Originally Posted by Mr Boeing
The Cabin Pressure Control System allows the flight crew to set the planned cruise flight altitude (FLT ALT) and the altitude of the intended landing field (LAND ALT). These altitudes are then used by the pressurization system to calculate a pressure schedule specific to the planned flight. The pressurization system is designed to maintain a comfortable and safe cabin altitude throughout the duration of the flight based on the FLT ALT and LAND ALT set during preflight. The only time a change in FLT ALT or LAND ALT is required in flight is when the final cruise or landing altitude is different than that selected during preflight