WASHINGTON (Reuters) – The damage to the blade of an engine that failed on a United Airlines Boeing 777 flight is consistent with metal fatigue, based on a preliminary assessment, the president of the US air accident investigator said on Monday.
The Pratt & Whitney PW4000 engine failed on Saturday with a “powerful explosion” four minutes after taking off from Denver, National Transportation Safety Board (NTSB) chairman Robert Sumwalt told reporters following an initial analysis of the flight data recorder and the voice recorder in the cab.
He said it remained unclear whether the incident was consistent with an engine failure on another United flight to Hawaii in February 2018, which was attributed to a fatigue fracture in a fan blade.
“What is important is to really understand the facts, circumstances and conditions surrounding this particular event before we can compare it to any other event,” Sumwalt said.
The engine that failed on the 26-year-old Boeing Co 777 and threw parts over a Denver suburb was a PW4000 used on 128 aircraft, or less than 10% of the global fleet of more than 1,600 aircraft delivered. 777 wide planes.
In another incident on Japan Airlines (JAL) 777 with a PW4000 engine in December 2020, the Transportation Safety Board of Japan reported finding two damaged fan blades, one with a metal fatigue crack. An investigation is ongoing.
The focus is more on engine maker Pratt & Whitney, and analysts expect a low financial impact on Boeing, but the PW4000’s problems are a fresh headache for the planner as it recovers from the much worse 737 MAX crisis. Boeing’s narrow-wing pilot was grounded for nearly two years after two fatal crashes.
The United engine fan blade will be examined on Tuesday after being transported to a Pratt & Whitney lab where it will be examined under the supervision of NTSB investigators.
The US Federal Aviation Administration (FAA) said on Monday that it had already assessed whether inspections of the fan blades were adjusted following the December incident in Japan, after reviewing maintenance records and conducting a metallurgical examination of the fan blade fragment.
Boeing recommended that airlines suspend the use of aircraft while the FAA identified an appropriate inspection protocol, and Japan imposed a temporary suspension of flights.
The FAA intends to issue an emergency airworthiness directive soon that requires intensified inspections of the fan blades for fatigue.
The FAA in March 2019, after the failure of the United engine in February 2018, attributed to the fatigue of the fan blades, ordered inspections every 6,500 cycles. A cycle is a single takeoff and landing.
Sumwalt said the United incident was not considered a continuous engine failure because the insulation ring contained parts while flying.
He said there was minor damage to the aircraft body, but there was no structural damage.
The NTSB will look into why the engine body separated from the plane and also why there was a fire, despite indications that the engine fuel has been stopped, Sumwalt added.
Pratt & Whitney, owned by Raytheon Technologies Corp., said Sunday that it is coordinating with regulators to review inspection protocols.
Nearly half of the global fleet of Boeing 777s equipped with PW4000s operated by airlines, including United, JAL, ANA Holdings, Korean Air and Asiana Airlines, have already been based on a decline in travel demand due to the coronavirus pandemic.
Reporting by David Shepardson in Washington and Jamie Freed in Sydney; additional reporting by Tracy Rucinski in Chicago; Editing by Kim Coghill and Gerry Doyle