look at this thing!
A Cooper vane (also sometimes called a Dan Cooper switch or D.B. Cooper device) is a mechanical aerodynamic wedge that prevents the ventral airstair of an aircraft from being lowered in flight. In the United States, following three hijackings in 1972, the Federal Aviation Administration ordered that Boeing 727 aircraft be fitted with Cooper vanes. The device was named for an unidentified airplane hijacker dubbed D. B. Cooper, who used the rear stairway to exit a Boeing 727 in flight and make his escape via parachute.