Metal fatigue apparently played a role in the engine explosion on a United Airlines flight over Denver on Saturday, National Transportation Safety Board President Robert Sumwalt said at a virtual news conference on Monday night. The explosion of Flight 328 caused pieces of the Pratt & Whitney PW4000 engine housing to rain in suburban neighborhoods.
According to CBS Denver, Sumwalt said the engine made a big bang and started vibrating about four minutes after taking off from Denver International Airport. He said the plane was about 12,000 feet above homes at the time.
Sumwalt said that two engine fan blades broke – one at the base where it meets the hub and the second in the middle. He said the first blade caused “overload damage” to the second blade.
NTSB
One of the blades was found on a football field.
Sumwalt said investigators will try to determine how long the blades have been fatigued.
Federal Aviation Administration records show that the plane involved was almost 26 years old, says CBS Denver, but FAA and NTSB officials said they could not clarify whether the engine that failed was an original part or was installed later.
Photos taken on Saturday after the plane returned to Denver airport show a hole under the right wing, suggesting that some of the engine’s wreckage hit the plane itself.
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Sumwalt acknowledged that the lower body of the aircraft was damaged, but said the damage was not structural. The damaged part is a composite fairing that softens the plane to make it more aerodynamic.
Sumwalt said the fire handle in the cabin was activated and two bottles of fire in the engine were discharged. He said the flow of fuel was stopped and investigators will investigate what continued to fuel the fire, despite precautions that were taken.
The engine check will include an analysis of the maintenance history.
Sumwalt added that the agency will compare this event with others in the past.
“Our mission is to understand not only what happened, but why it happened, so that we can prevent it from happening again,” emphasized Sumwalt.
More than 200 passengers were on the flight to Hawaii. No one was hurt on the plane or on the ground. The aircraft returned safely to the airport about 20 minutes after takeoff.
The Denver incident occurred in December, involving a Japan Airlines 777 with the same engine type, as well as an engine problem on a United flight in February 2018.
“There may be a common theme” between the three incidents “, but until the investigation is completed, we don’t know that,” said Scott Hamilton of the aviation news website Leeham News.
Boeing said on Monday that all 128 of the 777s with the same Pratt & Whitney engines were landed worldwide after Saturday’s emergency landing. Sixty-nine were in service and 59 were in storage.
In addition to United, which left 24 planes out of service, the affected operators included Japan’s Japan Airlines and All Nippon and South Korea’s Asiana and Korean Air.
Egyptian state newspaper Al Ahram reported on Monday that national carrier Egyptair is landing four planes with the Pratt & Whitney engine, although they were not in service, a source close to the manufacturer said.
British Transport Secretary Grant Shapps announced a temporary ban on the entry of Pratt & Whitney 4000-112 series jets into UK airspace.
– Agence France-Presse contributed to this report.