The U.S. National Transportation Safety Board confirmed late Feb. 21 that two fractured fan blades are among the damage found in its probe of a catastrophic engine failure which forced a United Airlines Boeing 777-200 to return to Denver International Airport on Feb. 20 shortly after takeoff.
Meanwhile, the FAA was finalizing an emergency inspection order targeting the blades, and Boeing is calling for operators not to operate affected aircraft until the new protocols are in place.
FAA Administrator Steve Dickson late Feb. 21 said the agency will order “immediate or stepped-up” inspections of Pratt & Whitney PW4000 fan blades.
“Based on the initial information, we concluded that the inspection interval should be stepped up for the hollow fan blades that are unique to this model of engine,” Dickson said.
FAA was meeting with Boeing and Pratt & Whitney representatives to finalize the inspection order, he added.
Boeing said operators of PW4000-powered 777s should keep them out of service until the U.S. agency acts.
"While the [National Transportation Safety Board, or NTSB] investigation is ongoing, we recommended suspending operations of the 69 in-service and 59 in-storage 777s powered by Pratt & Whitney 4000-112 engines until the FAA identifies the appropriate inspection protocol,” the manufacturer said late Feb. 21.
Boeing’s statement came after the only U.S. operator, United Airlines, pulled its 24 affected aircraft from service, and Japan’s regulator ordered its airlines to ground them.
"We will continue to work closely with regulators to determine any additional steps and expect,” United said.
Japan's Ministry of Land, Infrastructure, Transport and Tourism ordered all PW4000-powered 777s flown by its country's airlines grounded until further notice.
NTSB in an investigative update late Feb. 21 said two blades were damaged. One was fractured “near the root,” and an “adjacent fan blade was fractured about mid-span.”
Investigators found part of one blade imbedded in the engine’s containment ring, and the “remainder of the fan blades exhibited damage to the tips and leading edges," NTSB said. Damage to the airplane was “minor."
The incident, which took place as the 1994-built aircraft was in the initial climb phase bound for Honolulu, led to debris from the No. 2 Pratt & Whitney PW4077 being scattered over Broomfield, Colorado, a city to the northwest of Denver. Video of the event taken from inside the cabin and images of debris on the ground pointed to not only a fan blade failure, but also the loss of the inlet cowl lip and nacelle casing.
The 777-200, which was operating United’s Flight 328 with 231 passengers and 10 crew, landed safely. There were no injuries reported on the aircraft or ground.
The Colorado event appears to be strikingly similar to recent PW4077 fan blade-related failures in which inlets or cowling parts detached. These include an incident on Feb 13, 2018, involving a sister aircraft to the most recent 777-200 mishap, in which the No. 2 engine failed 30-min. before landing while en route from San Francisco to Honolulu. The NTSB cited shortcomings in Pratt's inspection processes for setting the stage for that accident.
More recently, on Dec 4, 2020, the No. 1 engine on a Japan Airlines 777-200 lost a fan blade shortly after takeoff on a flight from Okinawa, Japan to Tokyo.
In the wake of the 2018 incident the FAA issued a directive in March 2019 requiring initial and recurring inspections of the fan blades on the PW4000. It is not yet known if the blades involved in the United 328 event had been through this inspection.
This story has been updated with information from the FAA, NTSB, Boeing, and United Airlines.