this animation cracks me up: Animation showing how D. B. Cooper left the hijacked airplane; now, the Cooper vane makes this impossible.

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.[1] In the United States, following three hijackings in 1972, the Federal Aviation Administration ordered that Boeing 727 aircraft be fitted with Cooper vanes.[2] 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.

https://en.wikipedia.org/wiki/Cooper_vane