Abstract: The invention relates to a method and apparatus for providing pilots of aircraft or the like with: information about the presence, identification and relative location of, and time to potential collision with, other aircraft, objects, and obstructions, i.e. pilot warning indicator (PWI); instructions enabling pilots to avoid collisions, i.e. a collision avoidance system (CAS); and, advisory messages such as altitude and heading changes. The information, instructions and messages are organized, in accordance with the invention, through the use of a novel program subroutine in a general-purpose digital computer serving as a central communications computer or a specially programmed computer dedicated to controlling the encoding and transmission of digital air traffic control messages to pilot and/or controller information display terminals.