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B737 Pressurisation

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B737 Pressurisation

Old 5th Apr 2022, 12:00
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Join Date: Mar 2013
Location: 36,000'
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B737 Pressurisation

As per the FCOM
In certain circumstances the selected LAND ALT may exceed the target cabin altitude determined by the differential pressure limits. In these cases, the controller will maintain a cabin altitude slightly below the selected LAND ALT.
Any examples... Can some one please explain.

Last edited by B737NG_Pilot; 5th Apr 2022 at 12:24.
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Old 5th Apr 2022, 13:13
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Join Date: Jan 2008
Location: Denver
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Lacking additional context, I would think this has to do with the fact that there are an increasing number of medium-jet-capable commercial airports at elevations higher than what are usually considered "safe" cabin altitudes.

e.g. Daocheng Yading Intl, at 14000+ feet elevation.


If the system is designed to always maintain a max. cabin altitude of, say, 7500-10000 feet, that will be a issue. A minor one - the aircraft can be "depressurized" on landing - but not something designed into the normal limits of the sensors and gauges.

I believe that there are some aircraft with modified systems for such airports, but a "bog-standard" 737 or similar jet may need to go to one, and the FCOM item is just a reminder of the unusual situation.
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