An airstair is a passenger staircase that is built in to an airliner — often, though not always, on the inside of a clamshell-style door. The stairs can be raised or lowered while the aircraft is on the ground, allowing passengers and ground personnel to board or depart the aircraft without the need for a mobile staircase or a jetway. The widest use of Airstairs was on the Boeing 727 & 737. Airstairs have become less common because of increasing airport infrastructure, but they are still popular on small regional airliners and aircraft which operate into less-well equipped airports.
Due to the height of the doors above the ground, airstairs are almost never incorporated into wide-bodied and long-range aircraft. The only wide-body ever to have the option for a full-height built-in airstair was the Lockheed L-1011. The only other wide bodies to feature airstairs (the Ilyushin Il-86 and Boeing VC-25) use the alternate method of building the airstair into the cargo compartment, and then having more stairs inside to the main deck of the aircraft.
The airplane hijacker D. B. Cooper escaped via an airstair. Subsequently, Cooper vanes were installed to keep the airstair from being deployed in flight. Ventral airstairs incorporated into the Boeing 727 and McDonnell Douglas DC-9 designs were particularly efficient from a ground handling perspective, for as passengers were deplaning aircraft, cleaners could be servicing the aft lavatories and moving forward, maintaining the aircraft cabin and facilitating more thorough and quicker aircraft turn arounds. Quicker turn around benefits airline, as this allows for greater daily aircraft utilization and thus potentially more profits. Modern airline executive accountants analyze cost benefit penalties of the fractionally increased overall aircraft weight which such designs impose.
Airstairs provide aircraft with a degree of independence from ground services that can be useful in special circumstances. For example, the aircraft used by the President of the United States are equipped with a full complement of airstairs to ensure that the aircraft can be boarded under any circumstances at any airport, with or without cooperation or presence of ground support.
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