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Investigation reveals cause of Denver plane explosion that led to global grounding of Boeing 777s

The Independent logo The Independent 5 days ago James Crump
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A preliminary investigation has revealed that a damaged fan blade caused the Denver mid-air engine fire that has led to the grounding of more than 100 Boeing 777s.

Federal investigators believe that wear and tear caused the fan blade to fracture and break off the Pratt & Whitney engine during the Hawaii-bound United Airlines flight on Saturday, National Transportation Safety Board (NTSB) chairman Robert Sumwalt said on Monday.

The chairman told reporters that after it broke, the blade chipped off half of a second blade, leading to multiple pieces of debris to fall to the ground in areas of Denver.

The damaged starboard engine of United Airlines flight 328, a Boeing 777-200, is seen following a February 20 engine failure incident, in a hangar at Denver International Airport in Denver, Colorado, U.S. February 22, 2021. National Transportation Safety Board/Handout via REUTERS.  THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY. THIS IMAGE WAS PROCESSED BY REUTERS TO ENHANCE QUALITY, AN UNPROCESSED VERSION HAS BEEN PROVIDED SEPARATELY.  MANDATORY CREDIT © Thomson Reuters The damaged starboard engine of United Airlines flight 328, a Boeing 777-200, is seen following a February 20 engine failure incident, in a hangar at Denver International Airport in Denver, Colorado, U.S. February 22, 2021. National Transportation Safety Board/Handout via REUTERS. THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY. THIS IMAGE WAS PROCESSED BY REUTERS TO ENHANCE QUALITY, AN UNPROCESSED VERSION HAS BEEN PROVIDED SEPARATELY. MANDATORY CREDIT

The engine failed just four minutes into the flight on Saturday, with a “loud bang” heard by passengers, and the preliminary assessment shows that the damage to the fan blade is consistent with metal fatigue.

Mr Sumwalt revealed that despite the dramatic nature of the incident, there was only minor damage to the aircraft body and no structural damage.

No one onboard was injured in the incident on Saturday, as the United Airlines plane returned safely to Denver International Airport shortly after the engine problem.

BROOMFIELD, CO - FEBRUARY 20: Pieces of an airplane engine from Flight 328 sit scattered in a neighborhood on February 20, 2021 in Broomfield, Colorado. An engine on the Boeing 777 exploded after takeoff from Denver prompting the flight to return to Denver International Airport where it landed safely. (Photo by Michael Ciaglo/Getty Images) © 2021 Getty Images BROOMFIELD, CO - FEBRUARY 20: Pieces of an airplane engine from Flight 328 sit scattered in a neighborhood on February 20, 2021 in Broomfield, Colorado. An engine on the Boeing 777 exploded after takeoff from Denver prompting the flight to return to Denver International Airport where it landed safely. (Photo by Michael Ciaglo/Getty Images)

Although aircraft debris fell next to homes, gardens and soccer fields in Denver on Saturday, there was also no injuries reported on the ground.

The recovered pieces of debris are being flown to a Pratt & Whitney laboratory for examination on Tuesday, which will be supervised by NTSB investigators.

The investigators will also look over maintenance records to check to see whether problems may have been missed during safety inspections prior to the flight.

In this photo provided by the Broomfield Police Department on Twitter, debris is scattered in the front yard of a house at near 13th and Elmwood, Saturday, Feb. 20, 2021, in Broomfield, Colo. A commercial airliner dropped debris in Colorado neighborhoods during an emergency landing Saturday. The Broomfield Police Department said on Twitter that the plane landed safely at Denver International Airport and that no injuries had been reported from the incident.  (Broomfield Police Department via AP) © ASSOCIATED PRESS In this photo provided by the Broomfield Police Department on Twitter, debris is scattered in the front yard of a house at near 13th and Elmwood, Saturday, Feb. 20, 2021, in Broomfield, Colo. A commercial airliner dropped debris in Colorado neighborhoods during an emergency landing Saturday. The Broomfield Police Department said on Twitter that the plane landed safely at Denver International Airport and that no injuries had been reported from the incident. (Broomfield Police Department via AP)

More than 100 Boeing 777s that use the same engine as the Denver United Airlines flight have been grounded in the wake of the incident, while the Federal Aviation Administration (FAA) investigates Pratt & Whitney blades.

Boeing recommended that the planes be grounded after Japanese safety regulators banned 777s with the same Pratt & Whitney 4000 engines, and United said it had voluntarily grounded its fleet on Sunday.

A couple of similar incidents have occurred over the past few years, and the FAA revealed on Monday that it was already considering adjusting fan blade inspections, following a problem with an engine during a Japanese flight in December 2020.

BROOMFIELD, CO - FEBRUARY 20: Pieces of an airplane engine from Flight 328 sit scattered in a neighborhood on February 20, 2021 in Broomfield, Colorado. An engine on the Boeing 777 exploded after takeoff from Denver prompting the flight to return to Denver International Airport where it landed safely. (Photo by Michael Ciaglo/Getty Images) © 2021 Getty Images BROOMFIELD, CO - FEBRUARY 20: Pieces of an airplane engine from Flight 328 sit scattered in a neighborhood on February 20, 2021 in Broomfield, Colorado. An engine on the Boeing 777 exploded after takeoff from Denver prompting the flight to return to Denver International Airport where it landed safely. (Photo by Michael Ciaglo/Getty Images)

Although similar incidents are likely to be looked at, Mr Sumwalt stressed that what is important is “that we really truly understand the facts, circumstances and conditions around this particular event before we can compare it to any other event.”

Although the preliminary findings points to metal fatigue, NTSB inquiries can take up to a year to complete as all avenues will be looked at.

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

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