The crash, which occured close to the West London satellite town of Staines, was, until the Lockerbie disaster of 1988, the worst aircrash to have occurred on British soil.
The aircraft "Papa India" was on a scheduled flight from London to Brussels under the command of Captain Key. During the climb-out from Heathrow, the aircraft was flown at too low a speed, and the leading-edge lift-augmentation droops were prematurely retracted, which led to a series of stalls. The condition was not recognised quickly by the pilots despite the operation of the stick shaker, and the aircraft quickly entered a deep stall, from which there was no possibility of recovery. The aircraft rapidly descended in a high nose-up attitude until striking the ground close to the King George reservoirs on the outskirts of Staines. Unusually, there was no fire on impact.
The question facing the accident investigators was what actually caused the crash - while the reason for the stall was easily determined, after extensive examination of the wreckage and flight recorder, no evidence of any malfunction could be found. However there was an industrial dispute in progress at the time, between the pilot's union BALPA and the airline, BEA. Among the wreckage of Papa India was found a crew table on which was scribbled some offensive graffitti directed at the captain. Prior to the flight, there had been a heated argument in the flight crew room about the desirability or otherwise of strike action, and Captain Key had been involved. An autopsy of the captain revealed some long-standing heart disease, but no actual evidence of a heart-attack or other incapacitation, but the possibility of this, especially given the earlier confrontation, could not be discounted altogether. The official report also examined a number of crew-interaction aspects which it found wanting, Clearly, somebody had moved the droop retraction lever while the aircraft was at too low a speed, but it was impossible to determine who had done it or why. This error would not have caused a crash if it had been quickly recognised and corrected, but this was not done - and in fact the automatic systems that engaged to warn the pilots and correct the stall were overridden, possibly because a number of previous false activations had led the pilots to treat the system as unreliable.
Ultimately the true cause of the accident could not be determined, but the AAIB (Air Accidents Investigation Board) made a series of recommendations regarding operation of the Trident, crew training, cockpit voice recorders and medical examinations which could all have been factors.