Federal investigators have revealed that a damaged fan blade was the most likely cause of the engine fire on United Airlines flight 328 from Denver.

The engine failed just four minutes into the Saturday flight from Denver to Hawaii. The incident and subsequent investigation have led to the grounding of more than 100 Boeing 777s. Investigators believe that wear and tear may have caused a fan blade to fracture and break off the Pratt & Whitney engine.

National Transportation Safety Board (NTSB) chairman Robert Sumwalt said that the broken blade chipped off half of a second blade which lead to multiple pieces of debris falling to the ground in surburban areas of Denver. A “loud bang” was heard by both passengers and residents who reported the incident and resulting debris to police. Preliminary assessment by investigators showed that the damage to the fan blade was consistent with metal fatigue.

Sumwalt added that despite the dramatic nature of the incident, there was only minor damage to the aircraft body and no structural damage. There were no injuries on board the plane or to residents on the ground caused by falling debris. he aircraft returned safely to Denver International Airport shortly after the engine fire.

Debris taken to P&W laboratories

The debris has been recovered and has been taken to a Pratt & Whitney laboratory for an examination supervised by NTSB investigators. Investigators will also be studying the aircraft’s maintenance logs and pre-flight safety inspections.

More than 100 Boeing 777s which use the same Pratt & Whitney 4000 engines as the United Airlines flight have been grounded while the Federal Aviation Administration (FAA) investigates the engine blades.

Japanese safety regulators have also banned 777s using the same engine following a problem reported in December 2020. Both ANA and JAL use Boeing 777s with the same Pratt & Whitney engine.

NTSB inquiries can take up to a year to complete and Sumwalt added: “Our mission is to understand not only what happened but why it happened, so that we can keep it from happening again.”


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