Description / Abstract: DO-256 defines minimum human factors requirements and guidelines for air traffic services (ATS) data link communications between air traffic specialist and a pilot utilizing Aeronautical Telecommunications Network (ATN). The scope is the initial Controller-Pilot Data Link Communications (CPDLC) capabilities, which comprise the Build I and Build IA phases of the United States implementation path. CPDLC initial communications capabilities will generally encompass the transition and cruise phases of flight and be implemented in Air Route Traffic Control Centers (ARTCCs).