Definition
A surveillance technique in which an aircraft automatically transmits, via a data link, information derived from its onboard navigation and position-fixing systems. This information includes the aircraft identification, four-dimensional position (latitude, longitude, altitude, and time), and additional data as appropriate. ADS is used by air traffic services, particularly in oceanic and remote airspace where conventional radar coverage is unavailable.
Plain English
The aircraft automatically sends its identity, position, altitude, and time to air traffic control over a data link, using its own onboard equipment to work out where it is. Controllers see the aircraft without needing radar.
Context Anchor
Seen in air traffic control, surveillance, ADS-B, ADS-C, and remote or oceanic operations where aircraft position information is sent electronically.
Derivation
The name describes how it works. Automatic — the aircraft sends the report on its own, with no controller request. Dependent — the report depends on the aircraft's own navigation systems being accurate; ATC is not measuring the position independently. Surveillance — ATC is watching the traffic. Together: the aircraft watches itself and tells ATC.
Why Pilots Care
It allows accurate tracking in areas without radar coverage, supports reduced separation standards, and improves situational awareness for both pilots and controllers.
Intuition Check
Do not read “dependent” as meaning the pilot must manually report the position. Here it means the system depends on the aircraft’s own equipment to provide the information.
Example Sentence 1
On the North Atlantic crossing, the crew's position reports were sent automatically through ADS rather than by voice.
Example Sentence 2
Before departure the pilot confirmed the ADS equipment was operational for the assigned route.