first_imgPHILADELPHIA — The investigation into a deadly engine failure on a Southwest jet is focusing on whether wear and tear caused a fan blade to snap off, triggering a catastrophic chain of events that killed a passenger and broke a string of eight years without a fatal accident involving a U.S. airliner.From investigators’ initial findings, the accident appears remarkably similar to a failure on another Southwest plane two years ago — an event that led the engine manufacturer and regulators to push for ultrasonic inspections of fan blades on engines like the one that blew apart at 32,500 feet over Pennsylvania on Tuesday.When investigators from the National Transportation Safety Board examined the broken engine in Philadelphia just hours after it made an emergency landing, they immediately saw that one of the left engine’s 24 fan blades was missing.“This fan blade was broken right at the hub, and our preliminary examination of this was there is evidence of metal fatigue where the blade separated,” said NTSB chairman Robert Sumwalt.Metal fatigue is a weakening of metal from repeated use and involves microscopic cracks. It can occur in fan blades, the aluminum skin on most planes, or other metal parts.last_img

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