The need to put many more aeroplanes safely in any given airspace sector implies smaller separations and much greater flying accuracy in all four dimensions, including time. That can be achieved only by pre-programming air-traffic-control computers with the aircraft's flight plan, and having the aircraft's flight-management system (FMS) continually feed back its performance, position and the crew's intentions through data-links.
The ATC computer can correlate that feedback with similar data from other aircraft in the sector, and up-link corrections or amendments to the aircraft's trajectory for input direct into the aircraft's FMS after they are "accepted" by the pilot.
Pilots can downlink to ATC desired changes in trajectory, entered into the system via the control and display unit. Once those changes are cleared or amended by the ATC computer, they are up-linked for acceptance by the pilot and entry into the FMS.
The navigation display is similar to a standard one, but the way-points are annotated with precise times and acceptable deviations, from the ideal 4-D trajectory can be displayed (as described in the main text).
Source: Flight International
