Watching the Discovery Channel Curiosity episode “plane crash” reminds me of working on the B-727 as a young mechanic and the “D.B. Cooper Vane” installed to prevent the rear airstairs from being opened in-flight.
On November 24, 1971, a man calling himself Dan Cooper purchased a one way ticket on Northwest Airlines flight 305 from Portland to Seattle. After takeoff he presented a note demanding $200,000 upon their arrival in SEA otherwise he would explode a bomb he had with him. After receiving the money and parachutes the aircraft departed SEA and subsequently the man lowered the aft airstairs and jumped out over Washington state.
After the event in 1972 the FAA required all operators of the Boeing 727 to install a spring loaded hinged vane device to prevent the aft airstairs from being lowered in flight thus eliminating the possibility of “copy cat” parachuting skyjackers.
The simple device allows the stairs to be deployed on the ramp but when the aircraft takes off, the airflow pushes the paddle parallel to the fuselage and the plate is moved underneath preventing the stairs from being lowered. Occasionally the vanes would not retract and mechanics would have to go out and physically move it to release the stairs. Low on fuel, the 727 was very tail heavy so it was important to deploy the stairs while parked and unloading the forward cargo bins,
Douglas DC 9 aircraft with aft ventral air stairs were also equipped with Cooper vanes.
The Discovery Channel show doesn’t mention it but they obviously had to deactivate the “DB Cooper Vane”