A fire drill delayed a routine inspection of the runway which Concorde used for its doomed flight that killed 113 people last month, the chief French investigator said yesterday.
A preliminary report said a metal strip found on the runway was likely to have burst one of the Concorde's tyres, triggering a chain of events that caused the airliner to crash in flames less than two minutes after take-off on July 25th.
"There was a firemen's drill and the runway inspection was postponed," Mr Paul-Louis Arslanian, head of the Air Accident Investigation Bureau (BEA), told a news conference held to present the report.
Mr Arslanian said airport staff routinely inspect the runway three times a day, but on July 25th a third check was postponed.
An inspection was carried out at 4.30 a.m., followed by a partial inspection of the west side of the runway at noon, which was followed by the fire drill. The ill-fated Air France Concorde took off at 4.43 p.m.
"Like you, I am obviously surprised that the third inspection did not take place. Of course it is normal for us to raise this question. But we don't have an answer yet," Mr Arslanian said, warning against drawing hasty conclusions.
"For the time being nothing has been established. We need to understand what was done during the firemen's exercise."
The Paris Airport Authorities' director of communication and the environment, Mr Didier Hamon, said the "firemen conducting the exercises were professionals" who would have reported any problems on the runway.
The 43-centimetre metal strip, bent at one end and punched with rivet holes, looked like an aircraft part, said Mr Arslanian. Its origin had not been established although some of the planes that had used the runway before Concorde had been inspected.
"I am confident that if someone finds out it fell off his plane, he will not conceal it," Mr Arslanian said.
Since the beginning of the investigation, experts have speculated that the metal strip, painted red on one side and yellow on another, caused the tyre to explode.
Debris from the tyre is then thought to have ruptured the fuel tanks, setting off a fire that trailed a plume of flames behind the aircraft as it plunged into a hotel in Gonesse on the outskirts of Paris.
"During the takeoff, the front right tyre of the main left undercarriage was destroyed, very likely by passing over a piece of metal," said the report, which contained a photograph of a shredded Concorde tyre with a 32-centimetre tear.
Mr Arslanian said identifying the origin of the metal piece was not a priority as investigators tried to determine the precise cause of the disaster, the first fatal Concorde accident in 24 years of commercial flight.
"What is important is to know what has happened, to determine the scenario which linked the destruction of the tyre to the fire or understand what caused the disturbances of the engines."
Also in question, said Mr Arslanian, was the Concorde's burst tyre, which was still to be analysed by investigators.
"It is not the make of tyre that is in question, but the Concorde tyre itself," he said. "There is definitely a problem linked to the Concorde tyre."
Mr Arslanian added that it could take "months, even years" for investigators to establish a final report on the causes of the accident.
On the fate of the Concorde, Mr Arslanian said he was "unable to make long-term hypotheses" and said the decision on whether the plane would fly again would not be taken by the BEA.
The British and French air safety authorities suspended Concorde's certificates of airworthiness earlier last month until the risk from tyre blowouts was addressed.
Experts will continue their investigation into the accident and the Franco-British working group that is to decide the fate of Concorde will meet again on Thursday.