Dozens of Boeing 777 widebody aircraft have been grounded across the world after an engine failure on a United Airlines flight caused the plane to shed debris across a Denver suburb. 

The US Federal Aviation Administration on Sunday ordered inspections of Boeing 777 planes with Pratt & Whitney PW4000-112 turbines after an uncontained engine failure resulted in an emergency landing of a United flight on Saturday.

The regulator pinpointed issues with the hollow fan blades that were “unique to this engine”.

United flight 328 had to return to Denver airport shortly after take-off on Saturday after debris, including parts of the cowling that were designed to contain the engine, fell from the aircraft towards the ground.

United said it was voluntarily and temporarily removing its 24 active Boeing 777 aircraft powered by the same model of engine and working with regulators to ensure they could return to service. The airline has 28 of these jets in storage. 

Japan’s ministry of transport on Sunday ordered domestic airlines to ground planes with those engines until the US incident was investigated.

South Korea’s two biggest carriers, Korean Air and Asiana Airlines, have also said they would ground the jets, according to Yonhap news agency.

In a separate incident at the weekend, a Boeing 747 cargo aircraft powered by a smaller version of the engine was forced to turn back after parts of the engine dropped off shortly after take-off from Maastricht in the Netherlands. It is not clear whether the two incidents are related. No one was injured in either case.

The incidents are yet another blow to Boeing, which is still reeling from the 18-month grounding of its 737 Max aircraft as well as the impact of the pandemic on demand for its planes. It posted a record loss in 2020. Two 737 Max crashes in October 2018 and March 2019 killed 346 people.

The US lifted a grounding order on those jets late last year, while the EU cleared the planes in January. 

Uncontained engine failures — where the engine’s casing fails to prevent debris from being ejected at high speeds in all directions, potentially threatening the integrity of the aircraft itself — are particularly serious, but not unheard of, said John Strickland, of aviation consultancy JLS Consulting.

This debris from the United Airlines flight 328 engine fell on a yard in Broomfield, Colorado © Broomfield Police Department/AFP

The PW4000 turbine involved in the incident and the 777 aircraft had both flown safely for decades, and investigators would have to determine whether the incident was due to age or some other factor, he said.

The particular variant of aircraft powered by the Pratt & Whitney engines was not widely used. Cirium, the aircraft data consultancy, estimates there are just 60 777 aircraft in service with the PW4000 engines, and a further 67 in storage. The biggest customers after United are Japanese and Korean airlines.

“This version of the 777 is out of production, so there is no impact for Boeing,” said Rob Stallard, an analyst at Vertical Research. “The current version of the 777, which has also only got a few years left in production, only uses the GE-90 engine.

Boeing said it was “actively monitoring recent events” and was working with the regulators in the US and Japan. It recommended suspending the operations of all its 777s fitted with the same Pratt & Whitney engines as the United flight 328 plane.

Pratt & Whitney has dispatched a team to work with investigators. It said it would be “actively coordinating with operators and regulators to support the revised inspection interval of the Pratt & Whitney PW4000 engines that power Boeing 777 aircraft”.

Steve Dickson, the FAA administrator, said the agency was meeting Boeing and Pratt & Whitney as a result of the incident at the weekend. “Based on the initial information, we concluded that the inspection interval should be stepped up for the hollow fan blades that are unique to this model of engine, used solely on Boeing 777 aeroplanes,” he said. 

The Japanese transport ministry said it had ordered stepped-up maintenance on the engines after a serious incident in December when a 777 suffered engine problems on departure from Naha airport in Okinawa.

The ministry said 32 aircraft were registered in Japan with the PW4000 engine: 13 operated by Japan Airlines and 19 belonging to All Nippon Airways.

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