Airport Elevation/Field Elevation: The highest point of the usable runways measured in feet 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.
Air Traffic Control (ATC): Any of the controlling agencies providing direction and traffic separation for
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
BIT: Built-in test. Self-testing capabilities contained within an instrument or system.
Caution Area: An area within which military training activities, though not hazardous, are of interest to
Ceiling: The height above the earths surface of the lowest layer of clouds or other obscuring
phenomena. This layer is described as broken, overcast, or obscuration and not classified as thin