HUNTSVILLE, Alabama, Feb 21 (Reuters) - Lockheed Martin Corp must redesign bulkheads on its F-35 fighter jet that developed cracks after extended stress testing, but the issue is not expected to delay the U.S. Marine Corps' plans to start using the plane in combat beginning in 2015, Pentagon and Marine Corps officials said on Friday.
"We consider this significant, but by no means catastrophic," Frank Kendall, the Pentagon's chief weapons buyer, said in a statement. "Root cause analysis is still ongoing, however based on preliminary analysis a redesign of the affected F-35B structural members will be required."
Kendall said the F-35 remained the Pentagon's highest priority conventional warfare program. "Nothing has changed," he said. "There isn't any question about the department's commitment to the F-35."
The latest technical issue involving the $392 billion F-53 fighter program, the Pentagon's most expensive arms development project, arose during on-ground durability testing of the short takeoff, vertical landing (STOVL) version of the plane in September, according to the Pentagon's F-35 program office.
The issue was first flagged in a report on the F-35 program by the Pentagon's chief weapons tester, Michael Gilmore, that also raised concerns about the software development effort for the plane.
Joe DellaVedova, spokesman for the Pentagon's F-35 program office, said cracks were initially found in the airplane's four primary bulkheads in September, but additional cracks appeared during follow-on inspections in January.
The additional cracks were first reported earlier Friday by Bloomberg.
In a joint statement, Lockkheed and the F-35 program office said the issue would not affect flight testing of the planes because the cracks developed at over 9,400 flight hours - well beyond the planned 8,000-hour lifespan that the plane is designed for.
"This discovery does not affect current F-35B flying operations, nor is it expected to impact the U.S. Marine Corps' ability to meet its Initial Operating Capability (IOC) in 2015," the statement said.