(Recasts with comments from Pentagon top weapons buyer, RIAT statement)
RAF FAIRFORD, England, July 10 (Reuters) - The Pentagon's chief weapons buyer told lawmakers there was "growing evidence" that an engine fire on an Air Force F-35A jet last month was not a systemic issue, which sources familiar with the situation said could pave the way for officials to lift an order grounding the fleet of warplanes.
The Pratt & Whitney engine on one of Lockheed Martin Corp.'s Joint Strike Fighters broke apart and caught fire while preparing to take off from a Florida air base on June. 23.
Defense Undersecretary Frank Kendall said on Thursday that all existing engines had been inspected and that no issues similar to the one that caused the engine failure were found, but an examination of the affected engine was continuing.
"We really want to get at the root cause of this to determine exactly what caused it," Kendall told a hearing of the House Armed Services Committee.
"There's a growing body of evidence that this may have been an individual situation, not a systemic one. But we don't know that for certain at this point in time," he added.
Two sources familiar with the situation said U.S. and foreign officials could agree to resume flights of the F-35 jets soon but would probably require regular inspections of the engine part involved in the June fire.
Lifting the grounding order now would allow a small number of F-35s to travel across the Atlantic to appear in one of two air shows this month, possibly as early as Saturday, the sources said.
Organizers of Britain's Royal International Air Tattoo (RIAT) on Thursday said the planes would not appear at their event, which they describe as the world's largest military airshow.
British Defence Secretary Philip Hammond said on Wednesday that while the F-35 might miss the Air Tattoo, he was optimistic it would fly at the Farnborough International Airshow, which starts on July 14.
The F-35 is the world's biggest arms program at $398.6 billion, and failure to appear at both the Air Tattoo and Farnborough show could undermine export interest in the jet just as several countries including Canada and Denmark, both of which helped fund development of the plane, are weighing orders.
Air Force Lieutenant General Christopher Bogdan, who runs the F-35 program for the Pentagon, told reporters in England that safety was paramount and that U.S. and UK authorities were waiting for more data before allowing flights of the F-35 fleet to resume.
Bogdan said he was glad the incident occurred on the ground and that the pilot and emergency crew were not injured. He said it was easier to deal with an issue early in the program, when there are about 150 engines in production or already delivered, as opposed to later when thousands of engines will be in use.
He said the program remained fundamentally on track despite the incident, given the additional margins included during a recent restructuring. (Additional reporting by Mark Potter; editing by Jane Baird)