AIR TRAFFIC CONTROL

An air traffic control system includes a trajectory prediction module for calculating a trajectory for each aircraft, for inputting aircraft detected position data, and for recalculating the trajectories based on said position data, and a conflict detector for detecting, based on the trajectories, future circumstances under which pairs of aircraft violate predetermined proximity tests, and for causing a display on the display device indicating said circumstances. The systems uses a first proximity test and a second, more restrictive, proximity test; and displays a symbol representing pairs of aircraft which violate the second test in a first mode, and those which violate the first set but not the second set in a second mode.