[Ref. Pilot’s Handbook of Aeronautical Knowledge, FAA-H-8083-25B Page 7-34,7-35]
WHY airplanes need to be pressurized?
Aircraft are flown at high altitudes for various reasons. However, the air at high altitudes is thin, and oxygen levels very low, so aircraft have been pressurized to protect occupants against hypoxia.
The reason is not only because of passenger comfort, but also the fact that if the cabin altitude is maintained at 8,000 feet or below, the use of oxygen equipment is not required.
In addition, the pressurization system permits a reasonably fast exchange of air from the inside to the outside of the cabin. This is necessary to eliminate odors and to remove stale air.
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