A surveillance protocol in which an aircraft's position and status reports are transmitted to air traffic control under an agreed contract defining reporting triggers, used primarily in oceanic and remote airspace lacking radar coverage, typically carried over a satellite datalink.

Key Points

Operates under a negotiated "contract" between the aircraft and air traffic control specifying reporting triggers — periodic intervals, specific events, or on-demand requests — rather than continuously broadcasting position to any receiver in range
Transmits reports specifically to the contracting air traffic control facility over a datalink connection, typically satellite-based in oceanic and remote airspace, rather than broadcasting openly to all nearby receivers
The primary surveillance mechanism in airspace without radar coverage — oceanic and remote continental areas — where ADS-B's line-of-sight ground station or satellite reception model doesn't provide the same coverage
Commonly deployed alongside CPDLC as part of a FANS-equipped aircraft's oceanic operating capability, since the two together provide both the surveillance (ADS-C) and communication (CPDLC) functions oceanic controllers rely on in place of radar and voice
Reporting frequency is negotiated based on operational need rather than fixed, letting a controller request more frequent updates for closer monitoring or accept a lower default cadence for routine oceanic transit

Concept

Rather than continuously broadcasting position for any receiver to pick up, an ADS-C-equipped aircraft establishes a contract with the specific air traffic control facility responsible for the airspace it's transiting, agreeing on when reports will be sent — at fixed intervals, upon specific events like a route change, or on direct request. The aircraft then fulfills that contract over its datalink connection, giving the controlling facility the surveillance picture it needs without requiring the aircraft's position to be openly broadcast the way ADS-B does.

Explainer

The contract-based, datalink-delivered design of ADS-C exists specifically to solve surveillance in exactly the airspace where radar and open broadcast reception aren't practical options — oceanic and remote continental airspace has no radar coverage and often no ground infrastructure capable of receiving an open ADS-B broadcast, but a satellite datalink connection can reach an aircraft essentially anywhere, making contract-based reporting over that link the practical surveillance solution for controllers responsible for that airspace. This is why ADS-C and CPDLC are so commonly deployed together as a matched pair rather than independently: oceanic controllers need both a way to see where aircraft actually are (ADS-C) and a way to communicate instructions to them (CPDLC), and both functions share the same underlying datalink infrastructure challenge that radar coverage and VHF voice solve for continental airspace instead. For CE aviation verticals, ADS-C capability is a direct prerequisite for reduced oceanic separation standards and modern oceanic traffic management — airspace without ADS-C-equipped traffic must rely on more conservative procedural separation, making ADS-C equipage a genuine capacity and efficiency factor for operators flying oceanic routes regularly.

Cite this entry

ADS-C. ConnectedEarth Knowledge Base. https://connectedearth.space/knowledge-base/ads-c/ (updated 13 September 2026).