of coordinating separation action. Traffic is normally issued:
In response to a handoff or point out,
In anticipation of a handoff or point out, or
In conjunction with a request for control of an aircraft.
A term used by ATC to refer to one or more aircraft.
TRAFFIC ADVISORIES
Advisories issued to alert pilots to other known or observed air traffic which may be in such proximity to
the position or intended route of flight of their aircraft to warrant their attention. Such advisories may
be based on:
Visual observation.
Observation of radar identified and nonidentified aircraft targets on an ATC radar display, or
Verbal reports from pilots or other facilities.
Note 1: The word "traffic" followed by additional information, if known, is used to provide such
advisories; e.g., "Traffic, 2 o'clock, one zero miles, southbound, eight thousand."
Note 2: Traffic advisory service will be provided to the extent possible depending on higher priority
duties of the controller or other limitations; e.g., radar limitations, volume of traffic, frequency
congestion, or controller workload. Radar/ nonradar traffic advisories do not relieve the pilot of
his/her responsibility to see and avoid other aircraft. Pilots are cautioned that there are many times
when the controller is not able to give traffic advisories concerning all traffic in the aircraft's
proximity; in other words, when a pilot requests or is receiving traffic advisories, he/she should not
assume that all traffic will be issued.
(aircraft call sign), TURN (left/right) IMMEDIATELY, (climb/descend) AND MAINTAIN (altitude). (See SAFETY ALERT.)
TRAFFIC ALERT AND COLLISION AVOIDANCE SYSTEM
An airborne collision avoidance system based on radar beacon signals which operates independent of
ground-based equipment. TCAS-I generates traffic advisories only. TCAS-II generates traffic advisories, and
resolution (collision avoidance) advisories in the vertical plane.
The broadcast of ATC derived traffic information to ADSB equipped (1090ES or UAT) aircraft. The source of
this traffic information is derived from ground based air traffic surveillance sensors, typically from radar
targets. TISB service will be available throughout the NAS where there are both adequate surveillance
coverage (radar) and adequate broadcast coverage from ADSB ground stations. Loss of TISB will occur when an
aircraft enters an area not covered by the GBT network. If this occurs in an area with adequate surveillance
coverage (radar), nearby aircraft that remain within the adequate broadcast coverage (ADSB) area will view
the first aircraft. TISB may continue when an aircraft enters an area with inadequate surveillance coverage
(radar); nearby aircraft that remain within the adequate broadcast coverage (ADSB) area will not view the
first aircraft.
Tools used to manage demand with capacity in the National Airspace System (NAS.) TMIs can be used to manage
NAS resources (e.g., airports, sectors, airspace) or to increase the efficiency of the operation. TMIs can
be either tactical (i.e., short term) or strategic (i.e., long term), depending on the type of TMI and the
operational need.
TRAFFIC MANAGEMENT PROGRAM ALERT
A term used in a Notice to Air Missions (NOTAM) issued in conjunction with a special traffic management
program to alert pilots to the existence of the program and to refer them to a special traffic management
program advisory message for program details. The contraction TMPA is used in NOTAM text.
TRAFFIC MANAGEMENT UNIT
The entity in ARTCCs and designated terminals directly involved in the active management of facility
traffic. Usually under the direct supervision of an assistant manager for traffic management.
TRAFFIC NO FACTOR
Indicates that the traffic described in a previously issued traffic advisory is no factor.
TRAFFIC NO LONGER OBSERVED
Indicates that the traffic described in a previously issued traffic advisory is no longer depicted on radar,
but may still be a factor.
TRAFFIC PATTERN
The traffic flow that is prescribed for aircraft landing at, taxiing on, or taking off from an airport. The
components of a typical traffic pattern are upwind leg, crosswind leg, downwind leg, base leg, and final
approach.
Upwind Leg: A flight path parallel to the landing runway in the direction of landing.
Crosswind Leg: A flight path at right angles to the landing runway off its upwind end.
Downwind Leg: A flight path parallel to the landing runway in the direction opposite to
landing. The downwind leg normally extends between the crosswind leg and the base leg.
Base Leg: A flight path at right angles to the landing runway off its approach end. The base
leg normally extends from the downwind leg to the intersection of the extended runway centerline.
Final Approach: A flight path in the direction of landing along the extended runway centerline.
The final approach normally extends from the base leg to the runway. An aircraft making a straight-in
approach VFR is also considered to be on final approach.
TSD is a computer system that receives radar track data from all 20 CONUS ARTCCs, organizes this data into a
mosaic display, and presents it on a computer screen. The display allows the traffic management coordinator
multiple methods of selection and highlighting of individual aircraft or groups of aircraft. The user has
the option of superimposing these aircraft positions over any number of background displays. These
background options include ARTCC boundaries, any stratum of en route sector boundaries, fixes, airways,
military and other special use airspace, airports, and geopolitical boundaries. By using the TSD, a
coordinator can monitor any number of traffic situations or the entire system wide traffic flows.
TRAJECTORY
A EDST representation of the path an aircraft is predicted to fly based upon a Current Plan or Trial Plan.
(See EN ROUTE DECISION SUPPORT TOOL.)
TRAJECTORY-BASED OPERATIONS (TBO)
An Air Traffic Management method for strategically planning and managing flights throughout the operation by
using Time-Based Management (TBM), information exchange between air and ground systems, and the aircraft's
ability to fly trajectories in time and space. Aircraft trajectory is defined in four dimensions - latitude,
longitude, altitude, and time.
TRAJECTORY MODELING
The automated process of calculating a trajectory.
TRAJECTORY OPTIONS SET (TOS)
A TOS is an electronic message, submitted by the operator, that is used by the Collaborative Trajectory
Options Program (CTOP) to manage the airspace captured in the traffic management program. The TOS will allow
the operator to express the route and delay trade-off options that they are willing to accept.
TRANSFER OF CONTROL
That action whereby the responsibility for the separation of an aircraft is transferred from one controller
to another.
[ICAO] Transfer of responsibility for providing air traffic control service.
TRANSFERRING CONTROLLER
A controller/facility transferring control of an aircraft to another controller/facility. (See ICAO term
TRANSFERRING UNIT/CONTROLLER.)
Air traffic control unit/air traffic controller in the process of transferring the responsibility for
providing air traffic control service to an aircraft to the next air traffic control unit/air traffic
controller along the route of flight.
Note: See definition of accepting unit/controller.
TRANSITION
The general term that describes the change from one phase of flight or flight condition to another; e.g.,
transition from en route flight to the approach or transition from instrument flight to visual flight.
TRANSITION POINT
A point at an adapted number of miles from the vertex at which an arrival aircraft would normally commence
descent from its en route altitude. This is the first fix adapted on the arrival speed segments.
TRANSITIONAL AIRSPACE
That portion of controlled airspace wherein aircraft change from one phase of flight or flight condition to
another.
An apparatus used to determine visibility by measuring the transmission of light through the atmosphere. It
is the measurement source for determining runway visual range (RVR). (See
VISIBILITY.)
TRANSMITTING IN THE BLIND
A transmission from one station to other stations in circumstances where two-way communication cannot be
established, but where it is believed that the called stations may be able to receive the transmission.
TRANSPONDER
The airborne radar beacon receiver/transmitter portion of the Air Traffic Control Radar Beacon System
(ATCRBS) which automatically receives radio signals from interrogators on the ground, and selectively
replies with a specific reply pulse or pulse group only to those interrogations being received on the mode
to which it is set to respond. (See INTERROGATOR.) (Refer to
AIM.)
[ICAO] A receiver/transmitter which will generate a reply signal upon proper interrogation; the
interrogation and reply being on different frequencies.
Phraseology used to inform a VFR pilot the aircraft's assigned beacon code and position have been observed.
Specifically, this term conveys to a VFR pilot the transponder reply has been observed and its position
correlated for transit through the designated area.
TRIAL PLAN
A proposed amendment which utilizes automation to analyze and display potential conflicts along the
predicted trajectory of the selected aircraft.
An aircraft having a jet engine in which the energy of the jet operates a turbine which in turn operates the
air compressor.
TURBOPROP AIRCRAFT
An aircraft having a jet engine in which the energy of the jet operates a turbine which drives the
propeller.
An atmospheric phenomenon that causes changes in aircraft altitude, attitude, and or airspeed with aircraft
reaction depending on intensity. Pilots report turbulence intensity according to aircraft's reaction as
follows:
Light: Causes slight, erratic changes in altitude and or attitude (pitch, roll, or yaw).
Moderate: Similar to Light but of greater intensity. Changes in altitude and or attitude occur
but the aircraft remains in positive control at all times. It usually causes variations in indicated
airspeed.
Severe: Causes large, abrupt changes in altitude and or attitude. It usually causes large
variations in indicated airspeed. Aircraft may be momentarily out of control.
Extreme: The aircraft is violently tossed about and is practically impossible to control. It
may cause structural damage.
Defined grid squares showing maximum altitudes around airports where the FAA may authorize Part 107 sUAS
operations without additional safety analysis. The maps should be consulted prior to conducting UAS operations
(Part 91, Part 107 or Section 44809) in controlled airspace. The UASFM will aid in determining if the airspace
authorization or waivers are necessary. UASFM(s) are charted on the UAS Data Delivery System (UDDS) at the
following website address: https://faa.maps.arcgis.com/apps/webappviewer/index.html?id=9c2e4406710048e19806ebf6a06754ad
UAS TEST SITE
Independently owned UAS test & research sites, recognized by the FAA.
UAS TRAFFIC MANAGEMENT (UTM)
The unmanned aircraft traffic management ecosystem that will allow multiple low altitude BVLOS operations
and which is separate from, but complementary to, FAA's Air Traffic Control System.
The frequency band between 300 and 3,000 MHz. The bank of radio frequencies used for military air/ground
voice communications. In some instances this may go as low as 225 MHz and still be referred to as UHF.
ULTRALIGHT VEHICLE
A single-occupant aeronautical vehicle operated for sport or recreational purposes which does not require
FAA registration, an airworthiness certificate, nor pilot certification. Operation of an ultralight vehicle
in certain airspace requires authorization from ATC (Refer to
14 CFR Part 103.)
UNABLE
Indicates inability to comply with a specific instruction, request, or clearance.
UNASSOCIATED
A radar target that does not display a data block with flight identification and altitude information. (See ASSOCIATED.)
UNCONTROLLED AIRSPACE
Airspace in which aircraft are not subject to controlled airspace (Class A, B, C, D, or E) separation
criteria.
UNDER THE HOOD
Indicates that the pilot is using a hood to restrict visibility outside the cockpit while simulating
instrument flight. An appropriately rated pilot is required in the other control seat while this operation
is being conducted. (Refer to 14 CFR Part 91.)
UNFROZEN
The Scheduled Time of Arrival (STA) tags, which are still being rescheduled by the time based flow
management (TBFM) calculations. The aircraft will remain unfrozen until the time the corresponding estimated
time of arrival (ETA) tag passes the preset freeze horizon for that aircraft's stream class. At this point
the automatic rescheduling will stop, and the STA becomes "frozen."
UNICOM
A non-government communication facility which may provide airport information at certain airports. Locations
and frequencies of UNICOMs are shown on aeronautical charts and publications. (See CHART SUPPLEMENT U.S.) (Refer to
AIM.)
UNMANNED AIRCRAFT (UA)
A device used or intended to be used for flight that has no onboard pilot. This device can be any type of
airplane, helicopter, airship, or powered-lift aircraft. Unmanned free balloons, moored balloons, tethered
aircraft, gliders, and unmanned rockets are not considered to be a UA.
UNMANNED AIRCRAFT SYSTEM (UAS)
An unmanned aircraft and its associated elements related to safe operations, which may include control
stations (ground, ship, or air based), control links, support equipment, payloads, flight termination
systems, and launch/recovery equipment. It consists of three elements: unmanned aircraft, control station,
and data link.
UNPUBLISHED ROUTE
A route for which no minimum altitude is published or charted for pilot use. It may include a direct route
between NAVAIDs, a radial, a radar vector, or a final approach course beyond the segments of an instrument
approach procedure. (See PUBLISHED ROUTE.) (See ROUTE.)
UNRELIABLE (GPS/WAAS)
An advisory to pilots indicating the expected level of service of the GPS and/or WAAS may not be available.
Pilots must then determine the adequacy of the signal for desired use.
A subset of Advanced Air Mobility (AAM), referring to an air transportation system utilizing highly
automated aircraft to transport passengers or cargo in urban/suburban areas.
URGENCY
A condition of being concerned about safety and of requiring timely but not immediate assistance; a
potential distress condition.
[ICAO] A condition concerning the safety of an aircraft or other vehicle, or of person on board or in sight,
but which does not require immediate assistance.
A heading issued to an aircraft to provide navigational guidance by radar. (See ICAO term
RADAR VECTORING.)
VERIFY
Request confirmation of information; e.g., "verify assigned altitude."
VERIFY SPECIFIC DIRECTION OF TAKEOFF (OR TURNS AFTER TAKEOFF)
Used by ATC to ascertain an aircraft's direction of takeoff and/or direction of turn after takeoff. It is
normally used for IFR departures from an airport not having a control tower. When direct communication with
the pilot is not possible, the request and information may be relayed through an FSS, dispatcher, or by
other means. (See IFR TAKEOFF MINIMUMS AND DEPARTURE
PROCEDURES.)
VERTICAL NAVIGATION (VNAV)
A function of area navigation (RNAV) equipment which calculates, displays, and provides vertical guidance to
a profile or path.
VERTICAL SEPARATION
Separation between aircraft expressed in units of vertical distance. (See
SEPARATION.)
VERTICAL TAKEOFF AND LANDING AIRCRAFT
Aircraft capable of vertical climbs and/or descents and of using very short runways or small areas for
takeoff and landings. These aircraft include, but are not limited to, helicopters. (See SHORT TAKEOFF AND LANDING AIRCRAFT.)
VERY HIGH FREQUENCY
The frequency band between 30 and 300 MHz. Portions of this band, 108 to 118 MHz, are used for certain
NAVAIDs; 118 to 136 MHz are used for civil air/ground voice communications. Other frequencies in this band
are used for purposes not related to air traffic control.
An aircraft conducting flight in accordance with visual flight rules. (See
VISUAL FLIGHT RULES.)
VFR CONDITIONS
Weather conditions equal to or better than the minimum for flight under visual flight rules. The term may be
used as an ATC clearance/instruction only when:
An IFR aircraft requests a climb/descent in VFR conditions.
The clearance will result in noise abatement benefits where part of the IFR departure route does not
conform to an FAA approved noise abatement route or altitude.
A pilot has requested a practice instrument approach and is not on an IFR flight plan.
Note: All pilots receiving this authorization must comply with the VFR visibility and distance from cloud
criteria in 14 CFR Part 91. Use of the term
does not relieve controllers of their responsibility to separate aircraft in Class B and Class C airspace
or TRSAs as required by FAA Order JO 7110.65. When used as an ATC clearance/instruction, the term may be
abbreviated "VFR;" e.g., "MAINTAIN VFR," "CLIMB/DESCEND VFR," etc.
Routes used by the Department of Defense and associated Reserve and Air Guard units for the purpose of
conducting low-altitude navigation and tactical training under VFR below 10,000 feet MSL at airspeeds in
excess of 250 knots IAS.
VFR NOT RECOMMENDED
An advisory provided by a flight service station to a pilot during a preflight or inflight weather briefing
that flight under visual flight rules is not recommended. To be given when the current and/or forecast
weather conditions are at or below VFR minimums. It does not abrogate the pilot's authority to make his/her
own decision.
VFR-ON-TOP
ATC authorization for an IFR aircraft to operate in VFR conditions at any appropriate VFR altitude (as
specified in 14 CFR and as restricted by ATC). A pilot receiving this authorization must comply with the VFR
visibility, distance from cloud criteria, and the minimum IFR altitudes specified in
14 CFR Part 91. The use of this term does not
relieve controllers of their responsibility to separate aircraft in Class B and Class C airspace or TRSAs as
required by FAA Order JO 7110.65.
An electronically displayed map on the radar display that may depict data such as airports, heliports,
runway centerline extensions, hospital emergency landing areas, NAVAIDs and fixes, reporting points,
airway/route centerlines, boundaries, handoff points, special use tracks, obstructions, prominent geographic
features, map alignment indicators, range accuracy marks, minimum vectoring altitudes.
VISIBILITY
The ability, as determined by atmospheric conditions and expressed in units of distance, to see and identify
prominent unlighted objects by day and prominent lighted objects by night. Visibility is reported as statute
miles, hundreds of feet or meters. (Refer to
14 CFR Part 91.) (Refer to
AIM.)
Flight Visibility: The average forward horizontal distance, from the cockpit of an aircraft in
flight, at which prominent unlighted objects may be seen and identified by day and prominent lighted
objects may be seen and identified by night.
Ground Visibility: Prevailing horizontal visibility near the earth's surface as reported by the
United States National Weather Service or an accredited observer.
Prevailing Visibility: The greatest horizontal visibility equaled or exceeded throughout at
least half the horizon circle which need not necessarily be continuous.
Runway Visual Range (RVR): An instrumentally derived value, based on standard calibrations,
that represents the horizontal distance a pilot will see down the runway from the approach end. It is
based on the sighting of either high intensity runway lights or on the visual contrast of other targets
whichever yields the greater visual range. RVR, in contrast to prevailing or runway visibility, is based
on what a pilot in a moving aircraft should see looking down the runway. RVR is horizontal visual range,
not slant visual range. It is based on the measurement of a transmissometer made near the touchdown
point of the instrument runway and is reported in hundreds of feet. RVR, where available, is used in
lieu of prevailing visibility in determining minimums for a particular runway.
Touchdown RVR: The RVR visibility readout values obtained from RVR equipment serving the
runway touchdown zone.
Mid-RVR: The RVR readout values obtained from RVR equipment located midfield of the runway.
Rollout RVR: The RVR readout values obtained from RVR equipment located nearest the rollout
end of the runway.
[ICAO] The ability, as determined by atmospheric conditions and expressed in units of distance, to see and
identify prominent unlighted objects by day and prominent lighted objects by night.
Flight Visibility: The visibility forward from the cockpit of an aircraft in flight.
Ground Visibility: The visibility at an aerodrome as reported by an accredited observer.
Runway Visual Range [RVR]: The range over which the pilot of an aircraft on the centerline of a
runway can see the runway surface markings or the lights delineating the runway or identifying its
centerline.
VISUAL APPROACH
An approach conducted on an instrument flight rules (IFR) flight plan which authorizes the pilot to proceed
visually and clear of clouds to the airport. The pilot must, at all times, have either the airport or the
preceding aircraft in sight. This approach must be authorized and under the control of the appropriate air
traffic control facility. Reported weather at the airport must be ceiling at or above 1,000 feet and
visibility of 3 miles or greater.
[ICAO] An approach by an IFR flight when either part or all of an instrument approach procedure is not
completed and the approach is executed in visual reference to terrain.
A departure option for an IFR aircraft, operating in visual meteorological conditions equal to or greater
than the specified visibility and ceiling, to visually conduct climbing turns over the airport to the
published "climb to" altitude from which to proceed with the instrument portion of the departure. VCOA
procedures are developed to avoid obstacles greater than 3 statute miles from the departure end of the
runway as an alternative to complying with climb gradients greater than 200 feet per nautical mile. Pilots
are responsible to advise ATC as early as possible of the intent to fly the VCOA option prior to departure.
These textual procedures are published in the 'Take Off Minimums and (Obstacle) Departure Procedures'
section of the Terminal Procedures Publications and/or appear as an option on a Graphic ODP. (See AIM.)
VISUAL DESCENT POINT
A defined point on the final approach course of a nonprecision straight-in approach procedure from which
normal descent from the MDA to the runway touchdown point may be commenced, provided the approach threshold
of that runway, or approach lights, or other markings identifiable with the approach end of that runway are
clearly visible to the pilot.
A person who is designated by the remote pilot in command to assist the remote pilot in command and the
person operating the flight controls of the small UAS (sUAS) to see and avoid other air traffic or objects
aloft or on the ground.
A means employed by ATC to separate aircraft in terminal areas and en route airspace in the NAS. There are
two ways to effect this separation:
The tower controller sees the aircraft involved and issues instructions, as necessary, to ensure that
the aircraft avoid each other.
A pilot sees the other aircraft involved and upon instructions from the controller provides his/her own
separation by maneuvering his/her aircraft as necessary to avoid it. This may involve following another
aircraft or keeping it in sight until it is no longer a factor.
The VSCS is a computer controlled switching system that provides air traffic controllers with all voice
circuits (air to ground and ground to ground) necessary for air traffic control. (Refer to
AIM.)
VOR
A ground-based electronic navigation aid transmitting very high frequency navigation signals, 360 degrees in
azimuth, oriented from magnetic north. Used as the basis for navigation in the National Airspace System. The
VOR periodically identifies itself by Morse Code and may have an additional voice identification feature.
Voice features may be used by ATC or FSS for transmitting instructions/information to pilots. (See NAVIGATIONAL AID.) (Refer to
AIM.)
Circular patterns of air created by the movement of an airfoil through the air when generating lift. As an
airfoil moves through the atmosphere in sustained flight, an area of area of low pressure is created above
it. The air flowing from the high pressure area to the low pressure area around and about the tips of the
airfoil tends to roll up into two rapidly rotating vortices, cylindrical in shape. These vortices are the
most predominant parts of aircraft wake turbulence and their rotational force is dependent upon the wing
loading, gross weight, and speed of the generating aircraft. The vortices from medium to super aircraft can
be of extremely high velocity and hazardous to smaller aircraft. (See AIRCRAFT
CLASSES.) (See WAKE TURBULENCE.) (Refer to
AIM.)
VOT
A ground facility which emits a test signal to check VOR receiver accuracy. Some VOTs are available to the
user while airborne, and others are limited to ground use only. (See CHART
SUPPLEMENT U.S.) (Refer to 14 CFR Part
91.) (Refer to
AIM.)
A set of optimized wake separation standards, featuring an increased number of aircraft wake categories, in
use at select airports, which allows reduced wake intervals. (See
WAKE TURBULENCE.)
WAKE TURBULENCE
Phenomena resulting from the passage of an aircraft through the atmosphere. The term includes vortices,
thrust stream turbulence, jet blast, jet wash, propeller wash, and rotor wash both on the ground and in the
air. (See AIRCRAFT CLASSES.) (See JET BLAST.) (See VORTICES.) (Refer to
AIM.)
A predetermined geographical position used for route/instrument approach definition, progress reports,
published VFR routes, visual reporting points or points for transitioning and/or circumnavigating controlled
and/or special use airspace, that is defined relative to a VORTAC station or in terms of latitude/longitude
coordinates.
WEATHER ADVISORY
In aviation weather forecast practice, an expression of hazardous weather conditions not predicted in the
Aviation Surface Forecast, Aviation Cloud Forecast, or area forecast, as they affect the operation of air
traffic and as prepared by the NWS. (See AIRMET.)
(See GRAPHICAL AIRMEN'S METEOROLOGICAL
INFORMATION.)
(See SIGMET.)
WEATHER RECONNAISSANCE AREA (WRA)
A WRS is airspace with defined dimensions and published by Notice to Air Missions, which is established to
support weather reconnaissance/research flights. Air traffic control services are not provided within WRAs.
Only participating weather reconnaissance/ research aircraft from the 53rd Weather Reconnaissance Squadron
and National Oceanic and Atmospheric Administration Aircraft Operations Center are permitted to operate
within a WRA. A WRA may only be established in airspace within U.S. Flight Information Regions outside of
U.S. territorial airspace.
WHEN ABLE
In conjunction with ATC instructions, gives the pilot the latitude to delay compliance until a condition
or event has been reconciled. Unlike "pilot discretion," when instructions are prefaced "when able," the
pilot is expected to seek the first opportunity to comply.
In conjunction with a weather deviation clearance, requires the pilot to determine when he/she is clear
of weather, then execute ATC instructions.
Once a maneuver has been initiated, the pilot is expected to continue until the specifications of the
instructions have been met. "When able," should not be used when expeditious compliance is required.
WIDE-AREA AUGMENTATION SYSTEM (WAAS)
The WAAS is a satellite navigation system consisting of the equipment and software which augments the GPS
Standard Positioning Service (SPS). The WAAS provides enhanced integrity, accuracy, availability, and
continuity over and above GPS SPS. The differential correction function provides improved accuracy required
for precision approach.
WIDE AREA MULTILATERATION (WAM)
A distributed surveillance technology which may utilize any combination of signals from Air Traffic Control
Radar Beacon System (ATCRBS) (Modes A and C) and Mode S transponders, and ADS-B transmissions. Multiple
geographically dispersed ground sensors measure the time-of-arrival of the transponder messages. Aircraft
position is determined by joint processing of the time-difference-of-arrival (TDOA) measurements computed
between a reference and the ground stations' measured time-of-arrival.
WILCO
I have received your message, understand it, and will comply with it.
WIND GRID DISPLAY
A display that presents the latest forecasted wind data overlaid on a map of the ARTCC area. Wind data is
automatically entered and updated periodically by transmissions from the National Weather Service. Winds at
specific altitudes, along with temperatures and air pressure can be viewed.
WIND SHEAR
A change in wind speed and/or wind direction in a short distance resulting in a tearing or shearing effect.
It can exist in a horizontal or vertical direction and occasionally in both.
WIND SHEAR ESCAPE
An unplanned abortive maneuver initiated by the pilot in command (PIC) as a result of onboard cockpit
systems. Wind shear escapes are characterized by maximum thrust climbs in the low altitude terminal
environment until wind shear conditions are no longer detected.
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