Definition
A text-based controller-pilot messaging system that uses the FANS 1/A protocol delivered over the VHF Data Link Mode 2 network. It allows ATC and the flight crew to exchange clearances, requests, and reports as digital messages instead of voice radio calls, primarily over continental airspace where VHF coverage exists.
Plain English
A way for controllers and pilots to send each other short text messages through the airplane's radio system, instead of talking over the radio. FANS 1/A is the message format, and VDL Mode 2 is the digital radio channel that carries the messages.
Context Anchor
Seen in advanced instrument procedure and RNAV departure discussions where clearances or route changes may be sent electronically to the aircraft.
Derivation
CPDLC is a plain description of what it does: controller-pilot data link communications. FANS came from an ICAO committee in the 1980s tasked with designing the Future Air Navigation System, and the 1/A version is the message set used by Boeing and Airbus aircraft. VDL Mode 2 is simply the second mode of VHF Data Link — a digital signal sent over normal aviation VHF frequencies.
Why Pilots Care
Reduces voice frequency congestion and allows precise, recorded clearances that can be loaded directly into the flight management system.
Analogy
It is like receiving an official written instruction through a secure cockpit messaging system instead of hearing it over a busy radio frequency. The message is still an air traffic control instruction, not casual text.
Grounding Statement
Picture a departure clearance appearing as a message on the flight deck display, with the crew reviewing it before accepting it.
Intuition Check
Do not treat this as a navigation system by itself. It is a communication method used to send and receive control messages; the aircraft still navigates using its approved navigation equipment.
Example Sentence 1
After pushback, the crew received their departure clearance through CPDLC FANS 1/A VDL Mode 2 and loaded the route directly into the FMS.
Example Sentence 2
ATC issued a reroute via CPDLC FANS 1/A VDL Mode 2 while the crew was still on the ground.