Lockheed Martin Corp. and the Pentagon say a fix has been found that should prevent more bulkhead cracks on the Marine Corps version of the F-35 Joint Strike Fighter, the costliest U.S. weapons program.
On-the-ground stress testing may resume as soon as Sept. 30, officials said. It was suspended this past September after inspections found cracks in three of six bulkheads on a plane used for such tests.
The suspension increased scrutiny of the Marines’ F-35B, the most complex of three versions because it is intended to take off like a conventional fighter and land like a helicopter. The Lockheed-built plane, which the U.K. and Italy also are buying, is supposed to be declared combat-ready next year.
“They think they’ve got the root cause,” Frank Kendall, the Pentagon’s chief weapons buyer, said in an interview. “They’ve got a process that they want to implement that they believe will fix the problem for the existing jets.
‘‘It’s going to take a while to certify that process,” he said. “They have reasonably good confidence in it. It’s not certain yet that it’s going to fix the problem.”
The projected $398.6 billion acquisition cost for the F-35 has climbed 71 percent in inflation-adjusted dollars since the Pentagon signed its initial contract with Bethesda, Maryland-based Lockheed in 2001, even as plans were adjusted to buy 409 fewer aircraft.
The bulkhead cracks were described as “a new defect” by Michael Gilmore, the Pentagon’s chief weapons tester, when Bloomberg News disclosed the testing halt in February.
“Government and industry engineers identified multiple factors,” leading to the cracking even though the bulkheads were made to specifications, Joe DellaVedova, spokesman for the Pentagon’s F-35 program office, said in an e-mailed statement. These included “underestimating the effect of corrosion-prevention treatments on fatigue life, resulting in not having enough metal thickness in key locations,” he said.
“Bulkhead manufacturing processes will be modified to accommodate increased metal thickness and to minimize stresses within the final bulkhead,” DellaVedova said.
Lorraine Martin, Lockheed’s F-35 program manager, said in an interview that “we do understand what the stresses were that were impacting the aircraft.”
Lockheed, the largest U.S. contractor, has redesigned the bulkhead “so you’ll never see these cracks” again, she said. The new bulkhead will be installed in aircraft to be made in the ninth production contract that’s scheduled to awarded next year. Retrofit kits will be sent to depots to strengthen the aircraft already delivered, she said.
It’s not yet clear how aircraft to be made under the eighth production contract that’s now under negotiation with Lockheed will benefit from the improvements, Kendall said.
“We are negotiating with Lockheed on how to handle that,” Kendall said. “I’d be reluctant to buy jets that I don’t feel are structurally sound.”
Ground testing stresses an airframe to simulate flight conditions and determine whether a plane can reach its projected lifetime, which in the case of the Marines’ F-35B is 8,000 flying hours.
To provide an extra margin of assurance, the Marine, Air Force and Navy versions of the F-35 are all required to undergo tests for the equivalent of 16,000 flight hours. The Marine version was supposed to complete its second 8,000 hours of testing by the end of this year.
The ground-testing aircraft had accumulated 9,480 hours when testing was stopped.