Airport Advisory Area: The area within ten statute miles of an airport without a control tower or where
the tower is not in operation and on which a flight service station is located.
Airport Elevation/Field Elevation: The highest point of an airports usable runways measured in ft MSL.
Airport Surveillance Radar (ASR): Radar providing position of aircraft by azimuth and range data
without elevation data. Used for terminal approach and departure control. (See Surveillance Approach.)
Air Route Traffic Control Center (ARTCC): A facility established to provide traffic control service to IFR
flights operating within controlled airspace, principally during the enroute phase of flight.
Airway: Class E airspace or portion thereof established in the form of a corridor equipped with radio
Alert Area: An airspace which may contain a high volume of pilot training activities or an unusual type of
aerial activity, neither of which is hazardous to aircraft.
Alternate Airfield: An airport specified in a flight plan to which a flight may proceed if the destination is
below minimums or safety considerations preclude a landing.
AOA: Angle of attack.
AOB: Angle of bank.
Approach Control: A term used to indicate an air traffic control unit providing approach control service,
without specifying the unit.
Approach Control Service: Service provided by a terminal area traffic control facility for arriving and/or
departing IFR flights and, on occasion, VFR flights.
ASR: See Airport Surveillance Radar.
ATC: See Air Route Traffic Control Center.
Automatic Terminal Information Service (ATIS): A continuous broadcast of recorded, non-control
information in selected high activity terminal areas. Its purpose is to improve controller effectiveness and
to relieve frequency congestion by automating the repetitive transmission of essential but routine