You might have heard of an aviation concept called the coffin corner, where an aircraft can stall due to flying too fast and simultaneously air passing too slow over the wings at high altitude. What is the solution, and can it happen to commercial aircraft? Let’s explore.
What is the coffin corner?
The coffin corner is called the Q Corner in the official aviation lexicon, as the letter Q is the symbol for dynamic pressure – the pressure caused by air flowing over the wing. A coffin corner comes into existence as an aircraft moves fast enough and high enough that the pressure starts to equalize between under and over the wing.
If the plane slows down, it will stall as there isn’t enough air pressure to keep it aloft. If the plane speeds up to compensate, you will hit the subsonic Mach limit and the aircraft will pitch down and stall.
This margin of error is so small that a plane flying at 70,000 feet has a buffer of five knots between going too fast and going too slow.
This is because as a plane increases in altitude, the air gets thinner, thus the plane has to move faster the generate lift. When a plane reaches an altitude where it can’t go fast enough to have enough air passing over the wing to generate lift, it becomes difficult to control and could stall.
What can aircraft do to escape it?
If an aircraft finds itself approaching the coffin corner then the only way to escape is to maintain the speed and reduce the altitude. If the speed changes in any way, then the aircraft will stall.
But even a stall isn’t a worst-case scenario. Engines lacking power is not the cause of a stall, rather just the air flowing over the wing. If an aircraft stalls, the pilot lowers the nose of the aircraft using pitch control (elevator control) to decrease the angle of attack and restore laminar flow over the wing.
Are you at risk when flying in a commercial aircraft?
You don’t need to worry about the coffin corner when flying onboard a commercial aircraft for several reasons.
- Pilots are well trained and have experience in stall conditions and how to escape them.
- On board systems will warn pilots if there is any risk of a stall.
That said, it has happened that a commercial aircraft has flown into the corner. Air France Flight 447 crashed due to frozen airspeed sensors that failed to report stall conditions. Whether or not they were in the coffin corner at the time is up for debate, but the flight pattern does indicate that they were no longer generating lift. The silver lining from these events is that pilots today are well versed in conditions and know how to spot the coffin corner.