The National Transportation Safety Board on Monday said a maintenance records group will be formed to investigate the Boeing 777 engine’s history after it failed on United Airlines flight #328 and erupted into flames shortly after takeoff on Saturday.
"Our mission is to understand not only what happened but why it happened so we can keep it from happening again," NTSB chairman Robert Sumwalt said at a Monday evening press conference.
Sumwalt emphasized that the investigation is still in its preliminary stages. Asked whether the particular engine had been inspected after another engine failure on a Southwest Airlines flight in 2018, Sumwalt said that was a question that will be answered pending a maintenance group investigation.
Boeing has recommended that airlines ground all 777s with the type of engine that blew apart after takeoff from Denver this past weekend, and most carriers that fly those planes said they would temporarily pull them from service.
The U.S. Federal Aviation Administration ordered United Airlines to step up inspections of the aircraft after one of its flights made an emergency landing at Denver International Airport on Saturday as pieces of the engine's casing rained on suburban neighborhoods. None of the 231 passengers or 10 crew were hurt, and the flight landed safely, authorities said. United is among the carriers that has grounded the planes.
FAA Administrator Steve Dickson identified the focus on the stepped-up inspections as hollow fan blades unique to the Pratt & Whitney PW4000 engine model and used solely on Boeing 777s. Dickson's statement said the conclusion was based on an initial review of safety data and would likely mean grounding some planes.
Boeing said there were 69 of the 777s with the Pratt & Whitney 4000-112 engines in service and another 59 in storage. The company affirmed they should be grounded until the FAA sets up an inspection regime.
The emergency landing is the latest trouble for Boeing, which saw its 737 Max planes grounded for more than a year after two deadly crashes in 2019 and is suffering amid the huge reduction in air travel due to the coronavirus pandemic. The Max planes began returning to the skies late last year.
Video posted on Twitter from Saturday's emergency showed the engine fully engulfed in flames as the plane flew. Freeze frames from different video taken by a passenger sitting slightly in front of the engine and also posted on Twitter appeared to show a broken fan blade in the engine.
Passengers, who were headed to Honolulu, said they feared the plane would crash after an explosion and flash of light, while people on the ground saw huge chunks of the aircraft pour down, just missing one home and crushing a truck. The explosion, visible from the ground, left a trail of black smoke in the sky.
The NTSB said that two of the engine's fan blades were fractured and the remainder of the fan blades "exhibited damage." But it cautioned that it was too early to draw conclusions about what happened.
United says it will work closely with the FAA and the NTSB "to determine any additional steps that are needed to ensure these aircraft meet our rigorous safety standards and can return to service."
The NTSB said the cockpit voice recorder and flight data recorder were transported to its lab in Washington so the data can be analyzed. NTSB investigations can take up to a year or longer, although in major cases the agency generally releases some investigative material midway through the process.
The Associated Press contributed to this report.