Definition
A specific implementation of text-based controller-pilot messaging that uses the FANS 1/A protocol (the message standard developed by Boeing and Airbus for oceanic and remote operations) carried over VDL Mode 4, a VHF digital data link that exchanges short messages between aircraft and ground stations on VHF frequencies. Together they let a controller send clearances, instructions, and information to the cockpit as text messages, and let the pilot respond, without using voice radio.
Plain English
A way for controllers and pilots to send each other typed messages instead of talking on the radio. FANS 1/A is the message format, and VDL Mode 4 is the radio channel that carries those messages.
Context Anchor
A pilot may see this in avionics capability requirements, flight planning information, or procedure notes for operations that allow or require data-link communication.
Derivation
CPDLC literally describes what it does: Controller-Pilot Data Link Communications. FANS (Future Air Navigation System) was the industry name given in the 1990s to the next generation of communication, navigation, and surveillance systems designed for global airspace. VDL means VHF Data Link, and Mode 4 is one of several technical versions of that link, each designed for different message types and rates.
Why Pilots Care
Supports faster, clearer communication with air traffic control in busy or oceanic airspace.
Intuition Check
Do not read “Mode 4” as a higher level of pilot skill or a fourth step in a procedure. Here, “mode” means a named technical method that the radio equipment uses to send digital messages.
Example Sentence 1
The aircraft was equipped with CPDLC FANS 1/A VDL Mode 4, allowing the crew to receive their departure clearance as a text message rather than over the voice frequency.
Example Sentence 2
The RNAV departure included a note that CPDLC FANS 1/A VDL Mode 4 was required for the route.