Concorde grounding could last several months

Concorde's suspension from flying will last months, and possibly forever, as parts manufacturers and aviation experts ponder the form and cost of design changes necessary to make it safe.

Concorde's suspension from flying will last months, and possibly forever, as parts manufacturers and aviation experts ponder the form and cost of design changes necessary to make it safe.

The Civil Aviation Authority (CAA) officially withdrew the supersonic aircraft's airworthiness certificate yesterday morning, three weeks after the crash of an Air France Concorde on 25 July.

It followed the findings of French, British and German investigators that the Paris crash was principally caused by pieces from a burst tyre puncturing the fuel tanks. British Airways cancelled all bookings for its seven planes until September.

The CAA defended its decision not to ground all the Concorde fleet immediately after the crash. "We require technical grounds that affect the whole fleet of aircraft beforewe ground them," said Mike Bell, of the CAA's safety regulation group.

Burst tyres are comparatively common on aircraft - and especially Concorde, which takes off between 20 and 25 per cent faster than conventional aircraft. It also has thinner metal covering the underside of the fuel tanks, making them easier to puncture.

Ken Smart, head of the government's Air Accident Investigation Board, said there have been seven incidents previously where Concorde tyres have burst and the fuel tanks had been punctured - but in those it was always metal fragments which caused the damage. In each case modifications were made to prevent a repetition of the particular circumstance. The July 25 accident was the first crash involving the supersonic plane.

A system to prevent fragments of burst tyre puncturing the fuel tanks will require "innovative" design never seen on airliners before, experts said. With a price tag sure to top millions of pounds, it could also cost too much to be commercially sensible on the 25-year-old aircraft.

One possibility would be to strengthen the tyres, made by Goodyear and Dunlop, said Kieran Daly, editor of the aviation website Air Transport Intelligence. "The other possible solution is strengthening the structure around the fuel tank, but that would have a very serious weight penalty," he said. "It would also take a considerable time to devise that fix and get it on the aircraft -- months or more. The most practical idea may be devising some sort of casing around the tyres, a shield. This would also add extra weight to the plane and I can't think of an aircraft that you find such a structure."

Chris Yates, Jane's Aviation security editor, said a "tyre-shield" might have to be made of titanium, to combine strength and lightness. But that would be too expensive for an aircraft with a maximum of 15 years' service remaining.

Mr Daly said: "It has also been suggested that Concorde could fly with the wing fuel tanks empty. However, the plane already has a very tight amount of spare fuel on its Atlantic routes."

The CAA said it had been surprised that the investigation had determined that the tyre debris alone had caused the crash, and that this was the reason for withdrawing certification.

"That has never happened on another aircraft," said Mr Smart. "The damage caused by the tyre burst led to one or more major ruptures of the fuel tank, hydraulic systems, damage to both engines' which caused them to lose power during the plane's short flight.

"It is a requirement of airworthiness that tyre debris alone should not be able to have such a catastrophic effect," he said.