Definition
A surveillance system in which an aircraft automatically transmits position, altitude, and other flight data to an air traffic control facility under the terms of a pre-arranged agreement, or 'contract,' between the aircraft's avionics and the ATC ground system. The contract specifies what data is sent and when — for example, at fixed time intervals, when the aircraft passes a waypoint, or when a deviation from the planned route occurs. ADS-C is primarily used in oceanic and remote airspace where conventional radar coverage is unavailable.
Plain English
A system where the aircraft automatically reports its position to controllers at agreed times or events, instead of being tracked by radar. It is mainly used over oceans and remote areas where radar cannot reach.
Context Anchor
Seen in instrument procedure, flight planning, and ATC capability discussions, especially for routes or airspace that use digital position reporting instead of normal radar coverage.
Derivation
Automatic' because the aircraft sends the reports without pilot action. 'Dependent' because the position comes from the aircraft's own navigation system, not from an independent ground sensor like radar. 'Surveillance' is the act of monitoring aircraft. 'Contract' refers to the pre-arranged agreement between the aircraft and the ATC system that defines when and what to report.
Why Pilots Care
Enables safe ATC separation and monitoring in areas without radar coverage, supporting efficient routing and reducing the risk of loss of separation on long over-water flights.
Intuition Check
“Contract” does not mean paperwork between the pilot and ATC. Here it means the aircraft and ground systems have agreed on when automatic position reports will be sent.
Example Sentence 1
Once established in oceanic airspace, the crew confirmed that ADS-C reports were being received by the controlling center.
Example Sentence 2
When the ADS-C link activated, the controller immediately saw the aircraft's updated track on the oceanic display.