Aircrew members check their oxygen system equipment using the appropriate checklist or technical manual. The Army's fixed-wing aircraft can fly at higher altitudes than crew members can physiologically tolerate. Therefore, cabin pressurization was developed for the safety and comfort of crew members and passengers. The most efficient method for protecting crew members flying at altitude is to increase the barometric pressure inside the cabin area so that it is greater than the ambient pressure outside. In high-altitude flight without pressurization, crew members require continual use of oxygen equipment.
Continual use increases crew fatigue.
Pressurization, however, does have disadvantages. If crew members encounter problems with cabin pressurization, they may suffer serious physiological impairment. Because greater pressure must exist inside the cabin than outside, the aircraft wall must be structurally reinforced to contain this pressure. This reinforcement increases the design and maintenance costs of the aircraft, and the added weight and increased power requirements reduce its performance. Cabin pressurization is achieved by extracting outside ambient air, forcing it through compressors, cooling it, and maintaining it at a given cabin altitude.