By The Associated Press

Boeing has recommended that airlines ground all 777s with the type of engine that blew apart after takeoff from Denver this past weekend, and most carriers that fly those planes said they would temporarily pull them from service.

The U.S. Federal Aviation Administration ordered United Airlines to step up inspections of the aircraft after one of its flights made an emergency landing at Denver International Airport on Saturday as pieces of the engine’s casing rained on suburban neighborhoods. None of the 231 passengers or 10 crew were hurt, and the flight landed safely, authorities said. United is among the carriers that has grounded the planes.

FAA Administrator Steve Dickson identified the focus on the stepped-up inspections as hollow fan blades unique to the Pratt & Whitney PW4000 engine model and used solely on Boeing 777s. Dickson’s statement said the conclusion was based on an initial review of safety data and would likely mean grounding some planes.

Robert Sumwalt, chairman of the National Transportation Safety Board, said during a virtual news conference Monday night that a fractured fan blade found in the engine had visible signs of “damage consistent with metal fatigue.” The broken blade hit and fractured the blade next to it as the engine broke apart, according to a preliminary investigation.

Sumwalt said the blade that fractured first was being flown on a private jet to Pratt & Whitney’s headquarters Monday night to be examined under the supervision of NTSB investigators.

“Our mission is to understand not only what happened, but why it happened, so that we can keep it from happening again,” he said.

Boeing said there were 69 777s with the Pratt & Whitney 4000-112 engines in service and another 59 in storage and affirmed they should be grounded until the FAA sets up an inspection regime.

United had 24 of the planes in service; it is the only U.S. airline with the engine in its fleet, according to the FAA.

Two Japanese airlines have another 32. Japan ordered the planes out of service, according to the financial newspaper Nikkei, while noting that an engine in the same family had trouble in December.

In South Korea, Asiana Airlines grounded nine, seven of which were in service, and Korean Air said it grounded 16 aircraft, six of which are in service.

“We are working with these regulators as they take actions while these planes are on the ground and further inspections are conducted by Pratt & Whitney,” Boeing said in a statement, referring to American and Japanese regulators.

The engine maker said it was sending a team to work with investigators.

The emergency landing this past weekend is the latest trouble for Boeing, which saw its 737 Max planes grounded for more than a year after two deadly crashes in 2019 and is suffering amid the huge reduction in air travel due to the coronavirus pandemic. The Max planes began returning to the skies late last year — a huge boost for the aircraft maker, which lost billions during the grounding because it has been unable to deliver new planes to customers.

Video posted on Twitter from Saturday’s emergency showed the engine fully engulfed in flames as the plane flew. Freeze frames from different video taken by a passenger sitting slightly in front of the engine and also posted on Twitter appeared to show a broken fan blade in the engine.

Passengers, who were headed to Honolulu, said they feared the plane would crash after an explosion and flash of light, while people on the ground saw huge chunks of the aircraft pour down, just missing one home and crushing a truck. The explosion, visible from the ground, left a trail of black smoke in the sky.

United says it will work closely with the FAA and the NTSB “to determine any additional steps that are needed to ensure these aircraft meet our rigorous safety standards and can return to service.”

The NTSB said the cockpit voice recorder and flight data recorder were transported to its lab in Washington so the data can be analyzed. NTSB investigations can take up to a year or longer, although in major cases the agency generally releases some investigative material midway through the process.

Japan’s Ministry of Land, Infrastructure, Transport and Tourism said an engine in the PW4000 family suffered trouble on a Japan Airlines 777 flying to Tokyo from Naha on Dec. 4. The airline has said the plane had engine trouble after takeoff and returned to Naha. An inspection showed damage to the engine case and missing fan blades, according to the airline. Stricter inspections were ordered in response.

Japan Airlines and All Nippon Airways will stop operating a combined 32 planes with that engine, Nikkei reported. ———

This story has been updated to correct the name of one of the Japanese airlines mentioned. It is Japan Airlines, not Japan Airways.

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