Originally Posted by
kenbuck
What does this mean "coffin corner".
At any altitude, if you go too slow, you stall - loss of control.
At any altitude, if you go too fast either you run into flutter (very bad) or hit high Mach effects such as buffet.
So the operational range must lie between the two limiting speeds.
The two speeds get closer together, the higher you go, until eventually they meet.
At that point (called "coffin corner"), if you slow down, you stall, and if you speed up you get nasty Mach effects. Proverbial rock and hard place situation.