Definition
A surveillance system in which an aircraft automatically transmits its position and other flight data—derived from its onboard navigation systems (typically GPS)—to ground stations or other aircraft, without requiring a pilot action or a controller request. It is 'automatic' because the data is sent without intervention, and 'dependent' because the accuracy of the surveillance depends on the aircraft's own navigation equipment rather than on a ground-based radar measurement.
Plain English
The aircraft works out where it is using its own navigation equipment and automatically sends that information to controllers and nearby aircraft, instead of being tracked from the ground by radar.
Context Anchor
Seen in air traffic surveillance, aircraft equipment, and position-reporting discussions.
Derivation
Automatic = sent without pilot action. Dependent = the position report depends on the aircraft's own navigation system being accurate. Surveillance = watching where aircraft are. Naming it this way distinguishes it from radar, where the ground equipment independently measures the aircraft's position.
Why Pilots Care
Provides real-time traffic information, supports reduced separation standards, and improves safety and efficiency in controlled airspace.
Intuition Check
Do not read “dependent” as meaning unreliable. Here it means the surveillance report depends on information produced by the aircraft’s own onboard equipment.
Example Sentence 1
Over the North Atlantic, the crew's position was tracked through ADS rather than radar.
Example Sentence 2
Air traffic control used ADS information to provide traffic advisories to the flight.