Coffin Corner

[ZAGORFLY]

DO you guys think that a sort of BRS parachute could be developed to slow down (temporary) an uncontrolled upset flight attitude situation? Could this maybe too simple cheap idea ever saved the GOL 737 over the recent collision in Brazil?

Nowadays airlines want to fly higher as possible to save fuel regardless the danger of coffin corner. You may save fuel not lives is something goes wrong isn't?

[DC-8]

Originally Posted by ZAGORFLY

Nowadays airlines want to fly higher as possible to save fuel regardless the danger of coffin corner. You may save fuel not lives is something goes wrong isn't?

An aircraft must fly at the optimum FL. If you fly above that FL you will also have a fuel penalty; it would only be economical if you have a considerably increase in tail wind. Other reason to fly above the optimum is to avoid meteorological adversities.

So, why would airlines want to fly higher?

[chornedsnorkack]

Originally Posted by DC-8

Other reason to fly above the optimum is to avoid meteorological adversities.

So, why would airlines want to fly higher?

GOL is a bad example. Look at the Pulkovo Tu-154, though.

Attempted flying over a thundercloud, near its ceiling. Whether it was also trying to turn around the weather or whether it hit a gust above the cloud, the - structurally intact - plane seems to have entered a flat spin. The plane never recovered and impacted ground.

[dartagnan]

they want fly high, to get direct route and avoid traffic!
some business jets can go up to fl450....

[chornedsnorkack]

Originally Posted by Janspeed

Hi there,
By the looks of it, it tried to go ABOVE it's ceiling and then stalled and spun.....

True. But a point of safety is that it entered uncontrolled and unrecoverable upset mode of stall and spin - it did not sink a bit and resume normal flight.

[RobertS975]

Originally Posted by dartagnan

they want fly high, to get direct route and avoid traffic!
some business jets can go up to fl450....

I believe that some Lears are certified to FL510.

[Mad (Flt) Scientist]

Originally Posted by RobertS975

I believe that some Lears are certified to FL510.

Lear 40 and 45 are, as two examples. Not sure of the earlier models.

Global Express and derivatives are also cleared to 51000ft

[gearpins]

is the ceiling is limited due to the factors related to press,like delta p,max cab alt,time taken for emergency descend..or thrust related?

[camprax]

What exactly is a coffin corner?Is it the same as tuck under?
Turboprops dont get that fast!
tks

[Mudfoot]

Camprax, here's your answer (thanks, Google tm search)

Coffin corner
From Wikipedia, the free encyclopedia
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Coffin corner is a term used in three different fields architecture, aircraft operation and sports, primarily American football and Canadian football.

Contents
1 Architecture
2 Football
3 Aircraft operation
3.1 Mach Limit
3.2 Stall Limit
3.3 The Corner


Aircraft operation
Coffin corner is a dangerous portion of the flight envelope that must be carefully approached by high altitude high subsonic speed aircraft, such as the Lockheed U-2 aircraft.


Mach Limit
A subsonic aircraft must not exceed its Mach limit, some fraction of the speed of sound near, but not at 1.0. At the low air densities and lower temperatures encountered at high altitude the speed of sound is lower. Exceeding the Mach limit can cause loss of control and/or structural failure.


Stall Limit
At high altitudes the low density air is less capable of supporting the aircraft and so the stall speed increases (as expressed in true air speed).


The Corner
At some limiting altitude these speeds converge, and the aircraft cannot be flown, as a slight pitch down will cause the Mach limit to be exceeded while a slight pitch up will cause an aircraft stall with a subsequent pitch down.

Retrieved from "http://en.wikipedia.org/wiki/Coffin_corner"

Cheers, y'all.

[Mad (Flt) Scientist]

Originally Posted by gearpins

is the ceiling is limited due to the factors related to press,like delta p,max cab alt,time taken for emergency descend..or thrust related?

Be careful with terminology. The aircraft are cleared to an altitude, therefore their certified maximum altitude is as stated, and this is presented as a "Limitation" in the Aircraft Flight Manual, Pilot Manual, or equivalent.

This need not be a true 'limit' on the aircraft's capabilities; it's possible that there is no hard boundary at FL510, simply that the OEM has not pushed the certification beyond that point. While an optimised design shouldn't have much margin left at the edges of the envelope, you can't necessarily reverse engineer the actual capability of an aircraft from any published limitations. Everyone likes to keep a little something in their back pocket, and there's no way to be sure exactly how full that pocket is.