Ceiling (aeronautics)

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 if it has a propeller, the propeller is feathered), will produce a given rate of climb, usually 50 ft/min (0.25 m/s).

[2] 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 (0.25 m/s) with one propeller feathered.

The absolute ceiling is therefore the altitude at which the engines are operating at maximum thrust, yet can only generate enough lift to match the weight of the aircraft.

It is impossible to reach for most (because of the vertical speed asymptotically approaching zero) without afterburners or other devices temporarily increasing thrust.

Flight at the absolute ceiling is also not economically advantageous due to the low indicated airspeed which can be sustained: although the true airspeed at an altitude is typically greater than indicated airspeed (IAS), the difference is not enough to compensate for the fact that IAS at which minimum drag is achieved is usually low, so a flight at an absolute ceiling altitude results in a low TAS as well, and therefore in a high fuel burn rate per distance traveled.