The Pentagon lifted its grounding of the new F-35 jet fighter on Thursday after concluding that a turbine blade had cracked on a single plane after it was overused in test operations.
The office that runs the program said no other cracks were found in inspections of the other engines made so far, and no engine redesign was needed.
It said the engine in which the blade cracked was in a plane that “had been operated at extreme parameters in its mission to expand the F-35 flight envelope.”
The program office added that “prolonged exposure to high levels of heat and other operational stressors on this specific engine were determined to be the cause of the crack.”
All flights were suspended last week for the 64 planes built so far once the crack, which stretched for six-tenths of an inch, was found during a routine inspection.
Pratt & Whitney, which makes the engines, investigated the problem with military experts. The company, a unit of United Technologies, said on Wednesday that the crack occurred after that engine was operated more than four times longer in a high-temperature flight environment than the engines would in normal use.
The F-35, a supersonic jet meant to evade enemy radar, is the Pentagon’s most expensive program and has been delayed by various technical problems. The program could cost $396 billion if the Pentagon builds 2,456 jets by the late 2030s.
F-35 Jets Returned to Service by Pentagon
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F-35 Jets Returned to Service by Pentagon
