Metal fatigue apparently played a role in the engine explosion during a United Airlines flight over Denver on Saturday, National Transportation Safety Council Chairman Robert Sumwalt said at a virtual news conference on Monday night. The explosion on Flight 328 caused pieces of the Pratt & Whitney PW4000 engine casing to rain in suburban neighborhoods.
According to CBS Denver, Sumwalt said the engine blew a hard blow and began vibrating about four minutes after takeoff from Denver International Airport. He said the plane was about 12,000 feet above houses at the time.
Sumwalt said two fan blades broke in the engine – one at the base where it meets the hub and the second about halfway. He said the first blade caused the second blade “damage to overload”.
NTSB
One of the blades was found on a soccer field.
Sumwalt said investigators will try to determine how long the blades had the fatigue.
According to the Federal Aviation Administration, the plane in question was nearly 26 years old, CBS Denver said, but FAA and NTSB officials said they could not explain whether the engine that failed was an original part or was later installed.
Photos taken Saturday after the plane returned to the airport in Denver show a gaping hole under the right wing, indicating that some of the engine debris hit the plane itself.
NTSB
Sumwalt acknowledged that the chassis of the aircraft was damaged, but said the damage was not structural. The damaged part is a composite casing that makes the aircraft smoother to make it more aerodynamic.
Sumwalt said the fire handle in the cabin was activated and two fire bottles in the engine were unloaded. He said the flow of fuel had been turned off, and investigators would investigate what kept the fire going, despite the precautions taken.
The engine search will include the maintenance history.
Sumwalt added that the agency would compare this event to others in the past.
“Our mission is to not only understand what happened, but also why it happened so that we can occur again,” Sumwalt stressed.
More than 200 passengers were on the Hawaii flight. No one was injured in the crash or on the ground. The plane returned safely to the airport about 20 minutes after takeoff.
The incident in Denver follows in December on a Japan Airlines 777 with the same type of engine as well as an engine problem in a February 2018 United flight.
“There’s a common theme ‘between the three incidents,’ but until the investigation is completed, we do not know,” said Scott Hamilton of aviation news website Leeham News.
Boeing said Monday all 128 777s with the same Pratt & Whitney engines were grounded worldwide after the emergency landing on Saturday. Sixty-nine were employed and 59 were in storage.
In addition to United, which took 24 aircraft out of service, the Japanese Airline and All Nippon and Asiana and Korean Air were in South Korea.
Egyptian state newspaper Al Ahram reported on Monday that Egyptians were turning on 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 has announced a temporary ban on jet aircraft entering British airspace with Pratt & Whitney 4000-112 engines.
– Agence France-Presse contributed to this report.