The Federal Aviation Administration issued an Emergency Airworthiness Directive Tuesday night, ordering U.S. airlines to inspect any aircraft with certain Pratt & Whitney PW4000 engines. United Airlines is the only commercial carrier still using that engine, which is mated to Boeing 777s.

In a press release accompanying the directive, the agency said, “The FAA is taking this action as the result of a fan-blade failure that occurred Saturday on a Boeing 777-200 that had just departed from Denver International Airport,” the agency said in a release accompanying the emergency airworthiness directive. “Although the aircraft landed safely, the failure resulted in damage to the engine, an in-flight engine fire, and damage to the airplane.”

It added, “After reviewing the available data and considering other safety factors, the FAA determined that operators must conduct a thermal acoustic image (TAI) inspection of the large titanium fan blades located at the front of each engine. TAI technology can detect cracks on the interior surfaces of the hollow fan blades, or in areas that cannot be seen during a visual inspection.”

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The emergency airworthiness directive noted, “This emergency AD was prompted by the in-flight failure of a 1st-stage low-pressure compressor (LPC) blade on a PW4077 model turbofan engine resulting in an engine fire during flight,” the directive explained. “This condition, if not addressed, could result in 1st-stage LPC blade release, damage to the engine, and damage to the airplane.”

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.

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The FAA 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 following the incident.Airlines in Japan and Korea have also grounded them.

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.

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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.

Contributing: Associated Press

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