Federal safety officials are updating their investigation into the engine failure on a United Airlines plane that sent parts of the engine housing raining down on Denver-area neighborhoods last month.
The National Transportation Safety Board said Friday that a microscopic exam confirmed that a fan blade that snapped off had telltale signs of fatigue — tiny cracks caused by wear and tear.
The safety board says the Pratt & Whitney PW4077 engine had been used on 2,979 flights since its last inspection.
After the Feb. 22 incident, the Federal Aviation Administration ordered that certain blades on the same model of engine be inspected for cracks before their next flight.
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The United Airlines Boeing 777, United Flight 328, made an emergency landing at Denver International Airport. Nobody was hurt in the incident. Several large pieces of the plane dropped in Broomfield. Authorities asked residents to call if they found a large piece of the engine.