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WASHINGTON – The chief of the National Transportation Safety Board said on Monday that damage to a fan blade of a failed Pratt & Whitney engine on a United Airlines Boeing 777-200 is consistent with metal fatigue, according to an assessment preliminary.

At a press briefing, NTSB Chairman Robert Sumwalt said it was not clear whether the failure of the PW4000 engine with a “loud bang” four minutes after takeoff on Saturday was consistent with a failure of engine on another United flight to Hawaii in February 2018, which was attributed to a stress fracture in a fan blade.

The engine that failed on the 26-year-old Boeing 777, losing parts over a suburb of Denver, was a PW4000 used on less than 10% of the world’s 777 widebody jet fleet.

Japan’s Transportation Safety Board reported that it found two damaged fan blades, one with a metal fatigue crack, in another incident in December on Japan Airlines 777 with a PW4000 engine. The investigation is continuing.

The focus is more on engine maker Pratt & Whitney, and analysts expect little financial impact on Boeing, but the PW4000 issues are another headache for the aircraft manufacturer as it grows. is recovering from the much more serious crisis of the 737 MAX. Boeing’s flagship narrow-body aircraft was grounded for nearly two years after two fatal crashes.

The United motor’s fan blade was scheduled for examination on Tuesday after being transported to a Pratt & Whitney lab, where it will be examined under the supervision of NTSB investigators.

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

Boeing has recommended airlines suspend aircraft use while the Federal Aviation Administration identifies an appropriate inspection protocol, and Japan has suspended those flights.

The FAA plans to issue an Emergency Airworthiness Directive soon that will require intensified fan blade inspections for fatigue.

In March 2019, after the February 2018 United engine failure attributed to fan blade fatigue, the FAA ordered inspections every 6,500 cycles. A cycle is a takeoff and a landing.

Sumwalt said the United incident was not considered an unconfined engine failure because the containment ring contained the parts as they flew away. There was minor damage to the plane’s body, but no structural damage, he said.

The NTSB will investigate why the engine cowl separated from the plane and why there was a fire despite reports that the engine’s fuel had been cut, he said.

Pratt & Whitney, which is owned by Raytheon Technologies Corp., said Sunday it was coordinating with regulators to review inspection protocols.

Nearly half of the global fleet of 128 planes operated by United, Japan Airlines, ANA Holdings, Korean Air, Asiana Airlines and other airlines had already been tied up in a drop in travel demand due to the pandemic of coronavirus.

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