WASHINGTON — The head of the National Transportation Safety Board said Monday that damage to a fan blade in a Pratt & Whitney engine that failed on a United Airlines Boeing 777-200 is consistent with metal fatigue, according to a preliminary assessment.
At a news briefing, NTSB Chairman Robert Sumwalt said it was not clear whether the failure of the PW4000 engine with a "loud bang" four minutes after takeoff Saturday is consistent with an engine failure on another Hawaii-bound United flight in February 2018, which was attributed to a fatigue fracture in a fan blade.
The engine that failed on the 26-year-old Boeing 777, shedding parts over a Denver suburb, was a PW4000 used on fewer than 10 percent of the global fleet of 777 wide-body jets.
Japan's Transport Safety Board reported that it found two damaged fan blades, one with a metal fatigue crack, in another incident in December on Japan Airlines 777 with a PW4000 engine. The investigation continues.
The focus is more on engine maker Pratt & Whitney, and analysts expect little financial impact on Boeing, but the PW4000 issues are another headache for the plane-maker as it recovers from the far more serious 737 MAX crisis. Boeing's flagship narrow-body jet was grounded for nearly two years after two deadly crashes.
The United engine's fan blade was to be examined Tuesday after being flown to a Pratt & Whitney laboratory, where it will be examined under the supervision of NTSB investigators.
"What is important is 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.
Boeing recommended that airlines suspend the use of the planes while the Federal Aviation Administration identified an appropriate inspection protocol, and Japan suspended such flights.
The FAA plans to issue an emergency airworthiness directive soon that will require stepped-up inspections of the fan blades for fatigue.
In March 2019, after the February 2018 United engine failure attributed to fan blade fatigue, the FAA ordered inspections every 6,500 cycles. A cycle is one takeoff and landing.
Sumwalt said the United incident was not considered an uncontained engine failure because the containment ring contained the parts as they were flying out. There was minor damage to the aircraft body but no structural damage, he said.
The NTSB will look into why the engine cowling separated from the plane and why there was a fire despite indications that fuel to the engine had been turned off, he said.
Pratt & Whitney, which is owned by Raytheon Technologies Corp., said Sunday that it was coordinating with regulators to review inspection protocols.
Nearly half of the global fleet of 128 planes operated by United, Japan Airlines, ANA Holdings, Korean Air, Asiana Airlines and other airlines had already been grounded in a plunge in travel demand because of the coronavirus pandemic.