3/21/24 

Pilot/Controller Glossary 

AUTOMATED TERMINAL PROXIMITY ALERT (ATPA)

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 Monitors the separation of aircraft on the Final 

Approach Course (FAC), displaying a graphical notification (cone and/or mileage) when a potential loss of 

separation is detected. The warning cone (Yellow) will display at 45 seconds and the alert cone (Red) will display 

at 24 seconds prior to predicted loss of separation. Current distance between two aircraft on final will be 

displayed in line 3 of the full data block of the trailing aircraft in corresponding colors. 
AUTOMATED WEATHER SYSTEM

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 Any of the automated weather sensor platforms that collect weather data 

at airports and disseminate the weather information via radio and/or landline. The systems currently consist of 

the Automated Surface Observing System (ASOS) and Automated Weather Observation System (AWOS). 
AUTOMATED UNICOM

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 Provides completely automated weather, radio check capability and airport advisory 

information on an Automated UNICOM system. These systems offer a variety of features, typically selectable 

by microphone clicks, on the UNICOM frequency. Availability will be published in the Chart Supplement and 

approach charts. 
AUTOMATIC ALTITUDE REPORT

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(See ALTITUDE READOUT.) 

AUTOMATIC ALTITUDE REPORTING

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That function of a transponder which responds to Mode C 

interrogations by transmitting the aircraft’s altitude in 100-foot increments. 
AUTOMATIC CARRIER LANDING SYSTEM

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 U.S. Navy final approach equipment consisting of precision 

tracking radar coupled to a computer data link to provide continuous information to the aircraft, monitoring 

capability to the pilot, and a backup approach system. 
AUTOMATIC DEPENDENT SURVEILLANCE (ADS) [ICAO]

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 A surveillance technique in which aircraft 

automatically provide, via a data link, data derived from on

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board navigation and position fixing systems, 

including aircraft identification, four dimensional position and additional data as appropriate. 
AUTOMATIC DEPENDENT SURVEILLANCE

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BROADCAST (ADS-B)

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 A surveillance system in which 

an aircraft or vehicle to be detected is fitted with cooperative equipment in the form of a data link transmitter. 

The aircraft or vehicle periodically broadcasts its GNSS

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derived position and other required information such 

as identity and velocity, which is then received by a ground

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based or space

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based receiver for processing and 

display at an air traffic control facility, as well as by suitably equipped aircraft. 

(See AUTOMATIC DEPENDENT SURVEILLANCE

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BROADCAST IN.) 

(See AUTOMATIC DEPENDENT SURVEILLANCE

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BROADCAST OUT.) 

(See COOPERATIVE SURVEILLANCE.) 
(See GLOBAL POSITIONING SYSTEM.) 
(See SPACE

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BASED ADS

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B.) 

AUTOMATIC DEPENDENT SURVEILLANCE

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BROADCAST IN (ADS

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B In)

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 Aircraft avionics capable 

of receiving ADS

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B Out transmissions directly from other aircraft, as well as traffic or weather information 

transmitted from ground stations. 

(See AUTOMATIC DEPENDENT SURVEILLANCE

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BROADCAST OUT.) 

(See AUTOMATIC DEPENDENT SURVEILLANCE

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REBROADCAST.) 

(See FLIGHT INFORMATION SERVICE

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BROADCAST.) 

(See TRAFFIC INFORMATION SERVICE

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BROADCAST.) 

AUTOMATIC DEPENDENT SURVEILLANCE

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BROADCAST OUT (ADS

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B Out)

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 The transmitter 

onboard an aircraft or ground vehicle that periodically broadcasts its GNSS

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derived position along with other 

required information, such as identity, altitude, and velocity. 

(See AUTOMATIC DEPENDENT SURVEILLANCE

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BROADCAST.) 

(See AUTOMATIC DEPENDENT SURVEILLANCE

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BROADCAST IN.) 

AUTOMATIC DEPENDENT SURVEILLANCE

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CONTRACT (ADS

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C)

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 A data link position reporting 

system, controlled by a ground station, that establishes contracts with an aircraft’s avionics that occur 

automatically whenever specific events occur, or specific time intervals are reached. 

PCG A

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