This information bulletin is designed for cabin crew and will supplement your airline's cabin crew emergency procedures manual and should enhance your knowledge about what can occur during an aircraft depressurisation.
Why are aircraft pressurised?
Modern aircraft are designed to fly at high altitudes. For example, a Boeing 747 aircraft normally cruises at an altitude of 28,000 – 35,000 ft. This is because aircraft consume less fuel and fly in relatively smooth air, avoiding bad weather and turbulence. However, the human body is not designed to survive at such high altitudes so the air pressure inside the cabin must be controlled.
The air pressure inside the cabin cannot usually be kept the same as the ambient air pressure at ground level as doing so would put excessive stress on the aircraft fuselage. Therefore, the cabin air pressure altitude (as measured by the equivalent outside altitude) gradually rises from takeoff to a maximum of 8,000 ft during the cruise. During the descent to the destination airport, the cabin pressure altitude is gradually reduced to match the ambient air pressure of the airport. Without a fully functional pressurised cabin, passengers and crew need to use oxygen systems at the altitudes typically attained during cruise.
What is depressurisation?
Depressurisation, also called decompression, is the reduction of atmospheric pressure inside a contained space such as the cabin of a pressurised aircraft.