The theory that a piece of debris on the runway caused the crash of the Air France Concorde in July 2000 has been confirmed by French investigators.

The conclusion is part of a 400-page report by France's Accident Investigation Bureau (BEA) into the incident, which left 113 people dead.

Investigators believe this piece of metal triggered the accident

In a statement, the BEA said a stray part lost by a plane that had taken off five minutes earlier punctured one of the Concorde's tyres and triggered the chain of events that caused it to burst into flames and crash.

The investigators said that even if the pilots had managed to abort the take-off, the aircraft would have gone off the runway and burst into flames.

The full report has yet to be released, but French newspaper Liberation said that in it the BEA criticised Air France for its maintenance system - although this had not contributed to the accident.

Air France has denied the media report, saying there was nothing new in the final version of the BEA's report, but that the authorities had made a series of recommendations which had already been implemented.

Safety modifications

According to what is expected to be the final investigation into the tragedy, one of the plane's tyres burst after running over a piece of debris on the runway.

The explosion sent rubber pieces hurtling towards fuel tanks, prompting a fuel leak and the fire that led the plane to crash into a hotel just minutes after taking off from Charles de Gaulle airport.

Investigators have made 13 safety recommendations, many of which have been carried out.

These are reported to include the lining of fuel tanks with bullet-proof Kevlar, a reinforced undercarriage and better black boxes.

After the crash, Concorde - which is only flown by Air France and British Airways - was grounded for 15 months.

It resumed commercial flights again on 6 November.

During that period engineers worked on redesigning elements of the plane and making safety modifications, including new tyres.

Engineers say the flaws that led to the crash have been fixed.