Coffin Corner describes?

• A. Coffin Corner refers to high altitude operations when Mmo approaches True Stall Speed; narrow speed window.
• B. Coffin Corner is a type of cargo hold.
• C. Coffin Corner occurs at sea level.
• D. Coffin Corner is a turbulence phenomenon.

Answer: (A)

Coffin Corner is about the dangerous narrowing of the safe flight speed range at very high altitudes. As you climb, the maximum operating Mach number drops while the true stall speed (the speed at which the wing actually stalls) doesn’t stay far away. That means the speeds you can fly between—the stall edge and the Mach limit—get closer together. When Mmo approaches the true stall speed, there’s only a tiny window to stay safely within; a small change in power or pitch can push you into a stall or into an overspeed with buffet. This is why it’s described as Coffin Corner—the airplane can get trapped between two dangerous limits. It isn’t about cargo holds, sea level behavior, or turbulence, which is why those options don’t describe this high-altitude speed conflict.