In a strong wind, groundspeed may vary appreciably during a turn, as, for example, in the case of a landing after a U-turn preceding the localizer intercept. Such conditions are critical for maximum use of the runway, and render human estimation of aircraft motion extremely difficult. This paper summarizes the tests conducted using a ground-based 4D-guidance program, developed to assist the air traffic controller in maintaining the predicted landing-time sequence with an accuracy better than 10 seconds for each arrival.