WASHINGTON — Lockheed Martin Corp.'s F-35 jet developed cracks in testing of the fighter's durability and wasn't sufficiently reliable in training flights last year, the Pentagon's chief tester found.
On-ground testing of the Air Force and Marine Corps versions of the fighter revealed "significant findings" of cracks on five occasions in fuselage bulkheads, flanges, stiffeners and engine mounts "that will require mitigation plans and may include redesigning parts and additional weight," according to an annual report on major weapons by Michael Gilmore, director of operational testing.
Gilmore has repeatedly raised questions about progress of the $391.2 billion F-35 program, the most expensive U.S. weapons system. This year's report, released Tuesday, may draw particular scrutiny because the Pentagon will propose increasing purchases to 42 planes in fiscal 2015 from the 29 Congress authorized this year.
Lockheed, the top U.S. contractor, drew 16 percent of sales from the F-35 last year. "That number will grow in 2014," Bruce Tanner, chief financial officer for the Bethesda, Md.-based company told reporters last week.
In a full-page discussion of durability testing and cracking, Gilmore disclosed an incident in late September when a bulkhead "severed." He said "analysis and corrective actions" were continuing.
Aircraft based in Florida, Arizona, California and Nevada for pilot training missions continue "to be immature" and rely "heavily on contractor support and workarounds unacceptable in combat operations," Gilmore wrote.
Reliability measures "are all below" target goals for the current stage of development, he said.
The aircraft's weight stabilized last year, with little margin for growth without exceeding contractually binding limits that would jeopardize meeting combat requirements, Gilmore said.
The Air Force model, which will be the most numerous of the 2,443 F-35s planned, was within 341 pounds (155 kilograms) of its 29,030-pound airframe weight requirement as of October. The Marine Corps version was within 202 pounds of its 32,577-pound goal with several years of development left.
"Managing weight growth with such small margins will continue to be a significant program challenge," Gilmore said.
The test report also outlined achievements, finding that flight tests performed by 18 jets to evaluate the aircraft's flying prowess and handling qualities "made the planned progress" and "nearly matched or exceeded" sortie goals through October.
Flights designed to evaluate the aircraft's combat systems and integration of weapons "made little progress and continued to fall behind" its goals, Gilmore said.
He also warned of delays in testing and fielding software for the Marine Corps version, the F-35B, which the service has said it hopes to declare operational by December 2015.
General James Amos, the Marine Corps commandant, said at a Rand conference in Washington's Virginia suburbs today that development of what's known as 2B software "is going better than probably others might have thought."
"It's actually what I would call at this point probably medium risk" as the aircraft approaches initial combat capability, Amos said.
Michael Rein, a Lockheed spokesman, said in an emailed statement that Gilmore's report outlined "a tremendous amount of positive information."
"The F-35 aircraft has flown to every corner of the envelope and is meeting or exceeding expectations in flight performance," Rein said. "The challenges identified are known items and the normal discoveries found in a test program of this size and complexity."
Joe DellaVedova, spokesman for the Pentagon's F-35 program, said in an email that "there were no surprises in the report. All of the issues mentioned are well-known to us, the F-35 international partners and our industry team."
"Although the report is factually accurate, it does not fully highlight the F-35 enterprise's efforts to address and resolve the known technical and program-related challenges," he said.