Definition
A surveillance system in which an aircraft automatically transmits position and other flight data to an air traffic control facility under a pre-arranged agreement, called a contract, that specifies what information is sent and when. The contract may trigger reports at set time intervals, when the aircraft passes a defined waypoint, when it deviates from its planned route or altitude, or on demand from the controller. ADS-C is primarily used in oceanic and remote airspace where conventional radar coverage is not available.
Plain English
The aircraft and the controlling agency set up an agreement in advance about what flight information the aircraft will send and how often. The aircraft then automatically sends those reports — its position, altitude, and so on — over a data link, so controllers can track it in places where radar cannot reach.
Context Anchor
Seen in oceanic and remote-area operations where normal radar coverage may not be available.
Derivation
‘Automatic’ means the reports are sent without the pilot having to do anything each time. ‘Dependent’ means the surveillance depends on the aircraft’s own navigation system to know where it is — controllers are not measuring the aircraft from the ground. ‘Surveillance’ means watching or tracking. ‘Contract’ is used in its agreement sense: the ground station and the aircraft agree in advance on the terms of reporting.
Why Pilots Care
It supplies ATC with reliable aircraft position data in areas without radar, supporting safe separation and efficient routing on long flights.
Analogy
ADS-C is like sharing your location with someone under a specific update rule, such as “send my location every five minutes” or “send it if I change course.” It is not a public broadcast; it is a directed report to the system that has the contract.
Grounding Statement
In remote airspace, ADS-C gives ATC automatic position reports from the aircraft even when radar cannot see it.
Intuition Check
“Contract” does not mean a legal document signed by the pilot. In ADS-C, it means a reporting agreement between aircraft equipment and the ATC system that controls when automatic reports are sent.
Example Sentence 1
Before entering oceanic airspace, the crew confirmed that an ADS-C contract had been established with the controlling center.
Example Sentence 2
ATC revised the ADS-C contract to add event-based reports whenever the aircraft changed altitude or deviated from its cleared route.