Staff who carried out engine work are interviewed

The Inquiry

Air France Concordes might resume flying within days, the French transport minister Jean-Claude Gayssot said yesterday, and an analysis of data from the doomed Concorde's black box might be available by this evening, he added.

Air France Concordes might resume flying within days, the French transport minister Jean-Claude Gayssot said yesterday, and an analysis of data from the doomed Concorde's black box might be available by this evening, he added.

French and British investigators seeking the cause of the crash have interviewed ground staff who replaced the reverse thruster, minutes before takeoff, on one of the engines which caught fire.

Air France officials said the pilot, Captain Christian Marty, had ordered a new part fitted on the No2 engine on the left wing, in a 30-minute operation.

"I cannot exclude the possibility of asking for a new certification of the Concorde engines," Mr Gayssot said. But the future of the supersonic jet, he added, was "not in question".

Aviation experts are increasingly certain there was a massive "uncontained" engine failure which affected not only the damaged propulsion unit but the control systems needed to pilot the plane safely.

When the Concorde arrived in Paris from New York on Monday, No2 engine's reverse thruster - a clamshell-like pair of cowlings which close over the jet exhaust to redirect the thrust forward, so slowing it on landing - was not working.

Although no spare part was available directly, and the manufacturers, Rolls-Royce of Britain and Snecma of France said the plane could safely fly in that condition, Captain Marty ordered the replacement.

The part was taken from a backup Concorde and installed in a 30-minute procedure, Air France said yesterday. But it is unclear how the reverse thruster, at the back of the engine, could have caused the catastrophic failure. Ground control reported seeing huge flames coming from the aircraft just 56 seconds after takeoff.

Captain Marty radioed the control tower that he had a failure in No2 engine, could not stop the flight and was going to try to head for Le Bouget airport, six miles away. But he was unable to control the stricken 185-tonne aircraft.

The cause of the huge plume of flame remains a mystery so far, but a dramatic failure inside the engine seemed most likely. Inside their cylindrical casing, jet engines are made up of rows of propeller-like turbine blades racing at high speed. If blades break off - perhaps if a bird is sucked into the engine or in the unlikely event of metal failure - they fly out into the casing with enormous velocity.

The casing is supposed to contain the blades to prevent damage to the rest of the plane, but there have been instances of so-called uncontained failure. If another engine is next to one that explodes, as on a Concorde, then it too might be knocked out. Depending on the plane's design, the flying pieces might hit other vital systems, such as navigation equipment.

Malcolm English, editor of the leading industry monthly Air International, said a pilot's first instinct if they lose engine power is to keep the plane flying and avoid "stalling" - when the plane loses all forward momentum - even if they cannot avoid losing height, while they look for the best available landing site.

"In the case of a Concorde, I haven't got a clue how you would expect to do that," he added. Mr English also said fire could rob the pilot of control of the aircraft. "The (control) rods can burn through, if there is a very intense fire."

In that case, the plane might pitch uncontrollably and stall, as witnesses said the Air France Concorde did.

At the Farnborough Air show yesterday, aeronautical engineers were reluctant to comment, though one who asked not to be named pointed to the large flame in the photograph taken just before the crash.

The engine failure may have started a fuel tank fire which, in turn, downed the plane, he said. Concorde's fuel tanks are embedded in the wings. "To me, that looked too big to be just an engine fire." the engineer said.

Concorde is the only commercial jetliner to use afterburners, which provide extra thrust on takeoff. Afterburners, used by high-performance fighters, mix warm air and fuel in the tailpipe of the engine.

Andre Turcat, the pilot who flew the first test flight of the Concorde in 1969, said he believed the cause of the accident was "much more serious" than just a malfunctioning engine. He said mere engine failure could not have caused the plane to go down.

Another former Concorde pilot, Germain Chambort, said the aircraft would become uncontrollable if it lost both engines on one side, a possibility since the Concorde's Rolls-Royce Snecma Olympus turbojets are mounted in pairs. "Failure of both engines at low speed just after takeoff is impossible to control."

William Waldock of the Center for Aerospace Safety Education at Embry-Riddle Aeronautical University, agreed with that

"For any airplane, the absolute worst time you can have something come unstuck is after takeoff."

But some experts pointed out that the design of Concorde would not be copied today, because putting the engines in pairs increases the risks of a failure.

David Brister, a former Concorde pilot who flew the aircraft from 1976 to 1982, said: "Concorde is unusual in that the two engines on each wing are very close together.

"Any four-engined aircraft can cope perfectly well with losing one engine, but if two go on the same side you can be in for a difficult time."

With Concorde, he said, "the engines are so close that it is possible one could affect the other, and then you have a much more serious situation".