Metal fatigue apparently played a role in theNational Transportation Safety Board Chairman Robert Sumwalt said in a virtual press conference Monday night. The explosion of Flight 328 rained pieces of the Pratt & Whitney PW4000 engine crankcase over suburban neighborhoods.
According to CBS Denver, Sumwalt said the engine made a loud bang and started 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 aircraft involved was nearly 26 years old, CBS Denver said, but FAA and NTSB officials said they couldn’t clarify whether the failed engine was a genuine part or was 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 struck 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 fire handle in the cockpit 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 precautions being taken.
The engine review will include an overview of 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 followed 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 all 128,777 powered by the same Pratt & Whitney engines were grounded around the world following the emergency landing on Saturday. Sixty-nine were in service and 59 were in storage.
In addition to United, which decommissioned 24 planes, the carriers concerned included Japanese companies Japan Airlines and All Nippon and South Koreans Asiana and Korean Air.
Egyptian state newspaper Al Ahram reported Monday that the national carrier Egyptair was grounding four planes equipped with the Pratt & Whitney engine, although 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.