Debris on runway linked to fatal Concorde crash

A 16-inch piece of metal slashed a tire, sending fragments into fuel tanks.

©Washington Post

© St. Petersburg Times, published August 11, 2000

PARIS -- A 16-inch piece of metal lying unnoticed on the runway used by the Air France Concorde that crashed last month appears to have set in motion a chain of events that quickly brought the plane down in a blaze of burning fuel, French investigators said Thursday.

The metal strip apparently slashed into a tire as the Concorde neared takeoff speed July 25 at Paris' Charles de Gaulle Airport. The tire burst, sending fragments ramming through one or more of the seven fuel tanks in the supersonic plane's left wing, investigators said.

That resulted in "very considerable leakage of fuel" and fire, investigators said. The crippled jet trailed flames spectacularly as it crashed just beyond the airport, killing 109 people on the plane and four on the ground.

The Transport Ministry's Accident and Inquiry Office said that it hadn't yet determined where the piece of metal came from but that it matched the profile of a cut in the ruined tire. Much work needs to be done before the investigation is complete, it said, noting that the exact sequence of damage that the fragments caused to the plane remains unclear.

The communique did not address what exactly brought the plane down -- the fire or some other damage. Flight data recorders show that one of the plane's four engines failed and another lost power, indicating the plane suffered damage other than punctured fuel tanks, possibly ingestion of debris by the engines.

Problems with blown Concorde tires have been reported since the first of the supersonic jets flew in 1969. The Concorde lands and takes off at higher speeds than subsonic planes, placing the 47-inch-diameter tires under extreme stress and making any blowout a potential explosion that can damage engines and other nearby structures such as fuel tanks. Blown tires on subsonic planes can cause damage but generally don't have enough energy to be a serious danger.

The accident office said the Concorde was moving at about 195 mph when the tire burst. Concorde takeoff speed is about 220 mph.

Peter Duffey, one of the original eight British Concorde pilots, noted in his 1999 book Comets and Concordes that takeoff speed at maximum weight "is near to the maximum which the tread carcass can stand. Should the aircraft be allowed to overspeed on the runway, one or more of the tires may be "cooked,' weakening them for subsequent takeoffs."

Duffey said he once was landing when a tire burst, disabling the plane's hydraulic systems. He didn't know the bleed-off of hydraulic fluid had left him with no brakes until, while the plane was taxiing, an alert maintenance man saw a trail of fluid, ran out onto the taxiway to wave him down and signaled he should coast to a stop, he said.

"We were within a few moments of making a very sharp-nosed entrance past the gate right into the main terminal building," he wrote. Without brakes, the plane might have hit the building.

The investigators' findings also raise an issue that requires constant vigilance by airports and airlines: "foreign object debris," usually called FOD. Runways are regularly inspected for foreign objects, and waste cans marked "FOD" are often placed near airport gates and in shops so employees can toss in anything that could damage a tire, be picked up by an engine or even cause people to trip. In some airports and shops, airlines have promoted anti-FOD campaigns with posters and bulletins.

The French communique Thursday didn't describe the object found on the Paris runway, calling it only a "piece of metal." In other communiques, investigators described it as a 16-inch strip of metal that did not come from the Concorde.

"After comparison with the profile of the cut in a tire that was destroyed at the start of the accident, it is probable that the piece is at the origin of the cut in the tire," the communique said. "Expert analysis will attempt to confirm this point definitively. Determination of the origin of the (metal) piece is still under way.

"The bursting of the tire caused the projection, at a moment the aircraft was moving at high speed (around 170 knots), of large fragments (more than four kilograms for the heaviest) and with high energy.

"In a process that remains to be determined, damage was then caused very rapidly, to one or several left-side fuel tanks causing a very considerable leakage of fuel and fire. The piece of fuel tank that was found on the runway has been identified as coming from tank No. 5."

The communique noted that each of the large, delta-shaped wings of the Concorde has seven tanks. Tank No. 5 is almost directly over the left landing gear, stretching slightly forward and to the left of the gear.

Although the communique did not say so, it is significant that the tank is in front of the left wing's two engines. Any spray of fuel would tend to be ignited as it flowed back through the flame produced by the afterburners that give the engines extra thrust on takeoff.

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