What is CPDLC and how does it improve ATC communication?

CPDLC (Controller-Pilot Data Link Communications) provides text-based communication between pilots and ATC, complementing voice. Benefits: Reduced voice congestion, Clear unambiguous messages, Message verification and logging, and Enables oceanic/remote area communication. Message types: Clearances, Instructions, Requests, and Information. Architecture: Aircraft CMU/ATSU connects to ground ATSP via VHF or SATCOM datalink. Part of ATN (Aeronautical Telecommunication Network) or FANS (Future Air Navigation System). Implementation: FANS 1/A (Boeing/Airbus) for oceanic, ATN B1/B2 for continental. Message formats per ICAO/RTCA standards. CPDLC mandatory for North Atlantic and increasingly required in high-density airspace. Crew training addresses human factors of mixed voice/data environment.