Pentagon, industry seek answers on issue that grounded F-35B

Pentagon and industry officials worked through the weekend to determine what caused the failure of a fuel line on the Marine Corps version of Lockheed Martin Corp's s F-35 fighter jet that prompted the plane's grounding on Friday.

A spokesman for Pratt & Whitney, a unit of United Technologies Corp that builds the engines for the jets, said those involved included officials from Stratoflex, a unit of Parker Hannifin Corp that built the fuel line.

No comment was immediately available from Stratoflex.

Joe DellaVedova, spokesman for the Pentagon's F-35 program office, said on Tuesday it was too soon to say when the short takeoff and vertical landing (STOVL) model of the radar-evading new jet could return to flight, since the investigation was continuing.

"We'll return the STOVL variant to flight once any causal and contributing factors are understood and mitigated," he said.

The Pentagon's F-35 program office announced the grounding of all 25 F-35B model jets on Friday after a fuel line associated with the B-model's exhaust system failed prior to takeoff during a training flight.

The fuel line in question enables movement of the exhaust system, a weight-saving innovation that replaces traditional hydraulics.

The incident came just days after the Pentagon's director of testing and evaluation released an 18-page report detailing an array of problems which he said underscored the "lack of maturity" of the $396 billion fighter program.

A team of experts first examined the failed part at Eglin Air Force Base in Florida, where the incident occurred during a training flight on January 16, and then headed to the East Hartford, Connecticut plant where Pratt & Whitney builds engines for the jets.

DellaVedova said it was unclear if the incident would have any impact on the busy flight test schedule for the new warplane, but said a recent restructuring of the program had added time to the schedule to address any issues that arose during testing.

"We now have a program that has resiliency built into it," DellaVedova said. "That was the whole point of the rebaselining."

Matthew Bates, spokesman for Pratt & Whitney's military engines division, said investigators worked "diligently" through the holiday weekend, along with officials from Stratoflex.

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 Tim Dobbyn)