Pilot/Controller Glossary Pilot/Controller Glossary  8/15/19 1/30/20  image on a tower display. Used to augment visual  observation by tower personnel of aircraft and/or  vehicular movements on runways and taxiways.  There are three ASDE systems deployed in the NAS:  a.  ASDE-3- a Surface Movement Radar.  b.  ASDE-X- a system that uses an X-band  Surface Movement Radar, multilateration, and  ADS-B.  c.  Airport Surface Surveillance Capability  (ASSC)- A system that uses Surface Movement  Radar, multilateration, and ADS-B.  AIRPORT SURVEILLANCE RADAR- Approach  control radar used to detect and display an aircraft's  position in the terminal area. ASR provides range and  azimuth information but does not provide elevation  data. Coverage of the ASR can extend up to 60 miles.  AIRPORT TAXI CHARTS- (See AERONAUTICAL CHART.)  AIRPORT TRAFFIC CONTROL SERVICE- A  service provided by a control tower for aircraft  operating on the movement area and in the vicinity of  an airport.  (See MOVEMENT AREA.)  (See TOWER.)  (See ICAO term AERODROME CONTROL  SERVICE.)  AIRPORT TRAFFIC CONTROL TOWER- (See TOWER.)  AIRSPACE CONFLICT- Predicted conflict of an  aircraft and active Special Activity Airspace (SAA).  AIRSPACE FLOW PROGRAM (AFP)- AFP is a  Traffic Management (TM) process administered by  the Air Traffic Control System Command Center  (ATCSCC) where aircraft are assigned an Expect  Departure Clearance Time (EDCT) in order to  manage capacity and demand for a specific area of the  National Airspace System (NAS). The purpose of the  program is to mitigate the effects of en route  constraints. It is a flexible program and may be  implemented in various forms depending upon the  needs of the air traffic system.  AIRSPACE HIERARCHY- Within the airspace  classes, there is a hierarchy and, in the event of an  overlap of airspace: Class A preempts Class B, Class  B preempts Class C, Class C preempts Class D, Class  D preempts Class E, and Class E preempts Class G.  AIRSPEED- The speed of an aircraft relative to its  surrounding air mass. The unqualified term  “airspeed” means one of the following:  a.  Indicated Airspeed- The speed shown on the  aircraft airspeed indicator. This is the speed used in  pilot/controller communications under the general  term “airspeed.”  (Refer to 14 CFR Part 1.)  b.  True Airspeed- The airspeed of an aircraft  relative to undisturbed air. Used primarily in flight  planning and en route portion of flight. When used in  pilot/controller communications, it is referred to as  “true airspeed” and not shortened to “airspeed.”  AIRSTART- The starting of an aircraft engine while  the aircraft is airborne, preceded by engine shutdown  during training flights or by actual engine failure.  AIRWAY- A Class E airspace area established in the  form of a corridor, the centerline of which is defined  by radio navigational aids.  (See FEDERAL AIRWAYS.)  (See ICAO term AIRWAY.)  (Refer to 14 CFR Part 71.)  (Refer to AIM.)  AIRWAY [ICAO]- A control area or portion thereof  established in the form of corridor equipped with  radio navigational aids.  AIRWAY BEACON- Used to mark airway segments  in remote mountain areas. The light flashes Morse  Code to identify the beacon site.  (Refer to AIM.)  AIT- (See AUTOMATED INFORMATION  TRANSFER.)  ALERFA (Alert Phase) [ICAO]- A situation wherein  apprehension exists as to the safety of an aircraft and  its occupants.  ALERT- A notification to a position that there  is an aircraft-to-aircraft or aircraft-to-airspace  conflict, as detected by Automated Problem  Detection (APD).  ALERT NOTICE (ALNOT)- A request originated  by a flight service station (FSS) or an air route traffic  control center (ARTCC) for an extensive commu- nication search for overdue, unreported, or missing  aircraft.  ALERT AREA- (See SPECIAL USE AIRSPACE.)  PCG A-9 