airport surface detection equipment. See ASDE.
airport surveillance radar. See ASR.
airport taxi charts. Aeronautical charts designed to expedite safe and efficient flow of ground traffic at an airport.
airport traffic area. Normally, the airspace within a horizontal radius of five statute miles from the geographical center of any airport having an operating control tower. An airport traffic area extends upward from the surface to, but not including, an altitude of 3,000 feet above the elevation of the airport.
air route surveillance radar. See ARSR.

air route traffic control center. See ARTCC.
air scoop. A hooded opening used to direct outside air into an aircraft structure in flight. The ram effect caused by movement of the aircraft through the air increases the amount of air taken into the structure.
airscrew. The British term for an aircraft propeller.
air seal. A seal around a rotating shaft, used to keep air from passing out of the housing holding the shaft. Air seals are often made of thin alternate fixed and rotating blades which act as air dams to prevent air flowing past the seal.
airship. 14 CFR Part 1: “An engine-driven lighter-than-air aircraft that can be steered.”
airspace. The space above a certain geographical area.
airspeed. The rate at which an aircraft is moving through the air.
airspeed indicator. A differential air pressure gage which measures the difference between ram, or impact, air pressure and the local static air pressure. The dial of an airspeed indicator is calibrated to convert this differential air pressure into units of knots, miles per hour, or kilometers per hour.
air start (aircraft engine operation). The process of starting an aircraft engine in flight with the engine rotated by aerodynamic forces acting on the propeller or compressor blades.
air taxi (helicopter operation). Movement of a helicopter above the surface but at an altitude of less than 100 feet above ground level.
air traffic. 14 CFR Part 1: “Aircraft operating in the air or on an airport surface, exclusive of loading ramps and parking areas.”
air traffic clearance. 14 CFR Part 1: “An authorization by air traffic control, for the purpose of preventing collision between known aircraft, for an aircraft to proceed under specified traffic conditions within controlled airspace.”
air traffic control. The control of aircraft traffic from the ground. Air traffic control is done from control towers whose personnel direct air traffic in the vicinity of an airport and air route traffic control centers whose personnel direct air traffic along the airways between airports.