Metal fatigue in the fan blades may have been the cause of the engine failure of a Boeing jet in Denver over the weekend, the US National Transportation Safety Board said.
The Pratt & Whitney engine caught fire just after a United Airlines Boeing 777-200 took off during a flight from Denver to Honolulu, with 231 passengers and 10 crew members on board. The pilots made a distress call and returned to Denver.
The next day, dozens of 777 planes were landed after Boeing said those with Pratt & Whitney PW4000 engines should not be used until full inspections could be carried out.
National Transportation Safety Board (NTSB) President Robert Sumwalt said on Monday that a preliminary assessment suggested that the damage was consistent with metal fatigue and that the blade would be examined on Tuesday in a Pratt & Whitney laboratory. under the supervision of NTSB researchers.
Sumwalt said it is not clear whether the PW4000 engine failure on Saturday was consistent with another engine failure on another United flight bound for Hawaii in February 2018, which was attributed to a fatigue fracture in the fan blade.
“The important thing is that we really understand the facts, circumstances and conditions surrounding this particular event before we can compare it to any other event,” said Sumwalt.
In another incident with the same engine type on a Japan Airlines 777 in December 2020, the Japan Transport Safety Council reported finding two damaged fan blades, one with a fatigue metal crack.
The Federal Aviation Administration (FAA) planned to issue an emergency airworthiness directive soon, which will require intensified inspections of the fan blades to check for fatigue.
After United’s engine failure in February 2018 was attributed to fan blade fatigue, the FAA ordered inspections every 6,500 cycles.
Sumwalt said the United incident was not considered to be an unrecognized engine failure because the retaining ring contained the flying parts. There was little damage to the aircraft body, but no structural damage, he said.
The NTSB will investigate why the engine’s fairing detached from the plane and also why there was a fire despite indications that the engine’s fuel was turned off, Sumwalt added.