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Old 19th April 2008 | 23:58
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Old Fella
 
Joined: Feb 2008
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From: Wingham NSW Australia
Cabin Altitude v's Aircraft Altitude

Normal practice in my experience has been to set planned cruise altitude plus 1000' on the pressurisation controller. This gives a buffer between the pressure differential you will hold and the max differential allowed. The rate of change in cabin altitude is normally set to give approximately 500'/min rate of change in the climb and, for pax comfort, a maximum of 300'/min on descent. If you are cruising at the lower level where the cabin will be maintained at sea level the rate of pressurisation will be such that the cabin remains at sea level (assuming your airfield of departure was at sea level). If you are climbing to the higher levels the rate of pressurisation will be such that the cabin altitude will climb steadily from whatever it was at your departure airfield to whatever it will be at your cruise level. On all the aircraft I crewed the cabin pressure controller rate could be changed if required, however most had a "normal" index at which the rate was set. Have not been in a L1011 since 1986, so the actual figures escape me.
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