Dutch and US investigators launch investigation after aircraft scatter engine debris

The  US Federal Aviation Administration has issued an emergency airworthiness directive calling for the inspection of Boeing 777s after two aircraft using the same family of engines showered debris on the ground shortly after take-off. United Airlines said it was grounding its fleet of 52 Boeing 777s that used the Pratt & Whitney 4000 series engines, of which 24 were in active service. In a separate move, the Japanese authorities grounded 32 Boeing 777s also using Pratt & Whitney engines. 

The moves follow two separate incidents on Saturday which saw air safety investigators on both sides of the Atlantic open inquiries. In the Netherlands, one of four engines on a Boeing 747-412 cargo plane failed within minutes of its departure from Maastricht on Saturday. 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.

Engine debris lands on a car in Holland

The plane, which was en route to New York, made an emergency landing at Liege airport in Belgium. Within hours, one of the two Pratt & Whitney 4077 engines on a United Airlines Boeing 777 exploded shortly after it took off from Denver en route to Honolulu. The United aircraft's engine explosion scattered debris over a Denver suburb of Broomfield.

Nobody was injured.

Parts of the aircraft in a Denver backyard following engine explosion

Engines on both aircraft are drawn from the same family, with the 4077 being a new a more powerful version than the 4056. 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. The FAA's inpection order only applies to US-registered Boeing 777 aircraft. In addition, the National Transportation Safety Board, the US aviation watchdog, has already announced an inquiry into the weekend's incident in Denver.

United Airlines flight UA328 returns to Denver International Airport with its starboard engine on fire Credit: Hayden Smith/@speedbird5280/Reuters

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. "I can honestly say I thought we were going to die at one point - because we started dropping altitude right after the explosion," passenger David Delucia told The Denver Post. "The pilot did a hell of a job," New York-based aviation consultant Bob Mann told The Telegraph.

A passenger on United 328 took this video of flames shooting out from the engine.

Some people told me they said prayers and held their loved ones' hands as they looked out the window. Flight was on its way to Hawaii from Denver. Glad everyone onboard is safe #9News pic.twitter.com/c8TNYlugU2

-- Marc Sallinger (@MarcSallinger) February 20, 2021

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."

The Telegraph has approached Pratt & Whitney for comment.

After the 2018 incident, Pratt & Whitney said it supported the NTSB investigation and had taken corrective action.

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