2-7-3

Altimeter Settings Greater Than 31.00 Inches Mercury

JO 7110.65BB, Change 3, effective July 9, 2026 · Official text on faa.gov

When the barometric pressure is greater than 31.00 inches mercury (31” Hg), issue the altimeter setting and phraseology that high barometric pressure procedures are in effect:

En Route/Arrivals. Advise pilots to leave altimeter set to 31.00 until reaching final approach fix.
Phraseology

ALTIMETER (setting) HIGH BAROMETRIC PRESSURE RESTRICTIONS IN EFFECT, SET THREE ONE ZERO ZERO UNTIL REACHING THE FINAL APPROACH FIX.
Departures. Advise pilots to set altimeter to 31.00 prior to reaching any mandatory/crossing altitude or 1,500 feet AGL, whichever is lower.
Phraseology

ALTIMETER (setting) HIGH BAROMETRIC PRESSURE RESTRICTIONS IN EFFECT, SET THREE ONE ZERO ZERO PRIOR TO REACHING (mandatory/crossing altitude or 1,500 feet AGL, whichever is lower).
Affected Air Route Traffic Control Centers (ARTCC) must request, via the U.S. NOTAM Office (USNOF), that a high barometric pressure NOTAM be issued for flying in regions where barometric pressure is above or forecast to be above 31” Hg.
Note
1. Altitude reporting transponders transmit the pressure altitude (Flight Level) of the aircraft. The altimeter setting does not directly affect the transponder reported altitude. ATC automation applies the current altimeter setting to the pressure altitude received and displays the altitude of the aircraft above mean sea level (MSL).
2. With a barometric pressure of 31.30” Hg and the aircraft's altimeter set at 31.00” Hg, the Mode C transponder will transmit the actual altitude of 3,300, feet while the altimeter only shows 3,000 feet. This will occur unless local directives authorize entering the altimeter setting 31.00” Hg into the ATC automation regardless of the actual barometric pressure.
3. Airports unable to accurately measure barometric pressures above 31.00” Hg. will report the barometric pressure as “missing” or “in excess of 31.00” Hg.” Flight operations to or from those airports are restricted to VFR weather conditions.