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 said at a virtual press conference Monday. night. The explosion on Flight 328 caused chunks of the Pratt & Whitney PW4000 engine casing to fall on suburban neighborhoods.
According to CBS Denver, Sumwalt said the engine made a loud roar 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 on the motor broke, one at the base where it meets the shaft and the second midway. He said the first sheet caused “overload damage” to the second sheet.
One of the blades was found on a soccer field.
Sumwalt said the researchers will try to determine how long the blades have suffered from fatigue.
Federal Aviation Administration records show the plane involved was nearly 26 years old, CBS Denver says, but FAA and NTSB officials said they couldn’t clarify whether the engine that failed was an original part or was installed later. .
Photos taken Saturday after the plane returned to the Denver airport show a large hole under the right wing, suggesting that some of the engine debris struck the plane.
Sumwalt acknowledged that the underside of the aircraft was damaged, but said the damage was not structural. The damaged part is a composite fairing that smoothes the plane to make it more aerodynamic.
Sumwalt said the fire handle in the cockpit was activated and two bottles of fire were discharged into the engine. He said the fuel flow was cut off and investigators will investigate what continued to fuel the fire despite the precautions that were taken.
The engine exam 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 emphasized.
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 about 20 minutes after takeoff.
The Denver incident followed one in December that involved a Japan Airlines 777 with the same type of engine, 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 complete, we don’t know,” said Scott Hamilton of the aviation news site Leeham News.
Boeing said Monday that the 128 777s with the same Pratt & Whitney engines were grounded around the world after the emergency landing on Saturday. Sixty-nine were in service and 59 were in storage.
In addition to United, which took 24 aircraft out of service, affected carriers included Japan Airlines and All Nippon of Japan and Asiana and Korean Air of South Korea.
The Egyptian state newspaper Al Ahram reported on Monday that the national airline Egyptair is on the ground four planes with the Pratt & Whitney engine, although they were not in service, said a source close to the manufacturer.
British Transport Secretary Grant Shapps announced a temporary ban on aircraft powered by the Pratt & Whitney 4000-112 series from entering UK airspace.
– Agence France-Presse contributed to this report.