Boeing on Sunday recommended that airlines stop flying versions of the aircraft that are equipped with Pratt & Whitney 4000-112 engines while US authorities investigate the Denver incident.
“Boeing is actively monitoring recent events related to United Airlines Flight 328. While the NTSB investigation is ongoing, we recommended suspending operations of the 69 in-service and 59 in-storage 777’s powered by Pratt & Whitney 4000-112 engines until the FAA identifies the appropriate inspection protocol.
Boeing supports the decision yesterday by the Japan Civil Aviation Bureau, and the FAA’s action today to suspend operations of 777 aircraft powered by Pratt & Whitney 4000-112 engines. We are working with these regulators as they take actions while these planes are on the ground and further inspections are conducted by Pratt & Whitney.
Updates will be provided as more information becomes available."
United Airlines, Korean Air, Asiana Airlines, All Nippon Airways and Japan Airlines all use Boeing 777’s powered by Pratt & Whitney 4000 engines.
The groundings come after an engine utilised on a United-operated B777 failed Saturday, just minutes after the Honolulu-bound flight took off from Denver International Airport. As United Flight 328 returned to the airport, it dropped engine debris through the roofs of homes and into yards.
An initial examination of the Pratt & Whitney PW4077 engine from that flight showed that two fan blades were fractured, according to the US National Transportation Safety Board (NTSB). The agency said that the remaining blades exhibited damage "to the tips and leading edges."
The findings are preliminary, but they were still enough to spur some airlines to pull planes that use the PW 4000 series from service. The NTSB said that it will examine the engine, airline and photos and videos taken by passengers on board the flight, along with the flight data and cockpit voice recorders.
United said Sunday that it would immediately pull 24 planes from service "out of an abundance of caution." The company said its move was voluntary and temporary and should disrupt only "a small number of customers."
Japan's transportation ministry, meanwhile, said that it had ordered All Nippon Airways and Japan Airlines to ground planes using that series of engines. The ministry said that the order applied to 19 Boeing 777’s at All Nippon Airways and 13 at Japan Airlines that have Prat & Whitney 4000 engines.
South Korea's Asiana Airlines, which owns nine of the planes, said it would stop using them, too. The jets are also used by Korean Air, which on Tuesday said it would ground the planes. The airline has six of the jets in service, while 10 are in storage.
According to the most recent registry data, the only airlines that operate with the affected engines are in the United States, Japan and South Korea. United is the only US operator with this type of engine in its fleet.
Both Boeing and Pratt & Whitney have said they are cooperating with the US investigation into the Denver incident. "We are pleased to hear that United Airlines flight 328 returned safely to Denver," Boeing said in a statement. "Boeing technical advisers are supporting the US National Transportation Safety Board with its investigation."
Pratt & Whitney said it has sent a team to work with investigators looking into the engine failure.
"Pratt & Whitney is actively coordinating with operators and regulators to support the revised inspection interval" of the 4000 engines that power certain 777s," the company said, adding that "any further investigative updates regarding this event will be at the discretion of the NTSB."
The US Federal Aviation Administration on Sunday also issued an emergency order saying it would be stepping up inspections of 777s that use certain Pratt & Whitney 4000 engines.
"We reviewed all available safety data following the incident," FAA Administrator Steve Dickson said. "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, used solely on Boeing 777 aircraft."
The engine failure is another blow for Boeing after its 737 Max aircraft was grounded for 18 months following two aviation accidents that left 346 people dead.