Metal fatigue apparently played a role in the engine explosion on a United Airlines flight over Denver on Saturday, National Transportation Safety Committee Chairman Robert Sumwalt said Monday night. The explosion on Flight 328 sent pieces of the Pratt & Whitney PW4000 engine casing raining in the suburbs.
According to CBS Denver, Sumwalt said the engine made a loud noise and began vibrating about four minutes after takeoff from Denver International Airport. He said the plane was about 12,000 meters above the houses at the time.
Sumwalt said two blades of the engine fan broke – one at the base where it meets the hub and the other halfway. 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 tired.
Federal Aviation Administration records show the plane was nearly 26 years old, says CBS Denver, but FAA and NTSB officials said they could not clarify whether the faulty engine was an original part or was later installed.
Photographs taken Saturday after the plane returned to Denver airport show an open hole under its right wing, suggesting that some of the engine debris hit the plane itself.
NTSB
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 smoothes the plane to make it more aerodynamic.
Sumwalt said the fire handle in the cabin had been activated and that two fire bottles from the engine had been unloaded. He said the fuel flow was stopped and investigators will look into what continued to fuel the fire, despite precautions being taken.
The engine review will include a look at its maintenance history.
Sumwalt added that the agency will compare this event with others from 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 said.
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 was followed by one in December, which 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” among the three incidents, “but by the time the investigation is completed, we don’t know,” Scott Hamilton told Leeham News.
Boeing said Monday that all 128 of the 777s with the same Pratt & Whitney engines were grounded worldwide following Saturday’s emergency landing. Sixty-nine were on duty and 59 were stored.
In addition to United, which took 24 aircraft out of service, the affected carriers included Japan Airlines and All Nippon in Japan and Asiana and Korean Air in South Korea.
The Egyptian state newspaper Al Ahram reported on Monday that the national carrier Egyptair lands four planes with the Pratt & Whitney engine, although they were not in operation, a source close to the manufacturer said.
British Transport Secretary Grant Shapps has announced a temporary ban on Pratt & Whitney 4000-112 series airplanes from entering British airspace.
– France-Presse contributed to this report.