The Concorde Redemption
Can the superplane make a comeback?
- By Joseph Harriss
- Air & Space magazine, September 2001
(Page 4 of 5)
Last year’s crash shocked the world. Yet the omens had long indicated that not all was well with the beautiful white bird. The very day before the crash, Air France discovered cracks in the wings of four of its six aging Concordes (though not in the one that crashed). This followed British Airways’ finding cracks, like those at Air France, termed non-safety-critical, in all seven of its airplanes; it grounded one for repairs just before July 25.
Perhaps more ominous is the long series of incidents and warnings that came to light as crash investigators and the media delved into Concorde’s past. For example, aircraft belonging to both companies had lost parts of their elevons and rudders several times in flight but were able to land safely. In 1998, the Olympus 593 engines were found to have 152 problems in hardware design or other factors, 55 of which were considered “significant risks,” and BA and Rolls-Royce initiated a plan to remedy them. The engine study warned, “A major technical event would probably end Concorde operation.”
But the scariest scenario to come out this year has been the BEA’s list of 57 tire-related incidents from 1976 to 2000, 30 of which were on Air France flights and 27 on British Airways. Of those, 32 blowouts damaged the aircraft’s structure, engines, or hydraulics, and six resulted in penetration of one or more fuel tanks.
The worst of these occurred on June 14, 1979, when Air France Flight 054 to Paris blew the two rear tires on its left main gear on takeoff from Washington Dulles Airport, hurling high-speed rubber and wheel rim debris at the left wing and engines. The flight crew knew about the blown tires and were diverting to New York, but they were unaware of the true extent of the problem until a passenger convinced the mostly indifferent cabin attendants to bring a crew member back to examine a 12-square-foot hole in the top wing skin. “I took the gentleman who had come back from the flight deck to my seat and virtually held his head to the window so that he could look down and see the hole in the wing,” the passenger wrote in his harrowing statement to the National Transportation Safety Board (available at www.airspacemag.com). “When he saw the hole, he exclaimed, ‘Mon Dieu!’ ” The crew managed an emergency landing at Dulles with Jet A1 streaming from a dozen holes in fuel tanks, damage to the number two engine, severed electrical cables, and the loss of two of three hydraulic systems. Following recommendations from the NTSB, the FAA urgently telegraphed airworthiness directives to both Concorde operators detailing procedures for more intensive checks of tires, wheels, and brakes.
The airplane was later modified to include roll-on wheel rims, strengthened tires, and a tire failure warning in the cockpit. But even after the NTSB’s then-chairman, James B. King, wrote to his French counterpart on November 9, 1981, expressing “serious concern” about “the repetitive nature of these incidents,” they continued. As another former NTSB chief, Jim Burnett, points out, “Concorde could have been certified with a design flaw nobody noticed at the time. If there were as many Concordes flying as 737s, I suspect that we would have seen this kind of accident many times.”
Will the current modifications solve the problem for good? Because EADS Airbus is responsible for the wings, it has taken the lead in trying to find the solution. Its engineers quickly focused on modifications to the fuel tanks to cut the risk of fire from a fuel leak, and armoring electrical cables, which were suspected of igniting the fire with a spark, in the airplane’s wheel wells.
Armoring the wiring was the easy part. It was shaped into “looms” of 15 to 20 cables each, the main one going to the brake cooling fans. These were then protected with braided stainless steel and Teflon, rather than the aluminum tubing used before. To protect the fuel tanks, engineers decided on flexible liners of Viton, a heat-resistant rubberized sealant, and Kevlar, a material used in bulletproof vests. Five times stronger on a weight basis than steel, the thin sheets of Kevlar are sandwiched between layers of Viton. The liners, the reasoning goes, will reduce any shock wave that would be produced by debris and limit the flow of fuel by being sucked down into a hole.
Still, this sort of modification has never been tried before on an airliner. If the theory is simple, the execution is enormously complex. “The liners are actually in the form of 102 shallow trays that go into six fuel tanks, depending on their proximity to the wheels,” explains Claud Freeman, working at the Heathrow hangar on Alpha Foxtrot, the first Concorde to receive the modifications. “Concorde was in effect hand-built, with each one slightly different, so each liner is custom molded to achieve the exact shape and size. We have to keep them separate from the wing skin, because circulating fuel keeps it cool at supersonic flight. That’s why the liners’ sides are attached to some 5,000 separate attachment brackets bolted to wing spars. Because the fuel can’t flow as freely as before, this will create about 880 pounds of additional unusable fuel. We might have to take out a row of seats.”