CPDLC

Controller Pilot Data Link Communications (CPDLC) is a two-way data-link system by which controllers can transmit non-urgent 'strategic messages to an aircraft as an alternative to voice communications. The message is displayed on a flight deck visual display.

CPDLC was first implemented in Europe by Eurocontrol's Maastricht Upper Airspace Control Centre. Since then, many other ANSPs worldwide have implemented CPDLC in their ACCs. Nowadays, most aircraft flying as GAT above FL285 within the Single European Sky (SES) must be CPDLC equipped (with a few exceptions).