Cabin and airport pressure

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14 years 7 months

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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?

Original post
Profile picture for user DME

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15 years 6 months

Posts: 862

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

Profile picture for user Skymonster

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15 years 7 months

Posts: 1,953

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

Member for

14 years 7 months

Posts: 1,101


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 000ยด. There is Bangda in Tibet, though...
Profile picture for user Hugh Jarse

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15 years

Posts: 192

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.