Aerodynamic stalls can happen at different altitudes and speeds. One specific type is called a high incidence stall, which occurs at high altitudes and low speeds. This term helps us distinguish it from another type of stall known as a Mach stall. The Mach stall happens when shock waves form as the aircraft exceeds its critical Mach number. At higher altitudes, the speeds for both types of stalls get closer together. This leads to a point on the Flight Envelope diagram known as coffin corner, where the characteristics of these stalls intersect.
