The previously undisclosed halt in high-stress ground testing involves the F-35B, the Marine Corps version that must withstand short takeoffs and landings on carriers and amphibious warfare vessels, according to an annual report on the F-35 that Defense Department testing chief Michael Gilmore sent to Congress recently. Flight testing wasn't affected.
Development of the F-35, the Pentagon's costliest weapons system, has been marked by delays and cost increases. The Pentagon estimates the total cost for development and production of 2,443 F-35 jets will be $395.7 billion, a 70 percent increase since the initial contract with Bethesda, Md.-based Lockheed Martin was signed in 2001.
Durability testing is intended to stress an airframe, assessing its capability to achieve a projected aircraft lifetime of 8,000 "equivalent flight hours."
Testing for the Marine short-takeoff-and-vertical landing version was progressing this year until last month's halt "after multiple new cracks were found in a bulkhead flange" on the fuselage's underside during an inspection after the equivalent of 7,000 hours of testing, according to the report to Congress. The cracks were confined to that area.
Testing of the F-35B model had been restarted in January 2012 after a 16-month delay caused by the discovery, analysis and repair of a previous crack in the plane's bulkhead. All three models of the F-35 are required to go through ground testing to the equivalent of 16,000 hours of flight.
Analysis of the crack continues to find its root cause, plan corrective actions and determine whether the cracks had been predicted in modeling, according to the report.
Joe DellaVedova, a spokesman for the Pentagon's F-35 program, didn't respond to e-mail and phone requests for comment on the report
Michael Rein, a spokesman for Lockheed Martin, the world's largest defense contractor, said in an e-mail Saturday that "we discovered a crack at 7,000 hours" and " stopped structural testing at that point, identified the causes" and "the changes needed." The ground-test aircraft is checked every 1,000 hours, he said.
"We have implemented the fixes" and "expect to resume static testing shortly, as early as late next week," Rein said.
"This had no impact on flight testing and this is normal engineering development and test work," he said. "This is why we do structural testing in the first place."
Still, the test results "highlight the risks and costs" of the Pentagon's F-35 concurrent-development strategy that produces aircraft while they're still being developed, Gilmore said. The aircraft have two more years of structural testing that may result in more "discoveries," he said.
Frank Kendall, the undersecretary of defense for acquisition, said last year the dual-track approach was "acquisition malpractice."
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