What does the term "Coffin Corner" refer to?

The term "Coffin Corner" refers to the intersection of stall speed and maximum operating speed, which occurs at high altitudes where the air density decreases. In this scenario, the margins between the stall speed (the minimum speed at which an aircraft can maintain level flight) and the maximum operating speed (the maximum speed the aircraft can safely fly) become very narrow.

At a certain altitude, as an aircraft climbs higher, the stall speed can increase while the maximum operating speed also decreases due to changes in air density, creating a "corner" where pilots must operate very carefully. If the aircraft exceeds this narrow band of speed, it risks either stalling or exceeding structural limits. Understanding Coffin Corner is crucial for pilots, particularly during high-altitude operations, as it emphasizes the need for precise speed management to ensure safety in flight.