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 AREA- 

(See SPECIAL USE AIRSPACE.) 

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. 

