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Altitude versus cabin altitude

Published on 07/09/2015 01:00 - By

This summer, we have received a number of reactions from you concerning one of our short instructional videos ("In your opinion") concerning the external altitude, which therefore requires the cabin of an aircraft to be pressurized, but many of you understood "cabin altitude". The nuance is subtle, yet the two terms are very different.

The cabin altitude is the maintained atmospheric pressure inside an aircraft cabin, corresponding to a certain altitude. Francis Carla, General Manager - Liebherr Aerospace Toulouse: "When it is cruising, a commercial aircraft flies at an altitude of 35,000 feet (10,700 metres), and cabin altitude is between 6,000 and 8,000 feet (1,800 to 2,400 metres). This corresponds to normal pressurization system functions, and to ensure better cabin comfort."

But why isn’t it possible to reduce the cabin altitude of a ‘plane to that near sea level? "If we have lower cabin altitudes, we have higher differential pressures between the aircraft and the cabin interior, therefore the aircraft structure, itself, would have to be able to resist these higher pressure differentials. ‘Planes would be too heavy and therefore unacceptable in terms of performance" explains Francis Carla.

For optimal flying conditions, cabin altitude ranges between 6,000 feet (1,800 metres) for new generation aircraft and 8,000 ft (2,400 metres) for older aircraft. As for the aircraft cabin, it is an absolute necessity that it be pressurized when the aircraft’s altitude exceeds 10,000 feet (3,000 metres) because above that, the air, therefore oxygen, is rarefied.

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