CPDLC

Controller–pilot data link communications (CPDLC) is a data link system that enables text-based exchanges of air traffic control (ATC) messages between pilots and controllers. It supplements or replaces portions of voice radio communications, particularly for clearances, routing, altitude and speed instructions, holds, and operational messages. CPDLC relies on the aeronautical data-link infrastructure, commonly using ACARS over VHF Datalink Mode 2 or satellite links.

CPDLC messages are drawn from a standardized ATS message set established by ICAO. Typical interactions include a controller sending a departure clearance or route amendment, altitude or speed constraints, and hold instructions; the pilot can acknowledge, request changes, or issue routine position reports. Messages are presented in a standardized format in the cockpit and require explicit acknowledgment to confirm receipt and intent.

Implementation and standards: CPDLC is part of ICAO’s CNS/ATM modernization and is standardized in ICAO documentation such as Doc 4444 and related materials. It is deployed in European airspace, the North Atlantic, and other regions, with ongoing efforts to improve interoperability. CPDLC uses data-link networks (VDL Mode 2 or SATCOM) and commonly the ACARS transport layer. The system supports real-time exchanges as well as delays when voice channels are unavailable.

Benefits and limitations: CPDLC reduces frequency congestion, minimizes miscommunication, and can shorten turnaround times by delivering clearances and instructions directly to the cockpit. It provides a verifiable audit trail and supports more efficient traffic flows in busy or remote airspace. Limitations include the need for compatible avionics and ground systems, crew and controller training, and potential delays if crew action or message validation is required.

History: CPDLC emerged in the 1990s as part of CNS/ATM modernization. Early operational use occurred in Europe and the North Atlantic, with broader deployment in subsequent decades as aircraft and ground systems were upgraded. Ongoing work focuses on interoperability, security, and integration with other surveillance and communication systems.