Ceiling (aeronautics):
In aeronautics, a ceiling is the maximum density altitude an aircraft can reach under a set of conditions.
[edit] Service ceiling
The service ceiling attempts to capture the maximum usable altitude of an aircraft. Specifically, it is the density altitude at which flying in a clean configuration, at the best rate of climb airspeed for that altitude and with all engines operating and producing maximum continuous power, will produce a 100 feet per minute climb. Margin to stall at service ceiling is 1.5g.
The one engine inoperative (OEI) service ceiling of a twin-engine, fixed-wing aircraft is the density altitude at which flying in a clean configuration, at the best rate of climb airspeed for that altitude with one engine producing maximum continuous power and the other engine shut down and feathered, will produce a 50 feet per minute climb.
However some performance charts will define the service ceiling as the pressure altitude at which the aircraft will have the capability of climbing at 50 ft/min with one propeller feathered.
[edit] Absolute ceiling
A less often used term is the absolute ceiling – the highest altitude an airplane can sustain level flight, or altitude above which the cabin pressurization system can no longer maintain a sufficient oxygen level for passengers and crew, and where the pressure differential is so great as to put severe stress on the pressure cabin of the aircraft. Most commercial jetliners have a ceiling of about 42,000 feet (12,802 m) while some business jets can reach 52,000 feet or higher (15,850 meters.)
[edit] Combat ceiling
It is the highest altitude at which an aircraft is expected to have a 500 feet per minute climb
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