As used in this manual, the following abbreviations/ acronyms have the meanings indicated. Appendix 3. Abbreviations/Acronyms AIM 8/15/19 Appendix 3 − 1 Abbreviations/Acronyms Abbreviation/ Acronym Meaning AAWU ..... Alaskan Aviation Weather Unit AAS ....... Airport Advisory Service AC ........ Advisory Circular ACAR ..... Aircraft Communications Addressing and Reporting System ADCUS .... Advise Customs ADDS ...... Aviation Digital Data Service ADF ....... Automatic Direction Finder ADIZ ...... Air Defense Identification Zone ADS − B..... Automatic Dependent Surveillance − Broadcast AFB ....... Air Force Base AFCS ...... Automatic Flight Control System AFIS ....... Automatic Flight Information Service AFM....... Aircraft Flight Manual AGL ....... Above Ground Level AHRS ...... Attitude Heading Reference System AIM ....... Aeronautical Information Manual AIRMET . . . Airmen’s Meteorological Information AIS ........ Aeronautical Information Services ALD ....... Available Landing Distance ALDARS . . . Automated Lightning Detection and Reporting System ALS ....... Approach Light Systems AMSL ..... Above Mean Sea Level ANP ....... Actual Navigation Performance AOCC ..... Airline Operations Control Center AP ........ Autopilot System APV ....... Approach with Vertical Guidance AR ........ Authorization Required ARENA .... Areas Noted for Attention ARFF IC .... Aircraft Rescue and Fire Fighting Incident Commander ARINC ..... Aeronautical Radio Incorporated ARO ....... Airport Reservations Office ARSA ...... Airport Radar Service Area ARSR ...... Air Route Surveillance Radar ARTCC..... Air Route Traffic Control Center ARTS ...... Automated Radar Terminal System ASDE − X ... Airport Surface Detection Equipment  − Model X ASOS ...... Automated Surface Observing System ASR ....... Airport Surveillance Radar Abbreviation/ Acronym Meaning ASRS ...... Aviation Safety Reporting System ASSC Airport Surface Surveillance Capability ATC ....... Air Traffic Control ATCRBS .... Air Traffic Control Radar Beacon System ATCSCC .... Air Traffic Control System Command Center ATCT ...... Airport Traffic Control Tower ATD ....... Along − Track Distance ATIS ....... Automatic Terminal Information Service ATT ....... Attitude Retention System AWC....... Aviation Weather Center AWOS ..... Automated Weather Observing System AWTT ..... Aviation Weather Technology Transfer AWW ...... Severe Weather Forecast Alert BAASS ..... Bigelow Aerospace Advanced Space Studies BBS ....... Bulletin Board System BC ........ Back Course BECMG .... Becoming group C/A........ Coarse Acquisition CARTS..... Common Automated Radar Terminal System (ARTS) (to include ARTS IIIE and ARTS IIE) CAT ....... Clear Air Turbulence CD ........ Controller Display CDI........ Course Deviation Indicator CDR ....... Coded Departure Route CERAP ..... Combined Center/RAPCON CFA ....... Controlled Firing Area CFIT ....... Controlled Flight into Terrain CFR ....... Code of Federal Regulations COA ....... Certificate of Waiver or Authorization CPDLC ..... Controller Pilot Data Link Communications CTAF ...... Common Traffic Advisory Frequency CVFP ...... Charted Visual Flight Procedure CVRS ...... Computerized Voice Reservation System CWA....... Center Weather Advisory CWSU ..... Center Weather Service Unit DA ........ Decision Altitude DCA ....... Ronald Reagan Washington National Airport DCP ....... Data Collection Package DER ....... Departure End of Runway DH ........ Decision Height