Accident investigators confirmed yesterday that the Concorde airliner which crashed on Tuesday had undergone repairs to its left engine only minutes before its ill-fated take-off - the same engine which caught fire and exploded in the disaster that killed 113 people.
Although Air France claims that work carried out on a thrust reverser in engine 2 - under the left wing - could not have led to the fire and explosion, French aviation experts believe it is more than a coincidence that the fire started there. During routine tests before take-off, the pilot detected an abnormality in the thrust reverser and requested repairs. A flawed part was replaced with one stripped from another Concorde, delaying the aircraft's departure by half an hour.
The engineers who carried out the work are being questioned. If a tool - or even a tiny bolt - is accidentally left in a turbojet, the fans can break, leading to an engine fire and explosion. The intrusion of a bird could have the same effect. A fuel leak is another possible cause under review.
Ms Elisabeth Senot, the deputy public prosecutor who is leading one of two official investigations into the crash, yesterday disclosed the contents of the cockpit flight recorder. "There is a fire on board", the control tower told the pilot as AF4590 was taking off. But the pilot had gained so much speed that he did not have enough runway space to brake without crashing. "Failure of engine 2", the pilot said as the plane began its final plunge.
An amateur video obtained by television networks last night clearly shows that the left engines were on fire immediately after the plane became airborne.
Aviation analysts believe that the twinning of engines under Concorde's wings enabled the fire to spread to another engine.
Normal procedure is for a pilot to shut down an engine which catches fire, take off with power from three engines, discard fuel in the air and circle back to the airport to land safely. This scenario - because it is one of the most dangerous situations in flying - is frequently practised by Concorde crews in training.
But if, as investigators suspect, the fire spread to a second engine, the plane would have lost half of its power and would no longer have had sufficient thrust to climb.
The "black box" has been turned over to Ms Senot, who has asked the specialised air transport gendarmerie at Roissy to carry out the investigation. The technical data from the flight recorder may be deciphered by this evening and Mr Jean-Claude Gayssot, the French Minister of Transport, has suggested that Air France's Concorde flights could restart soon after. Air France grounded its five remaining Concordes after Tuesday's crash. British Airways, which operates seven Concordes, resumed flights yesterday.
Mr Jean-Cyril Spinetta, the chairman of Air France, who witnessed the crash from his airport office, says he believes engine failure was the cause of the disaster. But Rolls Royce, the builder of Concorde's Olympus 593 engine, has cautioned against hasty conclusions.
Mr Spinetta said that four of Air France's six Concordes had tiny cracks due to stress and age in the wings, like those discovered on British Airways' Concordes. But the aircraft which fell from the sky on Tuesday had no cracks, and Mr Spinetta excluded the possibility that wing fissures caused the disaster.
