Parts of the aircraft in a Denver backyard following engine explosion
Hours earlier, in the Netherlands, one of four engines on a Boeing 747-412 cargo plane failed within minutes of its departure from Maastricht.
Blade fragments were ejected from the Pratt & Whitney 4056 engine, coming down on the Dutch village of Meerssen. Two people were slightly injured, with the debris also damaging houses and cars.
The plane, which was en route to New York, made an emergency landing at Liege airport in Belgium.
Engine debris lands on a car in Holland
United Airlines said it was grounding its fleet of 52 Boeing 777s that used the Pratt & Whitney 4000 series engines. Only 24 of them were in active service.
“Since yesterday, we’ve been in touch with regulators at the NTSB and FAA and will continue to work closely with them to determine any additional steps that are needed to ensure these aircraft meet our rigorous safety standards and can return to service,” the company said in an emailed statement.
In a separate move, Japanese authorities grounded its Boeing 777s also using Pratt & Whitney engines. Japan said ANA operated 19 of the type and JAL operated 13 of them, though the airlines said their use had been reduced during the pandemic. JAL said its fleet was due for retirement by March 2022.
Saturday’s incidents came less than three months after the failure of another Pratt & Whitney 4000 series engine when pilots on a Boeing 777 were forced to turn back after an engine explosion six minutes after taking off from Okinawa en route to Tokyo.
And in February 2018 another Pratt & Whitney 4000 series engine failed when a blade broke off on a United Airlines flight from San Francisco to Hawaii.
In all four incidents, the pilots succeeded in making an emergency landing without anybody on board being injured.
Residents take pictures of debris fallen from a United Airlines airplane's engine on the neighborhood of Broomfield, outside Denver
Credit: AFP
While the incident doesn’t suggest broader problems with the 777, it adds another urgent issue to Boeing’s to-do list only just after the 737 Max was cleared to fly again in markets including the US and Europe. The company has halted deliveries of its 787 Dreamliners to check for manufacturing flaws.
“We recommended suspending operations of the 69 in-service and 59 in-storage 777s powered by Pratt & Whitney 4000-112 engines until the FAA identifies the appropriate inspection protocol,” Boeing said in a statement, adding that it supports decisions by the FAA and Japan’s Civil Aviation Bureau to temporarily ground aircraft powered by the engines.
United is the only US operator of the planes, according to the Federal Aviation Administration (FAA). The other airlines using them are in Japan and South Korea, the U.S. agency said.
South Korea’s transport ministry said it was looking into the issue.
United Airlines flight UA328 returns to Denver International Airport with its starboard engine on fire
Credit: Hayden Smith/@speedbird5280
/Reuters
Korean Air has PW4090 engines on 12 777-200s and four 777-300s. More than half of those planes are in storage due to the pandemic. Asiana Airlines has nine 777s with the Pratt engines, but most of them are also grounded due to Covid-19.
Only 60 Pratt-powered 777-200 and -300 models are still flying globally, according to analysis of Cirium data by George Ferguson at Bloomberg Intelligence. Another 67 of the jets are sitting in storage, although they haven’t officially been retired.
The latest inspections could hasten the end of the earliest 777 models if the repairs turn out to be costly, Mr Ferguson said. “They are already out of favor because of their size and the pandemic.”
Pratt & Whitney, owned by Raytheon Technologies Corp , said it was coordinating with operators and regulators to support a revised inspection interval for the engines.
The FAA’s inpection order only applies to US-registered Boeing 777 aircraft.
FAA Administrator Steven Dickson said the aggressive inspections “will likely mean that some airplanes will be removed from service.” The exact details of what type of inspections will be needed and how quickly they must be done are still being worked out, Dickson said.
“After consulting with my team of aviation safety experts about yesterday’s engine failure aboard a Boeing 777 airplane in Denver, I have directed them to issue an Emergency Airworthiness Directive that would require immediate or stepped-up inspections of Boeing 777 airplanes equipped with certain Pratt & Whitney PW4000 engines,” Dickson said in an emailed statement.
In addition, the National Transportation Safety Board, the US aviation watchdog, has already announced an inquiry into the weekend’s incident in Denver.
Pete Buttigieg, the newly-appointed US Transportation Secretary, said he would work with the NTSB to "understand any lessons learned in a way that will maximize the sense of safety every time we get on a plane."
Passengers on the flight from Denver to Honolulu feared the worst as the right engine exploded.
"The pilot did a hell of a job," New York-based aviation consultant Bob Mann told The Telegraph.
Mr Mann believes investigators will focus on the design of the engine blades.
"There is a working theory that these very large, light blades may be migrating forward as they fail, which causes them to escape from the containment ring.
"Regulators and designers should be looking at the fan case and containment ring. The idea is over time these blades have become much lighter: it may be that the failure modes aren’t the same.
"Everything is lighter. The whole game is to get as much thrust possible — and these failures generally occurred at takeoff thrust — with the least amount of mass.
"I think the technology has outstripped the standardised testing regime which was designed in the 1960s."
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