The Concorde Redemption
Can the superplane make a comeback?
- By Joseph Harriss
- Air & Space magazine, September 2001
(Page 2 of 5)
Two official French inquiries were set in motion. The BEA searched for causes, while a judicial investigation headed by three magistrates tried to determine legal responsibilities. As the investigation dragged on for months, Britain’s Air Accidents Investigation Branch, which participated in the inquiry under terms of a long-standing Franco-British agreement on Concorde safety incidents and was eager to keep the investigation moving, officially protested against “unacceptable procedural delays” in France, to no avail.
The first puzzle to solve was a piece of the number five fuel tank found on the runway that somehow had been torn loose from the inside out. Researchers from European Aeronautic Defense and Space Co. (EADS), successor to the original French Concorde builder, Sud-Aviation, ran a computer simulation that came up with the answer: When a large piece of tire weighing about nine pounds struck the underside of the left wing, the impact generated a shock wave, propagated through the full tank of jet fuel, that moved first up, then down, exploding outward. The resulting one-square-foot hole created a massive kerosene leak—on the order of 20 gallons per second—that somehow ignited.
Why was there such a large chunk of tire, bigger than usual, after a blowout? Investigators found a 17-inch piece of titanium on the runway, a thrust reverser wear strip from an airliner that had taken off minutes before Flight 4590. Striking it at high speed, they theorize, the number two tire was scalped of a five-foot length of tread, which was whipped up at the wing by tremendous centrifugal force, producing the shock wave.
But the most controversial finding concerned a spacer that normally holds two lateral rings in position on the oleo/bogie coupling of the left main gear and is vital to wheel alignment. Apparently because of an Air France maintenance error, the spacer was not reinstalled after routine maintenance work performed four days before the crash, the BEA preliminary report says. Nonetheless, the BEA ruled out the missing spacer as a cause of the crash. (Air France, which sources close to the investigation say has been “traumatized” by the crash, and which was sued for some $100 million by families of the crash victims, declined repeated interview requests for this article.)
“The truth is that because of that missing spacer, the left main gear was slightly skewed on the takeoff roll. Skidding heated and wore down the tire, caused the plane to drift to the left side of the runway, and kept it from accelerating normally,” charges Jean-Marie Chauve, a 37-year Air France veteran and retired Concorde pilot who has done his own calculations—and had them verified by independent experts—based on published information from the flight data and cockpit voice recorders. His version is seconded by Michel Suaud, a longtime Concorde flight engineer who is now retired. They spent several months preparing a detailed report on the crash, which they have presented to the investigating magistrate of the judicial inquiry.
“Our figures show that the plane was moving to the left at the start of the takeoff roll, not just after the blowout and loss of engines one and two,” Chauve says. “The tire burst at around 174 knots and only after the blowout did it strike the metal strip. If acceleration had been nominal, the plane would have been airborne about 50 yards before reaching the strip. The BEA says the leftward yaw was caused by loss of thrust from the left engines, not by the skewed bogie. But they’ve never shown us where our figures are wrong. They are under pressure to make this look like a freak accident caused by that piece of metal on the runway. That would cover up Air France’s fault in letting a plane take off that wasn’t ready.”
Asked about this, BEA chief Paul-Louis Arslanian responded: “It’s true that, due to a regrettable maintenance error, the spacer had not been replaced. But our investigation shows that its absence, though it slightly affected alignment of the left gear, had no influence on the way the tires were worn, or on the plane’s trajectory and acceleration.”
The argument may never be settled to everyone’s satisfaction. Meanwhile, the DGAC and CAA called in the original Concorde builders, BAE Systems, successor to British Aircraft Corporation, and EADS Airbus, along with the original Olympus engine manufacturers, Rolls-Royce and Snecma. If Concorde were to fly again, they would have to keep that kind of accident from happening. (French and British regulations do not require waiting for results of the investigation to begin modifications, or even for the airlines to resume service.) Says Gérard Le Houx, a DGAC official in Paris: “We told them there are three general problem areas: reinforcing the plane’s structure, mainly the fuel tanks, preventing such a fire, and ensuring the engines are not affected by fire when there’s a fuel leak. Once they give us those solutions, we can consider restoring Concorde’s certificate.”