Definition
A surveillance system in which an aircraft automatically transmits position, altitude, time, 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 ground system. The contract specifies what information is sent and when — for example, at fixed time intervals, on reaching a waypoint, or when certain events occur such as a deviation from the cleared route or altitude. ADS-C is primarily used in oceanic and remote airspace where radar coverage is not available.
Plain English
The aircraft and the controller agree in advance on what flight information the aircraft will send and how often. The aircraft then sends those reports automatically, without the pilot having to do anything each time.
Context Anchor
Seen in oceanic and remote-area operations where controllers may rely on data link position reports instead of radar.
Derivation
Automatic' because the reports are sent without pilot action. 'Dependent' because the position data depends on the aircraft's own navigation systems (typically GPS) rather than being measured independently by ground radar. 'Surveillance' because controllers use it to track aircraft. 'Contract' because the reporting terms are agreed in advance between the aircraft and the ATC system, rather than being a continuous broadcast.
Why Pilots Care
Allows controllers to maintain safe aircraft separation and efficient routing in areas without radar coverage, directly supporting continued flight in oceanic and remote regions.
Grounding Statement
In simple terms, ADS C is the aircraft checking in automatically with air traffic control at agreed times or when agreed conditions occur.
Intuition Check
Contract does not mean a business or legal agreement here. In ADS C, it means the reporting rule that tells the aircraft when to send information to the ground system.
Example Sentence 1
Before entering oceanic airspace, the crew confirmed that the ADS-C contract with the controlling center had been established and that periodic position reports were being sent automatically.
Example Sentence 2
ATC established an ADS-C contract with a ten-minute reporting interval to monitor the flight through the remote airspace.