sandyb123
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Flying Over Service Celling?

Sun Jan 03, 2010 1:15 am

Hi all,

Most jet aircraft fly most efficiently fly above 30,000 ft and have a celling around 41,000 ft. What would happen if an aircraft was to fly over it's service celling? I have read this statement:

Quote:
The Next Geneartion Boing 737 is certified to fly up to 41,000 feet -- but in theory, it could go higher if they really wanted to. Military and experimental planes can fly much higher (85-96K). What is really weird is that it seems like the limiting factor at high altitudes is that the air becomes too thin to run the jet engines -- not too thin to continue to provide lift.

Source article

Is that true? Is it possible? Would there be structural / pressurisation issues. How likely is this to happen?

Sandyb123
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EMBQA
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RE: Flying Over Service Celling?

Sun Jan 03, 2010 1:20 am



Quoting Sandyb123 (Thread starter):
What would happen if an aircraft was to fly over it's service celling? I have read this statement:

It could and planes have crashed...... the Pinicale CRJ a few years back comes to mind
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HOOB747
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RE: Flying Over Service Celling?

Sun Jan 03, 2010 1:20 am

Not sure if the higher altitude affects the jet engines, but I'm sure the thinner air at such altitudes affects the control surfaces and their interaction with the atmosphere. Meaning, the higher the elevation, the lower the effectiveness of the control surfaces.
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MGASJO
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RE: Flying Over Service Celling?

Sun Jan 03, 2010 1:23 am

Flight 3701 rings a bell


Pinnacle Airlines Flight 3701
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FighterPilot
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RE: Flying Over Service Celling?

Sun Jan 03, 2010 1:27 am

Have to be careful here, service ceiling and certified ceiling are two different things.
A service ceiling is the height an aircraft can get to and only produce 100FPM. Where as a certified ceiling is the ceiling that the manufacturers have certified it for. So theoretically yes, a plane can climb over both its service and certified ceilings. Not advisable but possible.

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seabosdca
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RE: Flying Over Service Celling?

Sun Jan 03, 2010 2:02 am

Every now and then rumors pop up around here about military variants doing things the civilian aircraft are not certified to do. The most persistent is a rumor that E-4Bs (military 747-200 variants) have climbed as high as 51,000 feet, well above the 747's ceiling of FL450. I've also seen it rumored that non-US operators have had their 757 variants as high as 47,000 feet.

For civilian aircraft, the limiting factor is often the length of time it would take the aircraft to descend to 10,000 feet in the event of a depressurization.

[Edited 2010-01-02 18:03:53]
 
rfields5421
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RE: Flying Over Service Celling?

Sun Jan 03, 2010 2:22 am

Part of the service ceiling is the way the cabin is pressurized.

Lightly loaded aircraft with big engines can get quite high - the B757 comes to mind and one with a favorable power to weight ratio. But I would not want to cruise at FL470 in one.
 
kalvado
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RE: Flying Over Service Celling?

Sun Jan 03, 2010 2:32 am

http://en.wikipedia.org/wiki/Coffin_corner_%28aviation%29
you cannot get infinitely high - you need to keep airspeed above stall but below flow separation.
At some point that becomes impossible.
 
BMI727
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RE: Flying Over Service Celling?

Sun Jan 03, 2010 2:36 am



Quoting RFields5421 (Reply 6):
Part of the service ceiling is the way the cabin is pressurized.

The limiting factor for the BAe 146 was that it could not descend fast enough to go any higher.

Quoting SeaBosDca (Reply 5):
The most persistent is a rumor that E-4Bs (military 747-200 variants) have climbed as high as 51,000 feet, well above the 747's ceiling of FL450.

How often do 747s go above FL410? I know that SPs would regularly operate higher, but I've never heard of that with the other variants.
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Mir
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RE: Flying Over Service Celling?

Sun Jan 03, 2010 3:05 am



Quoting Sandyb123 (Thread starter):
Is that true? Is it possible?

Both, though you certainly won't see a 737 at 85,000 feet - that's U-2 territory.

Quoting Sandyb123 (Thread starter):
Would there be structural / pressurisation issues.

Either that, or the airplane wouldn't be able to descend to a breathable altitude fast enough in case of a depressurization.

The absolute limit is going to be the point at which the low speed limit (not enough air going over the wing to keep the airplane at altitude) and the high speed limit (mach effects) converge. Above that, you simply cannot fly anymore. As one nears that point (known as coffin corner), the range of allowable airspeeds becomes very small, too small for safety in the opinion of the regulators. So they can cap the certified altitude well below that in order to provide an adequate margin for error.

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cpd
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RE: Flying Over Service Celling?

Sun Jan 03, 2010 3:14 am

Quoting BMI727 (Reply 8):
How often do 747s go above FL410?

I think you'll find that B747s on short ferry flights (light loaded) will readily go above FL410. Even the 747-400/ER version. They have massive climb performance in this sort of configuration. But what happens in the event of depressurisation?

That said, I find the article pretty pointless. Comparing military aircraft designed for extreme high altitudes against civil subsonic airliners isn't valid.

Unless you are talking Concorde - because it has achieved FL687 (normal ceiling FL600). Concorde also was able to descend very quickly in comparison with other airliners if needed.

[Edited 2010-01-02 19:18:02 by cpd]

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