B737NG_Pilot
5th Apr 2022, 12:00
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.
pattern_is_full
5th Apr 2022, 13:13
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.
https://www.airport-technology.com/features/feature-the-top-10-highest-altitude-airports-in-the-world/
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.