It’s a safety feature in some aircraft designed to provide a warning to the pilot if the aircraft is approaching or has entered a stall condition.

The flapper switch stall warning device typically consists of a small vane or flap located on the leading edge of the wing. When the airflow over the wing decreases due to a stall, the vane or flap moves, triggering a warning system that alerts the pilot to take corrective action to prevent a stall. This device helps pilots maintain control of the aircraft, especially during critical phases of flight such as takeoff and landing.

One example of an aircraft equipped with a flapper switch stall warning device is the Cessna 172.