Two of three models of Lockheed Martin Corp.’s F-35 jet have a “design flaw” that reduces the expected life of a wing structure to 1,200 hours, which is “significantly less than” the expected 8,000 hours, according to the U.S. Defense Department’s testing office.
The “defective” aluminum beam was detected in November on Air Force and Marine Corps test aircraft after an unrelated bulkhead crack surfaced in the Marine Corps model, the office said. The Air Force plans to buy 1,763 of the 2,443 total in the $382 billion U.S. program, the Marines 371.
The flawed part is the forward root rib, an aluminum beam at the forward-inboard corner of the wing that supports a fuselage fairing panel on the Joint Strike Fighter’s leading edge flap, according to Lockheed.
“Structural analysis predicted” that the root rib will have “less than the desired fatigue life,” Pentagon Director of Operational Test and Evaluation Michael Gilmore said in an e-mail statement. “Its short predicted life relative to the stated requirement is a design flaw,” he said.
The heretofore undisclosed flaw underscores the potential for additional cost growth and schedule delays on the Pentagon’s largest weapons program. Previous problems caused former Secretary of Defense Robert Gates to put the jet into an extended development phase not scheduled to end until 2016, four years later than the original schedule.
Wing Won’t Fail
The issue is one of long-term durability that, were the part not fixed, would add to maintenance and support cost. A preliminary Pentagon estimate already pegs F-35 operating costs at as much as $1 trillion, based on a model used by 107 squadrons at 50 sites through 2065, according to Lockheed.
The F-35 program office and Lockheed Martin have conducted a safety assessment and concluded that a root rib failure would not lead to wing failure, F-35 program spokesman Joseph DellaVedova said in an e-mail.
“This is not considered a serious issue,” DellaVedova said. The program office and Lockheed have developed retrofits and new production improvements designed to extend the beam’s life and correct “durability deficiencies,” he said.
“Resolving durability test findings is a well understood process,” he said. Durability testing is conducted early “to avoid costly sustainment later,” he said.
The Air Force’s principle military deputy for acquisition, Lieutenant General Mark Shackelford, said in an interview today the “unanticipated bill” for the fixes will likely come from program funding.
The root rib must be redesigned for future production aircraft, Gilmore said. Inspection and repair procedures are being created for the existing test and production aircraft, Gilmore said.
DellaVedova said in an e-mail statement that about 30 Air Force and 30 Marine Corps versions will be retrofitted. A new design will be incorporated on the assembly line in the upcoming fifth low-rate production contract. The Navy aircraft carrier version does not have this durability issue, he said.
Lockheed Martin spokeswoman Laurie Quincy said the F-35 program office statement speaks for the company.
Shackelford said “while you don’t want to have that type of discovery, it’s a fact of life when you are building new aircraft.”
The defect “is not serious enough to be a danger of a loss of a wing -- not a catastrophic failure,” said Shackelford, a former F-22 test pilot. “But there will be some flying-hour limit,” on current jets and “inspections to monitor that structural member. That has some implication in terms of our maintenance work on the aircraft.”
Gilmore said “it remains to be seen how disruptive” retrofitting aircraft will be to the ongoing flight test and field operations. “The needed modification is understood to be a difficult and complex process,” Gilmore said.
“Little durability testing has actually been completed; therefore, more discovery is possible,” Gilmore said.
Aircraft produced with the original root rib “must be inspected periodically” and have required repair before approximately 1,000 flight hours, Gilmore said.
Durability testing of the wing area was resumed in May but halted last month for about a week when a crack was discovered in a predicted area of the root rib after about 2,800 hours of testing, DellaVedova said. The test was resumed a week later and is ongoing for completion of 3,000 hours, he said. The crack is being monitored.