David Learmount/LONDON Julian Moxon/PARIS
Vital new information on what happened to the Air France Aerospatiale/British Aerospace Concorde when it crashed just after take-off from Paris Charles de Gaulle airport has increased the likelihood that the aircraft will fly commercially again.
A second interim report by the French Bureau Enquetes-Accidents (BEA) confirms that the wing fuel tank was not pierced from outside, and the fierce underwing fire resulting from the fuel leak may well have been ignited by a flashback from the engine reheat, not as originally thought by damaged electrics on the landing gear or in the undercarriage bay. It is believed that fire could have travelled forwards in the boundary layer eddies just under the wing.
BEA director Paul-Louis Arslanian says that, although the full report "is far from finished", enough data will soon be available to enable the authorities to approve aircraft modifications enabling the return of Concorde's certificates of airworthiness.
Originally, it had been thought the massive underwing fuel leak in the fatal 25 July 2000 accident was caused by a piece of rubber from a main gear tyre explosion which pierced the tank from outside. The BEA now confirms that shock waves in the fuel itself and ripples propagating in the tank's external skin caused by the impact of a 4.5kg (10lb) lump of tyre carcass punched out a piece of tank/lower wing skin which was found on the runway after the accident.
Engines 1 and 2 were producing no thrust at impact. Although both had received some "soft body damage" it was not enough to make them fail, the report says. The crew had shut down No 2, which had given a false engine fire warning, but No 1 engine probably lost some power with the ingestion of fuel and hot gases from the underwing conflagration. Finally engines 3 and 4 failed because of "the distortion of the airflow entering the intakes" as the Concorde reached an angle of attack above 25° and a left roll rate of 100°/s shortly before crashing.
A series of ballistic tests will be carried out to validate modifications to the fuel tanks, which centre on Kevlar-based liners designed to prevent significant fuel leakage in the event of tank rupture.
Further modifications include electrical isolation of the 115V wheel brake fan system during take-off, and physical protection of electrical systems around the landing gear. An Air France Concorde will undergo taxi trials to establish how the piece of metal on the runway from a Continental DC-10 cut into the tyre, causing it to explode.
The report also shows how a spacer on the affected undercarriage which holds two lateral rings in position was missing from the oleo/bogey coupling. This retainer was not replaced after maintenance carried out a week before the accident, says the report, but it does not venture a possible connection with the accident cause.
Source: Flight International
