Which condition is described as coffin corner?

Which condition is described as coffin corner?

• A. Occurs when an aircraft stalls at high altitude
• B. When the aircraft exceeds its structural limit engine
• C. When buffet occurs at speeds above Mach
• D. Occurs when an airplane climbs so high that the margin between stall buffet and Mach buffet approaches zero

Answer: (D)

The condition being tested is the narrowing of the safe speed range at very high altitude where two different buffet limits come close together. Coffin corner happens when the airplane climbs high enough that the margin between the stall buffet limit (when the wing flow starts to separate and lift falls) and the Mach buffet limit (caused by transonic shock and resulting flow disturbance) approaches zero. In this regime the aircraft can reach a stall or experience Mach buffet with very little warning because the speeds that trigger these two phenomena converge. Stall buffet is tied to the wing reaching a critical angle of attack and losing lift, while Mach buffet is tied to transonic airflow and shock-induced buffet as speeds near the speed of sound. As altitude increases, the flight envelope compresses so these two limits come close, making the zero-margin condition the defining feature of coffin corner. Other options describe only a single phenomenon or a different scenario and don’t capture the simultaneous proximity of both stall and Mach buffets at high altitude.

The condition being tested is the narrowing of the safe speed range at very high altitude where two different buffet limits come close together. Coffin corner happens when the airplane climbs high enough that the margin between the stall buffet limit (when the wing flow starts to separate and lift falls) and the Mach buffet limit (caused by transonic shock and resulting flow disturbance) approaches zero. In this regime the aircraft can reach a stall or experience Mach buffet with very little warning because the speeds that trigger these two phenomena converge.

Stall buffet is tied to the wing reaching a critical angle of attack and losing lift, while Mach buffet is tied to transonic airflow and shock-induced buffet as speeds near the speed of sound. As altitude increases, the flight envelope compresses so these two limits come close, making the zero-margin condition the defining feature of coffin corner.

Other options describe only a single phenomenon or a different scenario and don’t capture the simultaneous proximity of both stall and Mach buffets at high altitude.