An airstair is a set of steps built into an aircraft so that passengers may board and alight the aircraft. The stairs are often built into a clamshell-style door on the aircraft. Airstairs eliminate the need for passengers to use a mobile stairway or jetway to board or exit the aircraft, providing more independence from ground services. Some of the earliest aircraft to feature airstairs were the Martin 2-0-2 and Martin 4-0-4. Some models of the Douglas DC-3 were also retrofitted with airstairs. As airport infrastructure has developed, the need for airstairs has decreased, as jetways or mobile stairways are often available. Wide-body aircraft rarely employ airstairs, as the doors are significantly higher above the ground than narrow-body aircraft. One notable exception is the Lockheed L-1011, the only wide-body aircraft to feature full-height airstairs. The only other wide-bodies with airstairs, the VC-25 and the Ilyushin Il-86, have airstairs contained in the cargo hold, with steps inside the cabin to access these stairs. Some aircraft, like the Boeing 727 and McDonnell Douglas DC-9, were designed to improve ground services, with passengers deplaning from the front as the aircraft is serviced from the rear, allowing for quicker turnarounds. Airstairs are also used as a security measure, for example on aircraft carrying the President of the United States, allowing the aircraft to be boarded by VIPs at any time - with or without the cooperation of ground services.

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