What is the absolute ceiling of the A319-100, B737-700 and A220? I have found the service ceiling in Jane's and their type certificate data sheets, but nothing on the absolute ceiling.
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2$\begingroup$ The absolute ceiling is a very dangerous place to be. $\endgroup$– John KJul 15, 2021 at 13:50
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1$\begingroup$ For a sufficiently light aircraft (since max altitude varies with weight & atmospheric conditions), it would be well above the max certified altitude. Which means you'd need test flight data -- nobody's going to publish stuff that assumes/encourages flying above the operating limitation of the max certified altitude. $\endgroup$– Ralph J ♦Jul 15, 2021 at 13:53
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$\begingroup$ @JohnK, why is an absolute ceiling a dangerous place? You just set full power, maintain Vy with pitch and keep climbing until it won't climb any more. Now coffin corner (which is what these aircraft are limited by in practice) is of course a different matter. $\endgroup$– Jan HudecJul 15, 2021 at 16:47
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2$\begingroup$ Because you are balanced on a knife edge in terms of energy state and if anything goes wrong, like a bit of inattention or distraction that causes that last bit of surplus energy to be consumed, your only choice is to dive, hard. Even at service ceiling, you have to carefully monitor airspeed. A little bit of smooth down-side mountain wave that starts you descending 100fpm will be corrected by the A/P with a pitch up, which will bleed off speed, and if you are already close to min drag and distracted for enough time, before you know it the shaker is going and the only option is to dive. $\endgroup$– John KJul 15, 2021 at 17:14
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2 Answers
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From prof. Wittenberg's half-a-century-old lecture book, paper copy only, translation and interpretation fully on my account. Way before any A320 family aeroplane...
The pic is relevant for propeller aeroplanes, and indicates a theoretical ceiling (max climb speed = 0) that is about 5% higher than the service ceiling (max climb speed = 100 ft/min). The theoretical ceiling will only be reached after an infinite amount of time, since the climb speed is ever decreasing.
For high subsonic aeroplanes like the B737 and A320 families, there are additional limitations to the max climb speed: $C_{L,max}$ as function of the Mach number is limited by the buffeting boundary. The figure above is referenced in the book as being from a high subsonic aeroplane, which may well be the Fokker 28. Resulting in altitude and M limitations as depicted below.
Note that
- the figure references a turbo engine, not a modern high bypass engine;
- indeed the absolute ceiling can be a tricky point to be at, diving out of it may be limited by the max. buffeting speed.
So, what is the theoretical ceiling of the A320/B737/A220? A couple of percent higher than the service ceiling, unless limited by the max. buffet speed. And it takes forever to get there.
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Absolute ceiling is not a fixed number and may change from flight to flight, and even within the same flight. It depends on conditions at altitude, loading of the aircraft, etc. A lightly loaded aircraft may be able to push the envelope higher than one that is heavily loaded. That is why the number that is published is the service ceiling, which is determined after reviewing flight test results and coming up with a number that incorporates a safety margin for safe aircraft operation.
answered Jul 16, 2021 at 6:50