Why do planes crash? How can they be made safer in the future? This is one of the major questions facing air crash detectives - investigators of the Accident Investigation Branch, whose job it is to analyse the cause of every British air disaster throughout the world.

The film shows the investigators at work, analyses unique film of an actual crash at London Airport and re-creates investigations into a number of British air disasters, which, as the detectives point out, are increasingly caused by human error, whether it be pilot fatigue or a mechanic leaving nuts and bolts in the engine. Tonight's programme shows the major contribution of Accident Investigators to the present high standards of air safety.