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. Some piston-era airliners were equipped with airstairs, including the Martin 2-0-2, Martin 4-0-4, and versions of the Douglas DC-3 specially modified in the 1940s by Southwest Airways. 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.
Ventral airstairs are featured on most tail-engined airliners, such as the Boeing 727, McDonnell Douglas DC-9, McDonnell Douglas MD-80, BAC 1-11 and Yakovlev Yak-40/Yak-42 series, and are incorporated as ramps which lower from the fuselage. The Ilyushin Il-86 has three airstairs on the port side.
The most common type of airstair is found in most business aircraft, regional jets and other small airliners, which is a stair built into the inside of a door, which is lowered to the outside. This design is efficient and because the aircraft which use it sit low to the ground, the design can stay simple and not add complexity or weight to the design, one of the biggest problems with airstair assemblies. The design has also been used with a single-length set of extension stairs on aircraft such as the cargo compartment of the widebody Ilyushin Il-86 (the primary entrance to the aircraft for passengers), Boeing VC-25, and the belly lounges of three Lockheed L-1011s.
Another widespread type of airstair is used for forward doors. The stair folds and stows under the floor of the door and is deployed from the fuselage immediately below the forward door. This type of airstair is found on many short-range aircraft such as Boeing 737s, DC-9s, and some Airbus A320 series aircraft. The mechanism is also quite heavy; as a result, many airlines have removed this system to reduce aircraft weight.
A unique airstair design was used for the aft doors of 737 Combi aircraft, which consisted of a clamshell door which dropped down to open much like a business aircraft, but then had stairs which were stored trifold in the curve of the door, which would unfold to the ground. This system was very cumbersome, was very susceptible to damage, and thus has been removed by many of its users.
The most unusual airstair design was found on the Lockheed L-1011, which was a full-height airstair which was stored in a cargo compartment and allowed access from the right aft passenger door to the ground. This design was ultimately so large and heavy, and it took up valuable cargo space, that it was rarely used.
The original On-Board Folding Airstairs were designed by Winters Aircraft Engineering Company over 30 years ago. Airweld Incorporated is the current STC holder and has FAA PMA for all of the original STC’s issued to Winters, as well as STC’s issued to subsequent manufactures including Kaiser Aerospace, WAPCO and Advanced Aerospace. The On-Board Folding Airstairs can be found in use on many U.S. and Foreign Military and Government Aircrafts including the Boeing E4B as well as VIP aircrafts around the world. The On-Board Folding Airstairs is a multi-section (3, 4 or 5 segment) airstair that can be installed at either the Forward, Center or Aft doors. When retracted/closed, the airstair sits on a track and is typically stowed in a closet either Forward, Aft or Transverse.