Metal fatigue apparently played a role in the engine explosion of United Flight 328 over Denver, NTSB chief said

Metal fatigue apparently played a role in the engine explosion on a United Airlines flight over Denver on Saturday, National Transportation Safety Board Chairman Robert Sumwalt told a virtual press conference Monday evening. The explosion of Flight 328 sent pieces of the Pratt & Whitney PW4000 engine crankcase raining down on suburban neighborhoods.

According to CBS Denver, Sumwalt said the engine made a loud noise and began to vibrate about four minutes after takeoff from Denver International Airport. He said the plane was about 12,000 feet above the houses at the time.

Sumwalt said two fan blades in the motor broke – one at the base where it meets the hub and the second halfway. He said the first blade caused “overload damage” to the second blade.

One of the blades was found on a football field.

Sumwalt said investigators will try to determine how long the blades have been suffering from fatigue.

Federal Aviation Administration records show the involved plane was nearly 26 years old, according to CBS Denver, but FAA and NTSB officials said they couldn’t clarify whether the failed engine was a part of it. ‘origin or had been installed later.

Photos taken on Saturday after the plane returned to Denver airport show a gaping hole under the right wing, suggesting some of the engine debris hit the plane itself.

Sumwalt admitted that the aircraft’s underbody was damaged, but said the damage was not structural. The damaged part is a composite fairing that smooths the aircraft to make it more aerodynamic.

Sumwalt said the cockpit fire handle was activated and two fire cylinders in the engine were discharged. He said the fuel flow had been cut off and investigators would look into what continued to fuel the fire despite the precautions that were taken.

Examining the engine will include a look at its maintenance history.

Sumwalt added that the agency will compare this event to others in the past.

“Our mission is to understand not only what happened, but also why it happened so that we can prevent it from happening again,” Sumwalt stressed.

More than 200 passengers were on the flight to Hawaii. No one was injured on the plane or on the ground. The aircraft returned safely to the airport approximately 20 minutes after takeoff.

The Denver incident follows the December incident involving a Japan Airlines 777 with the same type of engine as well as an engine problem on a United flight in February 2018.

“There might be a common theme ‘among the three incidents’ but until the investigation is complete we don’t know,” said Scott Hamilton, of the aviation news site Leeham News.

Boeing said on Monday that all 128 of the 777s fitted with the same Pratt & Whitney engines had been grounded around the world following the emergency landing on Saturday. Sixty-nine were in service and 59 were in stock.

In addition to United, which took 24 planes out of service, the carriers affected included Japan Airlines and All Nippon and Asiana and Korean Air of South Korea.

Egyptian state newspaper Al Ahram reported on Monday that the national airline Egyptair had grounded four planes equipped with the Pratt & Whitney engine while they were not in service, a source close to the manufacturer said.

UK Transport Secretary Grant Shapps has announced a temporary ban on jets powered by Pratt & Whitney 4000-112 series engines from entering UK airspace.

– Agence France-Presse contributed to this report.