ACooper vane (also sometimes called aDan Cooper switch orD.B. Cooper device) is a mechanicalaerodynamicwedge that prevents the ventralairstair of an aircraft from being lowered in flight.[1]
In the United States, following threehijackings in 1972, theFederal Aviation Administration ordered thatBoeing 727 aircraft be fitted with Cooper vanes.[2] The device was named for an unidentified airplane hijacker dubbedD. B. Cooper, who used the rear airstair to exit a Boeing 727 in flight and make aparachute escape.
The Cooper vane is a very simple device: It consists of a spring-loaded paddle connected to a plate that prevents the ventralairstair of an aircraft from being lowered in flight.[1] When the aircraft is on theramp, the spring keeps the paddle perpendicular to thefuselage, and the attached plate does not block the stairway. As the aircraft takes off, the airflow pushes the paddle parallel to the fuselage and the plate is moved underneath the stairway, preventing it from being lowered. Once the airflow decreases on landing, the spring-loaded paddle returns to its initial position, thereby allowing the stairs to be lowered again.
McDonnell Douglas DC-9 aircraft with ventral stairs were also equipped with Cooper vanes.