The Pentagon said on Wednesday that no additional cracks have been found on F-35 fighter engines during inspections begun after the February 19 incident.
Pratt began investigating the cracked blade on Sunday evening after the blade assembly arrived at its Middletown, Connecticut, facility, first through nondestructive testing such as X-rays, followed by a procedure that split open the blade for a closer examination.
Those tests have convinced the company's engineers that the problem with the turbine was not caused by high-cycle fatigue, which could force a costly design change, or a design defect, sources familiar with the investigation told Reuters earlier this week.
Instead, engineers now believe the crack is a "creep rupture" caused by the fact that the engine on that particular test plane had been run particularly hard at hot temperatures since it was used for after-burner testing, according to a source briefed on the Pratt recommendation.
The source, who was not authorized to speak on the record, said Pratt engineers were continuing to study the crack to better understand the root cause and develop "potential changes needed to mitigate future occurrences," said the source.
But it was clear that normal fleet use would not reach that degree of "hot time" for a period of years, the source added.
(Reporting by Andrea Shalal-Esa in Washington; editing by Matthew Lewis)
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