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Flying Over Service Celling?  
User currently offlineSandyb123 From UK - Scotland, joined Oct 2007, 1133 posts, RR: 0
Posted (4 years 12 months 2 hours ago) and read 5673 times:
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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


Member of the mile high club
10 replies: All unread, jump to last
 
User currently offlineEMBQA From United States of America, joined Oct 2003, 9364 posts, RR: 11
Reply 1, posted (4 years 12 months 2 hours ago) and read 5656 times:



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



"It's not the size of the dog in the fight, but the size of the fight in the dog"
User currently offlineHOOB747 From United States of America, joined Nov 2006, 449 posts, RR: 0
Reply 2, posted (4 years 12 months 2 hours ago) and read 5656 times:

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.


747 Number One Fan from U.S.A
User currently offlineMGASJO From Nicaragua, joined Feb 2005, 466 posts, RR: 7
Reply 3, posted (4 years 12 months 2 hours ago) and read 5639 times:

Flight 3701 rings a bell


Pinnacle Airlines Flight 3701



C208B
User currently offlineFighterPilot From Canada, joined Jun 2005, 1418 posts, RR: 22
Reply 4, posted (4 years 12 months 2 hours ago) and read 5618 times:

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.

Cal  airplane 



*Insert Sound Of GE90 Spooling Up Here*
User currently offlineSeaBosDca From United States of America, joined Sep 2007, 5856 posts, RR: 6
Reply 5, posted (4 years 12 months 1 hour ago) and read 5499 times:

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]

User currently offlineRFields5421 From United States of America, joined Jul 2007, 7607 posts, RR: 32
Reply 6, posted (4 years 12 months 1 hour ago) and read 5428 times:

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.


User currently offlineKalvado From United States of America, joined Feb 2006, 498 posts, RR: 0
Reply 7, posted (4 years 12 months 1 hour ago) and read 5410 times:

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.


User currently offlineBMI727 From United States of America, joined Feb 2009, 15842 posts, RR: 27
Reply 8, posted (4 years 12 months 1 hour ago) and read 5398 times:



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.



Why do Aerospace Engineering students have to turn things in on time?
User currently offlineMir From United States of America, joined Jan 2004, 21880 posts, RR: 55
Reply 9, posted (4 years 12 months ago) and read 5289 times:



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.

-Mir



7 billion, one nation, imagination...it's a beautiful day
User currently offlineCpd From Australia, joined Jun 2008, 4881 posts, RR: 37
Reply 10, posted (4 years 12 months ago) and read 5249 times:

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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