* Suspect lines made by unit of Parker Hannifin-P&W
* F-35B expected to resume flights soon
By Andrea Shalal-Esa
WASHINGTON, Jan 28 (Reuters) - Pentagon and industry investigators have identified a manufacturing problem as the most likely cause of an engine failure that led to the grounding of the Marine Corps version of the Lockheed Martin Corp F-35 fighter jet, a spokesman for engine maker Pratt & Whitney said on Monday.
The F-35B should be able to resume flights as soon as the parts supplied by a unit of Parker Hannifin Corp are replaced, said Matthew Bates, a spokesman for Pratt & Whitney, a unit of United Technologies Corp.
"The team continues to work diligently toward completing the investigation and implementing corrective actions with the supplier. We anticipate a return to flight for the (short takeoff, vertical landing) variant soon," Bates said.
A spokeswoman for Parker Hannifin said the company was working around the clock to support the investigation and makes many components for the aircraft.
The grounding did not affect the Air Force or Navy versions of the new radar-evading fighter since they do not use the same part. The Marine Corp's B-model can take off from short runways and land like a helicopter.
The Pentagon grounded all 25 F-35B jets on Jan. 18 after a "fueldraulic" line, associated with directing the B-model's exhaust, failed just before takeoff during a training flight at Eglin Air Force Base in Florida.
Instead of traditional hydraulic fluid, the line uses fuel as the operating fluid to reduce weight.
Pentagon officials were expected to finalize the finding and the proposed fix at a meeting on Monday, according to sources familiar with the investigation, who were not authorized to speak publicly.
An initial inspection discovered a detached propulsion line in the rear part of the engine compartment, and subsequent tests showed the line was not built to specifications by Stratoflex, a unit of Parker Hannifin.
"It wasn't built to specification as it should have been," said one of the sources. "But there's a very small population of the tubes, and the problem should be fixed soon."
Stratoflex is a subcontractor to engine maker Pratt & Whitney which builds the engines for the single-engine, single-seat fighter jet along with Britain's Rolls-Royce Plc which makes the lift fan for the F-35B model.
A speedy conclusion to the investigation would be good news for the F-35 program, which is racing to complete an aggressive schedule of flight tests this year.
The F-35 program has completed about 34 percent of its planned test flight program, but Lockheed is already building production models of the new warplane.
Lockheed is building three different models of the F-35 fighter jet for the U.S. military and eight countries that helped pay for its development: Britain, Canada, Italy, Turkey, Denmark, the Netherlands, Australia and Norway.
The Pentagon plans to buy 2,443 of the warplanes in coming decades, although many analysts believe U.S. budget constraints and deficits will eventually reduce that overall number.