The accident is due to a series of facts, one or two being perfectly known, but in between we still lack some details on what happened

BEA director Paul-Louis Arslanian

It included a transcript of conversations in the cockpit of the doomed aircraft showing that the crew was unaware of the engine fire which brought the plane down until alerted by the control tower.

All 109 passengers and crew, and four people on the ground, were killed when the New York-bound jet crashed into a hotel in Gonesse on the outskirts of Paris in July.

A fire broke out under the plane's left wing

At Friday's news conference, BEA officials showed a photograph of the 43-centimetre (17-inch) strip of metal from the Paris runway which may have punctured the Concorde's tyres.

The inquiry team is investigating whether the runway was properly swept on the morning of the crash.

"There was a firemen's drill and the runway inspection was postponed," BEA director Paul-Louis Arslanian told a news conference to present its preliminary report.

However the BEA insists the crash was the result of a chain of events and it will be a long time before the full underlying causes of the crash are discovered.

Only then can the BEA make recommendations about modifications which might allow Concorde to fly again.

Too late... no time

Pilot Christian Marty

Speculation is growing that any modifications to the ageing supersonic airliner might prove too extensive.

Rob Hewson, an aviation expert from Aerospace Analysis and Consulting, said: "The potential for this incident has been laying dormant for 20 years... and it's difficult to see how this can be fixed."

Another aeronautical expert was quoted as saying: "Doubtless it will never fly again."

Last 90 seconds

The crew's first warning that something had gone wrong came from the control tower at Charles de Gaulle airport.

Relatives of the German tourists on board visited the site this week

Shortly after take-off at 1643 local time (1443 GMT) on 25 July, the control tower told the cockpit: "You have flames. You have flames behind you."

Seven seconds after that message, the flight engineer confirmed: "Breakdown eng... breakdown engine two."

"Cut engine two," he said four seconds later.

The supersonic jet tried to gain speed for an emergency landing, but pilot Christian Marty was heard to say: "Too late... no time."

As the crew apparently tried to steer the plane towards the nearby Le Bourget airport, the final words from the plane came from the co-pilot: "Negative, we're trying Le Bourg...".

Communication between the control tower and the plane was then lost.

'Catastrophic consequences'

The BEA confirmed that the investigation remains focused on the burst tyre triggering a chain of events that brought down the plane.

The crew had no way of knowing about the nature of the fire nor any means of fighting it

BEA report

"The 25 July accident shows that the destruction of a tyre, an event that we cannot say will not recur, had catastrophic consequences in a short period of time, preventing the crew from rectifying the situation," the BEA said.

Since the investigation began, there has been speculation that the metal strip found on the runway had caused the tyre to explode.

The 12 remaining Concordes have been grounded

However the report said that the sequence of damage and the links between the various events have not yet been fully established.

The BEA said at least one fuel tank was ruptured in one or more places, resulting in a substantial fuel leak.

This, it says, resulted in a "very violent fire" within a few seconds of the tyre blowout, and thrust being lost in two of the plane's engines.

British and French air safety authorities suspended the plane's airworthiness certificates in August.

The two nations said the 12 remaining Concordes would remain grounded until the risk stemming from tyre blowouts could be addressed.