Definition
A surveillance technology in which an aircraft automatically transmits its position, altitude, velocity, and other data — derived from onboard navigation systems such as GPS — to ground stations and, in some implementations, to other aircraft. Air traffic control and other users receive this information without needing to interrogate the aircraft with radar.
Plain English
The aircraft figures out where it is using its own navigation equipment, and then automatically broadcasts that position to controllers and, in some cases, to other aircraft nearby.
Context Anchor
Seen in discussions of modern aircraft tracking, air traffic control, and equipment that reports an aircraft’s position without a voice report from the pilot.
Derivation
The name describes how the system works. 'Automatic' — it sends data on its own without being asked. 'Dependent' — it depends on the aircraft's own navigation equipment to know where it is, rather than being tracked externally by radar. 'Surveillance' — the function being performed: keeping watch on aircraft positions.
Why Pilots Care
It enables more accurate and frequent position reporting than radar alone, improving situational awareness and reducing collision risk.
Intuition Check
Do not read “dependent” as meaning weak or unreliable. Here it means the tracking information depends on the aircraft’s own position source, rather than being measured entirely from the ground.
Example Sentence 1
Flying across the North Atlantic, the crew relied on automatic dependent surveillance to report their position to controllers throughout the oceanic crossing.
Example Sentence 2
Automatic dependent surveillance data helps air traffic control maintain separation in busy airspace.