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-established agreement, or contract, between the aircraft and the ground system. Reports are sent at intervals or in response to specific events defined by that contract, and the system is primarily used in oceanic and remote airspace where radar coverage is not available.
Plain English
It is a way for an aircraft to automatically send its position and flight information to controllers based on a set agreement about when and what to send. It is mainly used in places where radar cannot reach, like over oceans.
Context Anchor
Seen in oceanic, remote, and international operations where pilots may be outside normal radar coverage and position reports are handled by digital messages.
Derivation
Automatic — the aircraft sends data on its own without a pilot request. Dependent — the position information depends on the aircraft's own navigation systems rather than ground radar. Surveillance — watching or tracking the aircraft's movement. Contract — a pre-arranged agreement between the aircraft and the ground station that defines what data is sent and when. The word contract here clarifies the difference from ADS-B (Broadcast), where data is sent continuously to anyone listening rather than to a specific party under set terms.
Why Pilots Care
Provides ATC with reliable position data for separation in areas without radar coverage, supporting safe long-distance flights over oceans and remote regions.
Intuition Check
Do not read contract here as a business or legal agreement. In this term, contract means the aircraft and ground system have an agreed pattern for what reports will be sent and when.
Example Sentence 1
Crossing the North Atlantic, the crew confirmed their ADS-C contract was active with the oceanic control center before leaving radar coverage.
Example Sentence 2
Position reports were sent automatically every fourteen minutes under the active contract.