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A Cooper Vane is a security device which is fitted onto aircraft with built in sets of stairs, known as “Airstairs.” Most aircraft do not have Airstairs anymore, because they are designed to taxi up to terminals, and at small airports, airport staff will wheel out a stairway for passengers to use. The Cooper Vane prevents the Airstair from being engaged while the plane is in flight.
The inspiration for the Cooper Vane was a hijacker named D.B. Cooper, who hijacked a plane in 1971. After demanding money and parachutes, Cooper apparently lowered the rear Airstair of the plane and escaped. Cooper and the money were never seen again, suggesting that the ploy may not have been entirely successful, but observers noted that the Airstair in the Boeing 727, the type of aircraft Cooper hijacked, was particularly vulnerable to this type of activity. Most of the main cabin doors would be extremely difficult to open in mid air, but the rear Airstairs on the 727 series jets were ideal for mid-air escapes.
In 1972, numerous hijackings occurred, and some of them followed the Cooper model. In response, the Federal Aviation Administration mandated that the Cooper Vane had to be installed on aircraft equipped with Airstairs. Some airlines chose to dispose with Airstairs altogether in response to the problem, while others installed the device for airplane protection.
The mechanism behind a Cooper Vane is relatively simple. It consists of a paddle shaped piece of metal attached to a spring. When the aircraft is on the ground, the metal projects perpendicularly out from the plane, allowing the Airstairs to be raised and lowered at will. Once the plane is airborne, air pressure pushes against the device, forcing it flat against the fuselage of the aircraft. The Cooper Vane is positioned so that when it flattens out, it will lock the Airstair from the outside. When the airplane lands, the reduced airflow allows the device to pop back out so that the Airstair can be lowered.
Many other safety measures have been implemented to make commercial aircraft less susceptible to hijacking. The Cooper Vane is only one such safety measure, and on a well maintained modern aircraft, numerous other safeguards are in place, such as locks on the doors leading to the flight deck. Commercial airlines attempt to reduce their vulnerability by combining mechanical measures with passenger screening and an alert, well-trained crew. Hijacking countermeasures have greatly reduced the number of annual hijackings in nations which use them.