Coffin Corner?

[Splash]

Saw or read this term somewhere recently and would like to know what it means.  I know it has something to do with buffetting
Cheers
Splash

[Ivan]

altitude where your IAS is equal or lower than your stall speed at your wingtips.
If you turn around, you will get into a stall (and probably spin) as one wing will go slower, loses lift and drops down

[Nexus]

Coffin corner occurs at an aircrafts absolute ceiling, where the speeds at which mach number buffet and prestall buffet occur, are the same

For a constant mach number, the IAS decreases with altitude due to decreaing LSS. To prevent the IAS from deacreasing to its stall speed, the mach number must be increased, which results in an increase in IAS.
But if you fly a constant IAS (in climb), the mach number will be increased to a point where it exceeds Mcrit, to prevent this from happen the IAS must be reduced.

So simply put, there comes a point at the aircrafts absolute ceiling where the aircraft can't go any higher. Because it is bounded

[cableguy]

ok now all this in english plz

[Nexus]

okay...imaging you're balancing on a thin board:

It is a balance act allright...If you fall to the left you will fry in the fire of hell.
However if you fall to the right you will instead freeze to death in the cold ocean.

That's the difference...if you fly slower, you will drop out of the sky, if you fly faster some part of the airflow (if not all parts) over the wings will be supersonic, hence creating  a dramatic increase in drag coefficient.

[cableguy]

ok gotcha  ;)

[Splash]

So it's that very fine line between highspeed buffett and low speed buffet?  I can understand why they call it Coffin Corner.  Ah, and the Deadman Zone in a chopper.
Cheers
Splash

[Craig.]

i thought it was a punt that goes out of bounds within the 5 yard line

[Nexus]

Splash, regarding the "line" between Stall and supersonic:
In real life, the mach number buffet and prestall buffet are difficult to extinguish between, that's why a margin is imposed between an aircraft's operating ceiling and its maximum (absolute) ceiling.