Definition
A data-link message sent from the aircraft to air traffic control at the pilot's request, rather than as an automatic or controller-prompted transmission. PID messages are used in CPDLC (Controller-Pilot Data Link Communications) and similar data communication systems to send requests, reports, or position information to ATC by selecting the message from a cockpit menu.
Plain English
A message the pilot chooses to send down to air traffic control through the aircraft's data communication system, instead of speaking on the radio.
Context Anchor
Seen in flight deck data-link procedures, where crews send written electronic messages between the aircraft and air traffic control.
Derivation
Pilot Initiated means the pilot starts the action. Downlink means a transmission going down from the aircraft to a ground station — the opposite of an uplink, which is sent from the ground up to the aircraft.
Why Pilots Care
It reduces voice radio congestion and supports clear transmission of requests or reports.
Intuition Check
Do not read “downlink” as meaning the airplane is descending. Here it means information is being sent from the aircraft down to a ground system.
Example Sentence 1
The crew used a PID to request a higher cruising altitude rather than calling on the radio.
Example Sentence 2
Using PID, the crew sent a position report directly to the ground facility.