Following Japan’s grounding of all Boeing 777s equipped with Pratt & Whitney PW4000-112 turbofans, the U.S. FAA late Sunday said it would issue an emergency airworthiness directive requiring immediate or “stepped up” inspections of the airplanes in reaction to a major engine failure aboard a United Airlines 777-200 on Saturday. The order came as United Airlines, the only U.S. operator of the airplanes in question, said it had grounded its fleet of 24 after consultations with Boeing and the FAA.
Boeing, meanwhile, has recommended the grounding of all 69 of the airplanes in service and another 59 in storage “until the FAA identifies the appropriate inspection protocol.” Along with the 24 airplanes still in service with United, another 19 flew for All Nippon Airways and 13 for Japan Airlines. The remainder flew for Korean Air and Asiana, both of which said they would also ground their fleets.
In a statement, FAA Administrator Steve Dickson shed light on investigators’ focus on the hollow fan blades unique to the PW4000s in the 777. Those blades have come under scrutiny in the past, following a similar incident in 2018 involving the same model of airplane operated by United Airlines. In this case, the National Transportation Safety Board's initial inspection found one blade fractured at the root, an adjacent blade fractured at about mid-span, and a portion of one embedded in the containment ring. The remainder of the blades showed damage to the tips and leading edges.
NTSB investigators continue to analyze debris that rained over a mile-long area of a Denver suburb on Saturday as a result of the engine failure, which happened soon after United Flight 328 took off from Denver International Airport on its way to Honolulu. The airplane turned around and safely landed in Denver at about 1:30 pm. None of the 241 passengers and crewmembers nor anyone on the ground suffered injuries.
Television footage showed a nearly intact nacelle inlet lip from the PW4000-112 lying in the front yard of a suburban home in Broomfield, Colorado, roughly 30 miles west of the airport. More large engine cowl pieces landed at a nearby athletic field. Cell phone video footage taken by passengers in the airplane showed nearly the entire cowling from the right engine missing while the engine itself spewed flames from its core.
An almost identical incident in 2018 involving a United Airlines Boeing 777-200 happened as the airplane approached Honolulu. In that case, the cowling surrounding the right PW4000-112 fell off some 45 minutes before the airplane landed. Investigators found that a fractured fan blade caused the failure. Last year the NTSB determined that insufficient training for a thermal acoustic imaging (TAI) inspection process developed by Pratt & Whitney led to technicians misdiagnosing a problem with the fan blade that ultimately failed in the 2018 incident. Since then Pratt developed a formal training curriculum for the inspections and the FAA issued an airworthiness directive in March 2019 requiring repetitive inspections of all PW4000s in service.
This past December yet another case of a PW4000 failure involved a Japan Airlines 777-200 traveling from Naha Airport in Okinawa to Tokyo Narita Airport. That airplane also landed safely after returning to Naha Airport. The investigation into that incident continues as well.