Glossary  G-1  Approach Fix. From a database coding standpoint, an  approach fix is considered to be an identifiable point  in space from the intermediate fix (IF) inbound. A fix  located between the initial approach fix (IAF) and the IF is  considered to be associated with the approach transition  or feeder route.  Approach End of Runway (AER). The first portion of the  runway available for landing. If the runway threshold is  displaced, use the displaced threshold latitude/longitude  as the AER.  Air Traffic Service (ATS). Air traffic service is an ICAO  generic term meaning variously, flight information service,  alerting service, air traffic advisory service, air traffic control  service (area control service, approach control service, or  aerodrome control service).  Air Route Traffic Control Center (ARTCC). A facility  established to provide air traffic control service to aircraft  operating on IFR flight plans within controlled airspace and  principally during the en route phase of flight  Airport Surface Detection Equipment-Model X  (ASDE-X). Enables air traffic controllers to detect potential  runway conflicts by providing detailed coverage of movement  on runways and taxiways. By collecting data from a variety of  sources, ASDE-X is able to track vehicles and aircraft on the  airport movement area and obtain identification information  from aircraft transponders.  Airport Sketch. Depicts the runways and their length, width,  and slope, the touchdown zone elevation, the lighting  system installed on the end of the runway, and taxiways.  Airport sketches are located on the lower left or right  portion of the instrument approach chart.  Abeam Fix. A fix, NAVAID, point, or object positioned  approximately 90 degrees to the right or left of the aircraft  track along a route of flight. Abeam indicates a general  position rather than a precise point.  Accelerate-Stop Distance Available (ASDA). The runway  plus stopway length declared available and suitable for  the acceleration and deceleration of an airplane aborting a  takeoff.  Advanced Surface Movement Guidance and Control  System (A-SMGCS). A system providing routing, guidance  and surveillance for the control of aircraft and vehicles,  in order to maintain the declared surface movement rate  under all weather conditions within the aerodrome visibility  operational level (AVOL) while maintaining the required  level of safety.  Aircraft Approach Category. A grouping of aircraft based  on reference landing speed (V$_{REF}$), if specified, or if V$_{REF}$ is  not specified, 1.3 V$_{SO}$ (the stalling speed or minimum steady  flight speed in the landing configuration) at the maximum  certificated landing weight.  Airport Diagram. A full-page depiction of the airport that  includes the same features of the airport sketch plus  additional details, such as taxiway identifiers, airport  latitude and longitude, and building identification. Airport  diagrams are located in the U.S. Terminal Procedures  booklet following the instrument approach charts for a  particular airport.  Airport/Facility Directory (A/FD). Section within the Chart  Supplement regional booklets published by Aeronautical  Information Services that provides information about all  airports in the region. The A/FD section includes runway  length and width, runway surface, load bearing capacity,  runway slope, airport services, and hazards, such as birds  and reduced visibility. 