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Monday, March 31, 2008

Brake Problems Led to United Jet Skids

Joy Finnegan

From the New York Times:
Two United Airlines A320 jetliners skidded off runways in recent months because of crossed wires in their antilock brakes, the airline said. A United spokeswoman, Megan McCarthy, said on Sunday that both planes had been tested after maintenance, using a test procedure devised by their builder, Airbus. United, owned by the UAL Corporation, is evaluating the test procedure, she said. A spokesman for Airbus, Clay McConnell, said that his company was working with the airline and federal officials to investigation, but had no indication thus far that the test procedure was inadequate when properly carried out. One of the planes, landing at O’Hare International Airport in Chicago on Oct. 9, skidded off the runway and then back on. A passenger and a flight attendant suffered minor injuries. On Feb. 25, a plane landing at Jackson Hole, Wyo., skidded past the end of a runway and hit a snow bank. Passengers and crew used the emergency slides to get out; there was one minor injury. The National Transportation Safety Board is investigating both incidents. The fact that they had the same cause was reported Sunday by The Chicago Tribune. Airplanes have antiskid systems similar to those on cars, though they are more automated. The brakes are applied when there is enough weight on the wheels; if a wheel starts to lock up and skid, the computer releases pressure on it to allow it to turn again. According to a preliminary report on the Jackson Hole accident on the safety board’s Web site, investigators found that, because of crossed wires, the system was using the speed of one wheel to decide to release the pressure on another wheel, almost guaranteeing a skid. A check of United’s other 95 A320s found one additional plane with crossed wires.
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