Pilot/Controller Glossary 

3/21/24 

AIRSPACE RESERVATION

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 The term used in oceanic ATC for airspace utilization under prescribed conditions 

normally employed for the mass movement of aircraft or other special user requirements which cannot otherwise 

be accomplished. Airspace reservations must be classified as either “moving” or “stationary.” 

(See MOVING AIRSPACE RESERVATION) 
(See STATIONARY AIRSPACE RESERVATION.) 
(See ALTITUDE RESERVATION.) 

AIRSTART

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 The starting of an aircraft engine while the aircraft is airborne, preceded by engine shutdown during 

training flights or by actual engine failure. 
AIRWAY

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 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]

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A control area or portion thereof established in the form of corridor equipped with radio 

navigational aids. 
AIRWAY BEACON

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 Used to mark airway segments in remote mountain areas. The light flashes Morse Code 

to identify the beacon site. 

(Refer to AIM.) 

AIS

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(See AERONAUTICAL INFORMATION SERVICES.) 

AIT

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(See AUTOMATED INFORMATION TRANSFER.) 

ALERFA (Alert Phase) [ICAO]

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 A situation wherein apprehension exists as to the safety of an aircraft and its 

occupants. 
ALERT

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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

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(See SPECIAL USE AIRSPACE.) 

ALERT NOTICE (ALNOT)

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 A request originated by a flight service station (FSS) or an air route traffic control 

center (ARTCC) for an extensive communication search for overdue, unreported, or missing aircraft. 
ALERTING SERVICE

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 A service provided to notify appropriate organizations regarding aircraft in need of 

search and rescue aid and assist such organizations as required. 
ALNOT

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(See ALERT NOTICE.) 

ALONG

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TRACK DISTANCE (ATD)

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 The horizontal distance between the aircraft’s current position and a fix 

measured by an area navigation system that is not subject to slant range errors. 
ALPHANUMERIC DISPLAY

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 Letters and numerals used to show identification, altitude, beacon code, and 

other information concerning a target on a radar display. 
ALTERNATE AERODROME [ICAO]

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 An aerodrome to which an aircraft may proceed when it becomes either 

impossible or inadvisable to proceed to or to land at the aerodrome of intended landing. 

Note: The aerodrome from which a flight departs may also be an en-route or a destination alternate aerodrome 

for the flight. 

ALTERNATE AIRPORT

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An airport at which an aircraft may land if a landing at the intended airport becomes 

inadvisable. 

(See ICAO term ALTERNATE AERODROME.) 

PCG A

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