The jet engine fan blade that broke loose on a United Airlines flight Saturday near Denver, triggering a massive failure leading to the grounding of dozens of Boeing Co. 777s, resulted from metal fatigue, according to National Transportation Safety Board Chairman Robert Sumwalt.
A preliminary examination of fragments found after the episode, which sent metal chunks raining on a suburban neighborhood, suggested a crack that grew gradually over time prompted the failure, Sumwalt said Monday night.
NTSB investigators have begun reviewing maintenance records, interviewing the crew and examining the two crash-proof recorders recovered from the plane, Sumwalt said. They are also reviewing the potential similarity to other failures.