The Gander Area Control Centre (ACC) is equipped with an Airport Surveillance Radar (ASR5)and a Joint En Route Terminal System (JETS) which is an automated system that provides tracking of secondary surveillance radar data which are displayed to the controller in alphanumeric format. Altitude is determined from Mode C output of the aircraft transponder and indicates in 100-foot increments above sea level. Altitude data are provided to the transponder from either the pilot's or co-pilot's normal static system; true altitude is about 35 feet less than indicated altitude at 165 knots indicated airspeed (KIAS). Ground speed is computed from the smoothed velocity vector and is essentially a weighted average of the track speed.

Radar data are not recorded at Gander. However, the departure controller observed the secondary radar target of the aircraft as it moved down the runway. The data block ground speed increased to 150 knots, and the Mode C altitude readout remained at 500 feet asl throughout the attempted take-off. The target was observed to move to a position about one quarter of a mile beyond the departure end of the runway, where it entered the "coast" mode. At no time did the altitude reading change from its initial reading of 500 feet.