Pilot/Controller Glossary  12/31/20  PILOT/CONTROLLER  GLOSSARY  PURPOSE  a.  This Glossary was compiled to promote a common understanding of the terms used in the Air Traffic  Control system. It includes those terms which are intended for pilot/controller communications. Those terms  most frequently used in pilot/controller communications are printed in  bold italics . The definitions are primarily  defined in an operational sense applicable to both users and operators of the National Airspace System. Use of  the Glossary will preclude any misunderstandings concerning the system's design, function, and purpose.  b.  Because of the international nature of flying, terms used in the Lexicon, published by the International  Civil Aviation Organization (ICAO), are included when they differ from FAA definitions. These terms are  followed by “[ICAO].” For the reader's convenience, there are also cross references to related terms in other parts  of the Glossary and to other documents, such as the Code of Federal Regulations (CFR) and the Aeronautical  Information Manual (AIM).  c.  This Glossary will be revised, as necessary, to maintain a common understanding of the system.  EXPLANATION OF CHANGES  g.  Editorial/format changes were made where necessary. Revision bars were not used due to the insignificant  nature of the changes.  d.  Terms Added:  e.  Terms Deleted:  f.  Terms Modified:  AUTOMATED EMERGENCY DESCENT  EMERGENCY AUTOLAND SYSTEM  EMERGENCY DESCENT MODE  STNR ALT RESERVATION  TELEPHONE INFORMATION BRIEFING SERVICE  TIBS  TRANSCRIBED WEATHER BROADCAST (TWEB)  TWEB  GROSS NAVIGATION ERROR (GNE)  GROUND COMMUNICATION OUTLET (GCO)  STATIONARY RESERVATIONS  PCG-1 