Re: 767 Service Ceiling

From: (Eric Hoffman)
Organization: Eurocontrol
Date:         11 Aug 94 13:30:14 
References:   1 2
Followups:    1
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In article <airliners.1994.1500@ohare.Chicago.COM>, (Morten Norby Larsen) writes:
> In article <airliners.1994.1490@ohare.Chicago.COM>,
> (Terrell D. Drinkard) writes:
> >Interestingly, service ceiling is a light aircraft type of parameter.  It
> >is fairly meaningless for heavy commercial airplanes.  The cruise altitude
> >is generally pretty close to optimum cruise altitude at any given stage of
> >the flight.  This is an economic issue as it is pretty costly to fly off
> >optimum.  The 500 fpm climb rate line is generally well above the optimum
> >cruise altitude, and service ceiling is defined as the altitude where the
> >rate of climb is 100 fpm.  The lowest climb parameter I've seen is 300 fpm,
> >and that is well above even the 500 fpm line.

The service ceiling is defined as the altitude where the climb rate drops
to 500fpm for Commercial/Jet and 100fpm for Commercial/Piston-propeller.

Note that usually the operational altitude limitation (as found in manuals) 
is computed with the cruise thrust rating. So you can definitely fly
above this altitude (selecting a climb or max continuous thrust rating),
but it will probably be at the expense of your engine life expectancy
(and BTW the time/distance required to climb there can even be found in
the summary climb performace tables from the AC perf manuals).

Related point: are you legally allowed to fly (or plan to fly) a 
commercial airliner above its service ceiling? I tend to believe that 
you are suppose to keep some maneuvrability margin in the vertical plane
(same stuff as more the 1.2 g margin). But that's a guess.


Eric Hoffman
EUROCONTROL Experimental Center
Center for Aircraft Performance and Operations