Definition
A surveillance system in which an aircraft automatically transmits position, altitude, time, and other flight data to an air traffic services unit under the terms of a pre-arranged contract between the aircraft's avionics and the ground system. The contract specifies what data is sent and how often — for example, periodic reports at set intervals, event-driven reports when the aircraft crosses a waypoint, or on-demand reports requested by the controller. ADS-C is used primarily in oceanic and remote airspace where conventional radar coverage is unavailable.
Plain English
The aircraft and the ground station agree in advance on what flight information will be sent and when. The aircraft then sends those reports automatically, usually over satellite, so controllers can track flights in places where radar cannot reach.
Context Anchor
Pilots usually encounter ADS-C in oceanic, remote, or other areas where normal radar coverage is limited or unavailable.
Derivation
Automatic — the reports are sent without pilot action. Dependent — the data depends on the aircraft's own navigation systems (rather than being independently measured by ground radar). Surveillance — tracking an aircraft's position. Contract — a formal agreement between aircraft and ground system specifying the reporting terms. The 'contract' part is the key idea: it is not a continuous live feed like radar, but a negotiated arrangement of what gets sent and when.
Why Pilots Care
It allows ATC to maintain accurate surveillance and issue timely instructions on long flights over water or unpopulated areas, reducing separation requirements and improving safety.
Grounding Statement
Picture an aircraft far offshore automatically sending regular position updates to air traffic control because radar cannot reach that far.
Intuition Check
“Contract” does not mean a legal paperwork agreement here. It means an agreed automatic reporting arrangement between the aircraft system and the air traffic control system.
Example Sentence 1
Before entering oceanic airspace, the crew confirmed an ADS-C contract had been established with the controlling center.
Example Sentence 2
Because the ADS-C link was active, controllers received automatic position updates every ten minutes without voice calls.