Manufacturing problem likely caused F-35B engine failure: sources

WASHINGTON (Reuters) - Pentagon and industry investigators have pinpointed a manufacturing quality 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, sources familiar with the investigation told Reuters.

Pentagon officials are expected to finalize the finding and the proposed fix at a meeting on Monday, said the sources, who were not authorized to speak publicly. They said the F-35B should be able to resume flights as soon as the "nonconforming" parts supplied by a unit of Parker Hannifin Corp are replaced.

The grounding did not affect the Air Force or Navy versions of the radar-evading new fighter since they do not use the same part.

The Pentagon grounded all 25 F-35B jets on January 18 after a propulsion line associated with the B-model's exhaust system failed just before takeoff during a training flight at Eglin Air Force Base in Florida.

The part in question enables actuator movement for the exhaust system associated with the B-model's engine. Instead of traditional hydraulic fluid, it uses fuel as the operating fluid to reduce weight.

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, a unit of United Technologies Corp, which builds the engines for the single-engine, single-seat fighter jet along with Britain's Rolls-Royce Plc.

No comment was immediately available from Stratoflex.

The speedy conclusion of the investigation is 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.

(Reporting by Andrea Shalal-Esa; Editing by Lisa Von Ahn)