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  • chornedsnorkack
    Rank 5 Registered User
    • Jul 2005
    • 1108

    Cabin and airport pressure

    Normally the airplanes are supposed to keep cabin pressure at or below 8000 feet at all times. If it exceeds 10 000 feet, there is warning horn, and at 14 000 feet, masks in cabin drop out.

    What happens, however, if the originating or destination airport is located near or above 8000 feet?
  • DME
    DME
    Fly me to the Moon
    • Aug 2004
    • 914

    #2
    Same drill I think.

    On the deck, the A/C would sit as it sits at an airport with 2ft elevation, upon departure they would pressurise the hull to 8000ft and continue to climb to to cruise level.

    Wonder what the highest level airfield in the world is? Say it's 24,000 foot. What would they do to pressurise then??

    dme
    Loganair Islander from Papa Westry to Westry....Tower: Logan123 cleared for takeoff. Logan123: Cleared for takeoff Logan123. 38 seconds later....Logan123 finals for Westry!!!!!!

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    • Skymonster
      Rank 5 Registered User
      • Jul 2004
      • 1986

      #3
      Originally posted by chornedsnorkack
      What happens, however, if the originating or destination airport is located near or above 8000 feet?
      System has to be reset so that the cabin pressure decreases as the aeroplane decends. A case a few years ago where an AA 757 landed at La Paz, Bolivia (elevation 13000' or so), and the doors were opened (no problems as outside pressure was lower than inside). End result was that all the masks deployed, resulting in a two day delay whilst engineers came out to fix the system.

      Andy

      PS: La Paz El Alto at 13000' or so is one of the higest in the world (I think Lahsa in Tibet may be the only higher commercial airport). Its no problem really though - we flew in an unpressurized Curtiss C-46 to 16000' without any oxygen
      Last edited by Skymonster; 20th October 2005, 19:26.
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      • chornedsnorkack
        Rank 5 Registered User
        • Jul 2005
        • 1108

        #4
        Originally posted by Skymonster
        PS: La Paz El Alto at 13000' or so is one of the higest in the world (I think Lahsa in Tibet may be the only higher commercial airport).
        Actually, Lhasa is lower, below 12 000. There is Bangda in Tibet, though...

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        • Hugh Jarse
          Senior Member
          • Feb 2005
          • 193

          #5
          If landing at an airport that is close to 8000' the cabin just doesn't descend when the aircraft does. If the airport in question is above 8000' then different problems are encountered as mentioned above. This is part of the reason why most commercial aircraft have an airport elevation restriction that allows a maximum of 8400' or there abouts.

          No matter what, on landing the outflow valve drives fully open and equalises the pressure. Should this not work fully there are also overboard exhaust valves which look after both positive and negative pressure situation.

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