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4 Answers

Above 31.00 in Hg: Flight prohibited or different procedures?

Asked by: 8028 views , , , ,
Commercial Pilot, FAA Regulations, General Aviation

While studying for my commercial written, I came across a question regarding regulations when the pressure is 31.00 in Hg or greater.  The correct answer stated that flight was prohibited.  Through further research, I have found things saying that you just set all altimeter to 31.00 and leave it, when below 18,000 ft.  Any ideas what this regulation is?

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4 Answers

  1. Wesley Beard on Dec 30, 2010

    You are prohibited from flying where the barometric pressure is higher than 31.00″.
    § 91.144 Temporary restriction on flight operations during abnormally high barometric pressure conditions.
    (a) Special flight restrictions. When any information indicates that barometric pressure on the route of flight currently exceeds or will exceed 31 inches of mercury, no person may operate an aircraft or initiate a flight contrary to the requirements established by the Administrator and published in a Notice to Airmen issued under this section.
    (b) Waivers. The Administrator is authorized to waive any restriction issued under paragraph (a) of this section to permit emergency supply, transport, or medical services to be delivered to isolated communities, where the operation can be conducted with an acceptable level of safety.

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  2. Kent Shook on Dec 30, 2010

    I’ve never experienced it myself, but… This isn’t an outright prohibition. Notice that it says “contrary to the requirements established by… NOTAM.”
    As to what actually happens in this situation: Everyone uses 31.00 within the geographic area defined in the NOTAM. This can be found in FAA Order 7110.65T, the bible of Air Traffic Control. Here is the pertinent quote from that document, section 2-7-2(g):
    “g. When the barometric pressure is greater than 31.00 inches Hg., issue the altimeter setting and:
    1. En Route/Arrivals. Advise pilots to remain set on altimeter 31.00 until reaching final approach segment.
    2. Departures. Advise pilots to set altimeter 31.00 prior to reaching any mandatory/crossing altitude or 1,500 feet AGL, whichever is lower. PHRASEOLOGY- ALTIMETER, THREE ONE TWO FIVE, SET THREE ONE ZERO ZERO UNTIL REACHING THE FINAL APPROACH FIX.”

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  3. MaggotCFII on Jan 04, 2011

    Another source would be the “Aeronautical Information Manual”, A/K/A the “AIM”.
    Take a look at Chapter 7, Section 2.
    If you don’t have the actual book, it is available on the FAA.gov site.
    Good luck with the written!

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