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TRUE AIRSPEED - The airspeed of an aircraft relative to undisturbed air. Used primarily in flight planning and narrate portion of flight. When used in pilot/controller communications, it is referred to as “true airspeed” and not shortened to “airspeed”.

AIRSTART - The starting of an aircraft engine while the aircraft is airborne, preceded by engine shutdown during training flight or by actual engine failure.
AIR TAXI - Used to describe a helicopter/VTOL aircraft movement conducted above the surface but normally not above 100 feet above ground level. The aircraft may proceed either via hover taxi or flight at speeds more than 20 knots. The pilot is solely responsible for selecting a safe airspeed/altitude for the operation being conducted. (See Hover Taxi) (Refer to 7110.65-972)
AIR TRAFFIC (P/CG) - Aircraft operating in the air or on an airport surface, exclusive of loading ramps and parking areas.
AIR TRAFFIC (ICAO) - All aircraft in flight or operating on the maneuvering area of an aerodrome.
AIR TRAFFIC ADVISORY SERVICE (ICAO) - A service provided within advisory airspace to ensure separation, in so far as possible, between aircraft which are operating on IFR flight plans.
AIR TRAFFIC CLEARANCE/AIR TRAFFIC CONTROL CLEARANCE - 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. (See Air Traffic Control Instructions)

AIR TRAFFIC CONTROL ADVISES - Used to prefix a message of noncontrol information when it is relayed to an aircraft by other than an air traffic controller. (See Advisory)
AIR TRAFFIC CONTROL ASSIGNED AIRSPACE/ATCAA - Airspace of defined vertical/lateral limits, assigned by Air Traffic Control, for the purpose of providing air traffic segregation between the specified activities being conducted within the assigned airspace and other IFR air traffic. (See Alert Area, Military Operations Area, Special Use Airspace)
AIR TRAFFIC CONTROL ASSIGNED AIRSPACE/ATCAA (Federal Aviation Administration 7610.4) - Airspace of defined vertical/lateral limits, normally within Positive Control Area, which is assigned by Air Traffic Control for the purpose of providing air traffic segregation between the specified activities being conducted therein, and other IFR air traffic.
AIR TRAFFIC CONTROL/ATC (P/CG) - A service operated by appropriate authority to promote the safe, orderly and expeditious flow of air traffic.
AIR TRAFFIC CONTROL CLEARANCE - (See Air Traffic Clearance)