(NBC News) National Transportation Safety Board investigators charged with finding out what caused a Southwest Airlines jet engine to break apart in mid-air Tuesday are focusing on whether wear and tear caused a fan blade to break off.
"There is evidence of metal fatigue where the blade separated," says NTSB Chairman Robert Sumwalt.
Officials discovered plane debris in a rural area in eastern Pennsylvania.
The Boeing 737 was at 32,000 feet when the left engine exploded about 20 minutes after takeoff. Shrapnel from the engine struck the plane and shattered a window causing the cabin to de-pressurize.
Killed in the accident was 43-year-old bank executive Jennifer Riordan of New Mexico, who was partially sucked through the window before passengers were able to pull her back inside.
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