The chairman of the National Transportation Safety Board said a preliminary assessment has revealed that damage to a fan blade in the engine that failed on a United Airlines Boeing 777-200 is consistent with metal fatigue.
The Pratt & Whitney PW4000 engine failed with a “loud bang” four minutes after takeoff off Saturday from Denver, causing minor damage to the fuselage, NTSB Chairman Robert Sumwalt told reporters Monday after an initial analysis of the flight data and cockpit voice recorders.
He said it was unclear whether the mishap is consistent with an engine failure on another Hawaii-bound United flight in February 2018 that was attributed to a fatigue fracture in a fan blade.
“What is important that we really truly understand the facts, circumstances and conditions around this particular event before we can compare it to any other event,” Sumwalt said at a news briefing.
The engine involved in Saturday’s incident on the 26-year-old aircraft is used on 128 planes — or less than 10 percent of the worldwide fleet of more than 1,600 Boeing 777s, according to Reuters.
In an incident from December 2020, two damaged fan blades were reported in a Japan Airlines Boeing 777 with a PW4000 engine, according to Japan’s Transport Safety Board. That probe is ongoing.
The Federal Aviation Administration said Monday that it had already been evaluating whether to adjust fan blade inspections in the wake of the December incident in Japan.
The United engine’s fan blade will be examined Tuesday after being flown to a Pratt lab where it will examined under supervision of NTSB investigators.
Boeing has recommended that airlines suspend the use of the 777 planes while the FAA identified an appropriate inspection protocol.
The agency has said it plans to issue an emergency airworthiness directive that will require stepped-up inspections of the fan blades for fatigue.
“United Airlines has grounded all of the affected airplanes with these engines, and I understand the FAA is also working very quickly as well as Pratt & Whitney has reiterated or revised a service bulletin,” Sumwalt said. “It looks like action is being taken.”
He said the United incident was not considered an uncontained engine failure because the containment ring contained the parts as they were flying out.
The NTSB will look into why the cowling separated from the jetliner and also why there was a fire despite indications that fuel to the engine had been shut off, Sumwalt added.
Industry sources said that although the engine is made by Pratt, the cowling is manufactured by Boeing, which referred questions on the part to the NTSB.
Pratt & Whitney, which is owned by Raytheon Technologies Corp., has recommended airlines increase inspections in a plan that is being reviewed by the FAA, sources with knowledge of the matter told Reuters.
With Post wires