In a statement, Robert Sumwalt, the chairman of the U.S. National Transportation Safety Board (NTSB) stated, according to a preliminary assessments, the damage to the fan blade in the Pratt & Whitney engine which failed in the United Airlines Boeing 777-200 is consistent with metal fatigue.
At a news briefing, Sumwalt said it was not immediately clear whether the Saturday’s failure of the PW4000 engine shortly after takeoff was consistent with another engine failure on another Hawaii-bound United flight in February 2018 which incidentally was also attributed to metal fatigue in the fan blade.
In December 2020, Japan’s Transport Safety Board had reported it found two damaged fan blades of the PW4000 engine on a Japan Airlines 777, in a separate incident, with one showing a metal fatigue crack.
The United engine’s fan blade is set to be examined later today at a Pratt & Whitney laboratory where it will be examined under supervision of NTSB investigators.
“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,” said Sumwalt.
The U.S. Federal Aviation Administration plans on issuing an emergency airthworthiness directive that requires airlines to step-up their inspections of fan blades for metal fatigue.
In March 2019, following the February 2018 United engine failure which was attributed to fan blade fatigue, the FAA had ordered inspections every 6,500 cycles.
According to Sumwalt, “the United incident was not considered an uncontained engine failure because the containment ring contained the parts as they were flying out”; he went on to add, while there was some minor damage to the aircraft body but no structural damage to the aircraft.
NTSB will look into why the engine cowling separated from the plane and also why there was a fire despite indications fuel to the engine had been turned off, said Sumwal.