The requirements for cabin pressure for all types of aircraft have been established for the Armed Services in military specifications, by the Federal Aviation Authority and by the SAE in recommendations. These requirements limit the cabin altitude to 8000 ft in transport and long range military aircraft. In the fighter aircraft, when the pilot uses oxygen and the mission duration is relatively brief, cabin altitudes up to 25,000 ft are allowed. Supersonic transports, which operate at high speed and high altitude, have short flight durations and high rates of descent. To avoid an uncomfortable rate of change of cabin pressure when descending from high altitudes, a maximum cabin altitude of 6000 ft is recommended. The pressurization system design considerations presented in this AIR deal with human physiological requirements, characteristics of pressurization air sources, methods of controlling cabin pressure, cabin leakage control, leakage calculation methods, and methods of emergency cabin pressure release.