Damage to United Boeing 777 engine consistent with metal fatigue: NTSB

By Shepardson David and Released Jamie

WASHINGTON (Reuters) – According to the preliminary evaluation, the Chairman of the U.S. Air Crash Investigator said on Wednesday, Damage to a fan blade on a faulty moteur on United Airlines Boeing 777 is consistent with metal fatigue.

On Saturday, four minutes after the take-off from Denver, the Pratt & Whitney engine PW4000 failed, Chairman of NTSB, Mr Robert Sumwalt, told reporters after an initial review of the flight data recorder and the voice recorder in the cockpit.

The aircraft body sustained minor damage, but no structural damage, he added.

He said it was uncertain if the incident corresponded to a fatigue crack in a fan-blade on a recent Hawaiian United flight in February 2018.

"What is important that we really truly understand the facts, circumstances and conditions around this particular event before we can compare it to any other event," said Sumwalt.

The engine that exploded on the 26-year-old Boeing Co 777, which lost pieces into a suburb of Denver, consisted of a PW4000 on 128 aircraft, or less than 10 percent of the world's fleet of over 1,600 wide-scale planes.

The Japan Transport Safety Board announced that, in a further incident involving Japan Airlines (JAL) 777 with a PW4000 engine during December 2020, two broken fan blades were discovered, one with a metal fracture.

An inquiry is underway.

The emphasis is more on engine manufacturer Pratt and analysts foresee little financial impact on Boeing, but the PW4000 challenge represents a fresh headache for the operator, as it recovers from the much tougher 737 MAX crisis.

After two deadly accidents, Boeing's narrowbody jet was created almost two years ago.

Tuesday, after flying into a Pratt laboratory, the United Engine's fan blade will be examined under the supervision of NTSB investigators.

The US Federal Aviation Administrative (FAA) reported on Monday that, after a maintenance check and a metallurgical review of the fan blade fragment in Japan, it already assessed whether fan blade inspections had to be changed.

Boeing indicated that airlines suspend their use of aircraft because the FAA has established a related inspection procedure and Japan has placed a temporary suspension on flights.

In an FAA evaluation proposal, Pratt & Whitney, which is operated by Raytheon Technology Corp., has proposed that airlines raise inspections, sources with knowledge of the matter said.

Pratt did not immediately respond to a comment message.

The FAA has stated that it aims soon to issue a directive on emergency airworthiness which will include stepped checks of the fan blades for fatigue.

"United Airlines has grounded all of the affected airplanes with these engines, and I understand the FAA is also working very quickly as well as Pratt & Whitney has reiterated or revised a service bulletin," said Sumwalt.

"It looks like action is being taken."

In March 2019, after the fault of the fan blade in the United Engine 2018, the FAA ordered inspections every 6,500 cycles.

A loop is a single start and landing.

The Transport Ministry of South Korea said on Tuesday that it had instructed its airlines to check the fan blades after 1,000 cycles citing Pratt's advice after the United States incident.

Sumwalt said the incident at the United was not deemed an uncontained engine failure because the ring housed the components when they were flying out.

NTSB will look at why the cowling of the engine has detached from the aircraft and why a fire has arisen even when fuel is shut off from the engine, Sumwalt said.

Industry sources said that although Pratt produces the engine, Boeing manufactures the cowling or casing.

On the part of the NTSB, Boeing referred questions.

About half of the global fleet of airlines flying the Boeing 777 PW4000, including United, JAL, ANA Holdings, Korean Air and Asiana Airlines, have already grounded in travel market because of the coronavirus pandemic.

(David Shepardson's reports in Washington and Jamie Freed in Sydney; Tracy Rucinski's reports in Chicago, Joyce Lee in Seoul and Tim Hepher's reports in Paris; Kim Coghill and Gerry Doyle's reports)