Investigators say tire debris may have ruptured Concorde fuel tank

Tires lie amid the wreckage of Concorde Flight 4590

In this story: Reinforced rubber Warning light RELATED STORIES, SITES

LONDON (CNN) -- The investigation into the crash of Air France Concorde Flight 4509 is increasingly focusing on the aircraft's tires, with experts saying debris from a blowout on the left-hand side of the plane could have ruptured a fuel tank in the aircraft's wing.

Concorde has suffered a succession of tire blowouts since it started operating commercially in 1976.

The high speed at which the aircraft takes off and lands -- 250 mph -- means that the damage caused by blowouts can potentially be more severe than that on normal planes.

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In 1979, two tires on an Air France Concorde exploded as it was taking off from Dulles Airport in Washington, damaging the plane's No. 2 engine, rupturing three fuel tanks, and damaging hydraulic cables and fuel wires.

There are reported to have been at least six further serious tire failures on Air France Concordes. In the same period, there have been 12 tire blowouts on British Airways Concordes, although only two were classified as dangerous.

Reinforced rubber

Each Concorde has eight main wheels and two nose wheels. Air France Concordes use American-made Goodyear tires. British Airways Concordes use British-made Dunlop tires.

The tires are made from specially reinforced rubber and nylon, and measure 47 inches (119 centimeters) in diameter by 15.75 inches (40 centimeters) in width. The nose wheels are each 31 inches (78 centimeters) by 10.75 inches (27 centimeters).

They are attached to the alloy wheel-rim with high-tensile steel wire, and inflated with nitrogen to 183 pounds per square inch, roughly six times the pressure of the average car tire.

Nitrogen is used rather than air because it ensures a stable pressure under extreme conditions.

Warning light

A red warning light has been installed in Concorde cockpits to alert the pilot to any tire problems during takeoff. The light is only activated if the aircraft is traveling at less than 150 mph, however. Any faster than that and the plane cannot stop, and so the light remains off.

Jean-Paul Villeneuve, of France's air accident investigation bureau, the Bureau Enquete Accident, said: "The tires are just one of many elements we are investigating. We have, however, found fragments of rubber and metal from one or possibly two of the aircraft's tires on and around the runway at Charles de Gaulle. This would suggest that there was some sort of blowout prior to takeoff."

Dick Downs, editor of Avionics Magazine and a former pilot, said: "It's certainly possible that a blowout could have been the cause of the tragedy. It's important not to be alarmist, however, and imagine there's some inherent design fault in Concorde's tires.

"It has had blowouts before, but then so have all planes. Twenty-odd incidents in 20 years doesn't strike me as a particularly high total, especially for a high-performance aircraft like that."

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