Definition
A cockpit warning device that produces an audible tone when the airplane's angle of attack approaches the critical angle at which the wing will stall. It is triggered either by a small movable vane on the wing's leading edge that is pushed up by the changing airflow at high angles of attack, or by an electrical pressure sensor wired to a horn or buzzer in the cabin.
Plain English
A loud beep or buzzing sound in the cockpit that warns the pilot the wing is getting close to stalling. It activates before the stall actually happens, giving the pilot time to react.
Context Anchor
You hear or test the stall horn during preflight checks, slow flight practice, stall training, and sometimes on approach if the airplane gets too slow or the nose is held too high.
Derivation
“Stall” originally means to stop or come to a halt. In aviation, it refers to the wing no longer producing normal lift because the airflow over it is no longer smooth. “Horn” means a sound-making warning device, so a stall horn is the sound warning for an approaching wing stall.
Why Pilots Care
Gives an early, unmistakable alert so the pilot can lower the nose and recover before a full aerodynamic stall develops and control is lost.
Intuition Check
Do not read “stall” here as the engine stopping. A stall horn warns about the wing getting close to losing normal lift, not about the engine quitting.
Example Sentence 1
As the airplane slowed in the landing flare, the stall horn began to chirp just before the main wheels touched down.
Example Sentence 2
During stall recovery practice, the instructor told the student to apply full power as soon as the stall horn activated.