AIRCRAFT


PRESSURIZATION In order to provide a comfortable and safe environment inside the cabin, the aircraft is pressurized. This is accomplished by forcing outside air into the cabin, maintaining a constant pressure. The atmosphere inside the aircraft is set to an altitude lower than the actual flight level. This system is closely monitored and the flight deck is notified of any significant fluctuations.


The cabin pressure is generally set between 5,000 and 8,000 ft AMSL (Above mean sea level). This is dependent upon the type of aircraft and the altitude at which they are flying. Newer model aircraft offer lower and lower cabin altitudes, which is far more comfortable for the passengers.


Regulations call for Aircraft operating above 25,000 ft. MSL to provide a minimum 10-minute supply of


supplemental oxygen to the passengers. This is accomplished through the use of an automatically deployed oxygen mask at each passenger seat. The system will automatically deploy at 15,000 ft. of cabin altitude or less.


35,000 30,000 25,000 20,000 15,000 10,000 5,000


Outside Altitude (physical altitude of the aircraft)


Cabin Altitude (pressurized altitude of cabin)


Regulations governing operations at altitude:


FAR §91.211 Supplemental Oxygen, states that no person may operate a civil aircraft of U.S. registry with a pressurized cabin at flight altitudes above flight level 250 MSL unless at least a 10-minute supply of supplemental oxygen, in addition to


any requirement for crew/cockpit oxygen, is available for each occupant of the aircraft for use when a descent is necessary due to loss of cabin pressurization.


FAR §135.157 Oxygen equipment requirements, state that above 15,000 ft MSL, oxygen must be provided to each occupant of the aircraft, other than the pilots, for one hour unless,


at all times during flight above that altitude, the aircraft can descend to 15,000 ft MSL within four minutes, in which case only a 30-minute supply is required. Canadian CAR 604 and EASA requirements are similar to U.S. FAR requirements.


High Altitude Awareness Training 2


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