IFR Arr/Dep to intesecting runways

[Juliet Victor]

Places with intersecting runways when you have an arrival to one and a departure from the other both ifr when would be the latest you would launch the departure? I've heard of a couple of places making the controllers apply 3 miles between the arrival and the intersection. That doesn't seem right and I can't find that.

 

[Termine]

Even if you somehow could use two-increasing-to-three it would become moot

Well. Careful now.

The complete rule is that you can let the aircraft get closer than three miles, airborne, so long as:

1. At the time the departure begins takeoff roll, the arrival is no closer than two miles, AND
2. Separation will increase to three miles within one minute of departure.

If #2 will never be satisfied (say you're launching a C172 in front of a SWA arrival) then that's not a legal application of the rule. So even if the rule becomes moot later on when you have some other form of separation, you still lost separation for the time when you were trying to use 2-to-3-in-1.

But in any case I've come to the same conclusion: the rule can't be applied to intersecting runways.

 

[AB19]

Well. Careful now.

The complete rule is that you can let the aircraft get closer than three miles, airborne, so long as:

1. At the time the departure begins takeoff roll, the arrival is no closer than two miles, AND
2. Separation will increase to three miles within one minute of departure.

If #2 will never be satisfied (say you're launching a C172 in front of a SWA arrival) then that's not a legal application of the rule. So even if the rule becomes moot later on when you have some other form of separation, you still lost separation for the time when you were trying to use 2-to-3-in-1.

But in any case I've come to the same conclusion: the rule can't be applied to intersecting runways.

Why do you think the rule can’t be applied? What separation are you saying you need in that circumstance?

 

[Termine]

Why do you think the rule can’t be applied?

Basically what rhombus said: It really doesn't seem (to my reading) like 5-8-4 applies to intersection runways. In fact I'm not 100% certain it applies to closer-than-2500-feet parallels either, but I can see the argument there. This is based on the wording in the note, which references "the runway."

But say I'm wrong—say the note is just worded poorly, and actually you are able to use the rule with intersecting runways. In order to do it properly, aircraft speeds and performance have to permit an increase to three miles' worth of airborne separation "within 1 minute after takeoff." Frustratingly they don't specify whether that means the moment the aircraft begins takeoff roll or the moment that it rotates, and even more frustratingly the .65 is not very consistent:

• 3-9-6e says that radar-based WT sep has to exist when the #2 aircraft becomes airborne.
• 3-9-6e Note 2 (which really applies to 3-9-6f/g/h) says that the timer starts when the #1 aircraft begins takeoff roll.
• 3-9-7a uses the wording "has taken off" and I was taught (at the academy and in the field) that that means rotation.
• Pilot-controller glossary defines the term "takeoff roll" but doesn't define "takeoff."
• Pilot-controller glossary defines "cleared for takeoff" as ATC authorization for an aircraft to depart. Nothing we didn't know already, not very useful.

But on the balance I would say the "within 1 minute after takeoff" timer has to start when the departure begins rolling—that's how runway separation works in all other cases except intersection-departure-WT. And if the intersection is anywhere except the very beginning of the runway that means you're using up a lot of your one minute with the departure moving towards the arrival instead of away from it... although you are helped by the departure moving at cross paths to the arrival once it does finally pass the intersection, which increases the separation faster than if it was departing straight-out the same runway (thanks, Pythagoras).

(Again, to be very clear, as soon as the departure crosses the intersection you now have diverging separation—the departure has crossed the projected flight path of the arrival. But that doesn't matter when you're trying to apply 5-8-4 prior to the intersection. If they're not going to be three miles apart within 1 minute, you had a deal; just because you later re-gained approved separation doesn't mean the deal didn't happen.)

But... maybe I'm wrong about all that. Maybe the one-minute timer starts when the departure rotates and you'll end up having the three miles so you can properly apply 5-8-4. Or maybe your airport layout is such that the intersection is only 500' downfield from where the departure starts their roll, so the "airborne before the intersection" situation doesn't come up; 3-10-4 plus 5-5-7 is all you need. I can be persuaded, perhaps.

What separation are you saying you need in that circumstance?

Between the time the departure rotates and the time the arrival crosses the intersection, you need three miles of airborne separation between the two aircraft. So you have to launch the departure in time for them to cross the intersection when the arrival is no closer than three miles from that intersection.

 

[AB19]

Basically what rhombus said: It really doesn't seem (to my reading) like 5-8-4 applies to intersection runways. In fact I'm not 100% certain it applies to closer-than-2500-feet parallels either, but I can see the argument there. This is based on the wording in the note, which references "the runway."

But say I'm wrong—say the note is just worded poorly, and actually you are able to use the rule with intersecting runways. In order to do it properly, aircraft speeds and performance have to permit an increase to three miles' worth of airborne separation "within 1 minute after takeoff." Frustratingly they don't specify whether that means the moment the aircraft begins takeoff roll or the moment that it rotates, and even more frustratingly the .65 is not very consistent:

• 3-9-6e says that radar-based WT sep has to exist when the #2 aircraft becomes airborne.
• 3-9-6e Note 2 (which really applies to 3-9-6f/g/h) says that the timer starts when the #1 aircraft begins takeoff roll.
• 3-9-7a uses the wording "has taken off" and I was taught (at the academy and in the field) that that means rotation.
• Pilot-controller glossary defines the term "takeoff roll" but doesn't define "takeoff."
• Pilot-controller glossary defines "cleared for takeoff" as ATC authorization for an aircraft to depart. Nothing we didn't know already, not very useful.

But on the balance I would say the "within 1 minute after takeoff" timer has to start when the departure begins rolling—that's how runway separation works in all other cases except intersection-departure-WT. And if the intersection is anywhere except the very beginning of the runway that means you're using up a lot of your one minute with the departure moving towards the arrival instead of away from it... although you are helped by the departure moving at cross paths to the arrival once it does finally pass the intersection, which increases the separation faster than if it was departing straight-out the same runway (thanks, Pythagoras).

(Again, to be very clear, as soon as the departure crosses the intersection you now have diverging separation—the departure has crossed the projected flight path of the arrival. But that doesn't matter when you're trying to apply 5-8-4 prior to the intersection. If they're not going to be three miles apart within 1 minute, you had a deal; just because you later re-gained approved separation doesn't mean the deal didn't happen.)

But... maybe I'm wrong about all that. Maybe the one-minute timer starts when the departure rotates and you'll end up having the three miles so you can properly apply 5-8-4. Or maybe your airport layout is such that the intersection is only 500' downfield from where the departure starts their roll, so the "airborne before the intersection" situation doesn't come up; 3-10-4 plus 5-5-7 is all you need. I can be persuaded, perhaps.


Between the time the departure rotates and the time the arrival crosses the intersection, you need three miles of airborne separation between the two aircraft. So you have to launch the departure in time for them to cross the intersection when the arrival is no closer than three miles from that intersection.

My facility had this situation brought up two years ago now, someone argued that you needed three at the intersection, others argued you only needed two. What we got told from outside the facility is that for someone taking off the intersecting runway, you only needed two miles through the intersection

 

[Termine]

two miles through the intersection

Okay then. I'm going to copy the rule in full here so we have the context:

TERMINAL. Except as provided in paragraph 5-8-5, Departures and Arrivals on Parallel or Nonintersecting Diverging Runways, separate a departing aircraft from an arriving aircraft on final approach by a minimum of 2 miles if separation will increase to a minimum of 3 miles (5 miles when 40 miles or more from the antenna) within 1 minute after takeoff.

NOTE-

1. This procedure permits a departing aircraft to be released so long as an arriving aircraft is no closer than 2  miles from the runway at the time. This separation is determined at the time the departing aircraft commences takeoff roll.
2. Consider the effect surface conditions, such as ice, snow, and other precipitation, may have on known aircraft performance characteristics, and the influence these conditions may have on the pilot's ability to commence takeoff roll in a timely manner.

So what they told you, essentially, is that the "minimum of 2 miles" wording from the rule itself is the important part, and not "from the runway" nor "separation is determined at the time the departing aircraft commences takeoff roll" from the Note? The minimum separation occurs when the departure is at the intersection, so that's when you need to have 2 miles. Well, that wasn't my first or second interpretation but if that's how they want you to apply it then there it is.

 

[AB19]

Okay then. I'm going to copy the rule in full here so we have the context:



So what they told you, essentially, is that the "minimum of 2 miles" wording from the rule itself is the important part, and not "from the runway" nor "separation is determined at the time the departing aircraft commences takeoff roll" from the Note? The minimum separation occurs when the departure is at the intersection, so that's when you need to have 2 miles. Well, that wasn't my first or second interpretation but if that's how they want you to apply it then there it is.

Sorry maybe I phrased it wrong, the arrival could not be closer than a two mile final before the departing aircraft was through the intersection was how they told us to apply the rule for intersecting runways. The arrival runway was 10 and departure was 34. Not sure if the headings of the runway played into their interpretation.

 

[A2J]

With the application of 5-5-7 diverging courses, it says "all other approved separation may be discontinued and passing and diverging separation applied when you observe the aircraft crossing the flight path of another by a minimum of 15 degrees for same/crossing courses."

So, with everything discussed prior, wouldn't basic diverging courses take place once you observe the target pass through the other arrivals flight path?

Also, every airfield is so different I can only assume everywhere applies it differently.