Definition
A Controller-Pilot Data Link Communications message sent from the aircraft to the air traffic controller. It is the pilot-initiated half of the CPDLC text-message exchange, used to make requests, send reports, or respond to controller messages without using voice radio.
Plain English
A text message the pilot sends to the controller through the aircraft's data link system, instead of speaking on the radio.
Context Anchor
Seen in data link communication procedures, especially when an aircraft sends a request, report, or response to ATC through the flight deck system.
Derivation
Downlink' comes from the idea of a signal going down from the aircraft to the ground station. 'Uplink' is the opposite direction. The term is borrowed from satellite and radio communications, where 'down' always means toward the ground and 'up' means away from it.
Why Pilots Care
Knowing which direction a CPDLC message travels matters because procedures, response requirements, and message logs are organized by uplink vs. downlink. A pilot needs to recognize that anything they send is a downlink, and anything they receive is an uplink.
Intuition Check
Downlink does not mean the aircraft is descending. Here, “down” means the message is being sent from the aircraft toward the ground-based ATC system.
Example Sentence 1
The crew composed a downlink CPDLC message requesting a higher altitude and waited for the controller's response.
Example Sentence 2
Position reports are often transmitted as downlink CPDLC messages during oceanic flights.