Extreme High Altitude Flight—Tales from the Coffin Corner

The “coffin corner” is the region of atmospheric flight where the stall speed and critical Mach number of a subsonic fixed-wing aircraft converge near the same value. Near the coffin corner, any increase in airspeed will subject the plane to buffeting, loss of lift, and loss of control due to supersonic air flow over the wings and control surfaces, while reduction in airspeed will cause the wing to stall and lose lift. The U-2 reconnaissance airplane routinely operated near the coffin corner, with as little as 5 knots between stall speed and the onset of Mach buffet. Even if the pilot maintains airspeed within the narrow permissible band, consider the effect of a turn: the outboard portion of the wing inside the turn may stall while simultaneously the outside wing goes supersonic; this is bad.

Two approaches to extreme high-altitude flight are light and slow, such as the Airbus Zephyr solar powered aircraft, which use an enormous wing allowing them to fly very slowly while avoiding stall, and hot and fast, such as the Concorde airliner and SR-71, which simply blow through the transonic region and cruise well above the speed of sound.


For me, October 25,1999 sticks in my brain: pro golfer Payne Stewart died at 41,000 feet.

We are frail and vulnerable “up there”.


That’s because hypoxia, a different problem than John describes, is subtle with a slow leak, and TUC is short with an explosive decompression. I’ve gone through numerous chamber rides, and the one time I took off my helmet to adjust my nape strap at 25,000 feet, my first signs of hypoxia were quite quick. Indeed, while I recognized them as hypoxia signs, I didn’t really believe I would be hypoxia quite so fast (WAY quicker than in the chamber!), just for grins I put my mask over my face and took a breath - and they all went away instantly.