Further investigation into the cause of United Airlines Flight 328’s engine failure, which scattered debris over Broomfield last month, confirms “multiple fatigue fracture origins” on a fan blade, according to new findings released Friday, but the probe remains ongoing.
The National Transportation Safety Board released an update and preliminary findings from its investigation into the Feb. 20 flight out of Denver, a Boeing 777 bound for Hawaii with 231 passengers and 10 crew members on board.
Passengers captured video of the crippled engine, wobbling and on fire, as the jet returned to DIA. No one was injured on the plane, or in Broomfield, where debris rained down on a park and in a residential neighborhood.
“The engine fan blade with the fractures consistent with fatigue” has been sent to a metallurgical laboratory at Pratt & Whitney, the engine manufacturer, for further examination, the NTSB said on Friday. The ongoing work at Pratt & Whitney will be led by an NTSB metallurgist.
“Efforts to further characterize the fracture surface, including identifying the primary origin and counting striations, are ongoing,” according to the news release.
Facts gathered to date in the investigation, and provided in the Friday update, include:
- Initial examination of the right engine fire damage found it was primarily contained to the engine’s accessory components, thrust reverser skin and composite honeycomb structure of the inboard and outboard thrust reversers
- The spar valve, which stops fuel flow to the engine when the fire switch is pulled in the cockpit, was found closed — there was no evidence of a fuel-fed fire
- All fan blade roots were in place in the fan hub and two blades were fractured<
- One fan blade was fractured 7.5 inches above the base at the trailing edge, with the fracture surface consistent with fatigue
- The second fractured blade exhibited indications of overload failure, consistent with secondary damage
The blades in question were last inspected in 2016 and data collected in that inspection was reviewed in 2018 after a Feb. 13, 2018, incident involving a Boeing 777 with Pratt & Whitney PW4077 engines, the release said.
“No conclusions regarding the cause of the engine failure should be made based on the information contained in the (Friday) update,” the NTSB said. “The information in the update is preliminary and subject to change as the investigation continues.”
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