What phenomenon is referred to as coffin corner?

The term "coffin corner" refers specifically to the area between maximum operating speed (Vmo) and stall speed (Vs) of an aircraft. As altitude increases, both these speeds can converge, creating a narrow range where the aircraft is at risk of stalling if it slows down too much, or exceeding its structural limits if it speeds up too much. This situation is particularly critical because pilots must manage their airspeed with great precision to avoid these risks, making the concept of coffin corner essential for safe flight operations, especially in high-altitude conditions.

In this context, knowing the boundaries defined by maximum operating speed and stall speed is vital for pilots, as operating in this zone can lead to dangerous flight conditions. The concept highlights the challenges of flying in certain altitude bands, emphasizing the need for appropriate speed management to ensure safety and performance.