February 21, 2014
Credit: U.S. Navy
Cracks on an F-35B’s primary support structure found last year are more extensive than previously thought, triggering a halt in ground-based durability testing until the fourth quarter of this year.
The initial cracks were found on section 496, a primary wing carrythrough bulkhead, last fall, prompting officials to stop the ground-based testing at hour 9,400 during the second life’s worth of use — or second 8,000 hr. of equivalent flight hours — to investigate the issue.
Since then, cracking also has been discovered on adjacent bulkheads, according to Joe Dellavedova, spokesman for the F-35 Joint Program Office. “Subsequent inspection of surrounding structures in light of this discovery found additional cracks in two of the other adjacent bulkheads,” he says.
Because the discoveries were found to occur beyond the first 8,000 hr. of use, the issue is not affecting flight operations for the young F-35B fleet. These issues are also, thus far, limited to the B model that employs a sophisticated lift-fan for vertical takeoff and landing operations for the U.S. Marine Corps. The U.K. and Italy also are expected to buy the F-35B.
Dellavedova says the issue is not expected to jeopardize the Marines’ plans to declare initial operational capability with the F-35B in July 2015.
The Pentagon appears to feel the problem is manageable, if disappointing. “We consider this significant, but by no means catastrophic,” says Pentagon procurement chief Frank Kendall. “Root-cause analysis is still ongoing, however, based on preliminary analysis, a redesign of the affected F-35B structural members will be required. We hope to have modified parts available in time for Lot 9 and we are assessing the impact on Lot 8, the 2014 lot.”
He notes that strengthening will be needed for F-35Bs that already have been fielded.
An improved design for the second 496 bulkhead is being developed and will be ready for testing in March, Dellavedova says. Additionally, “new findings on the adjacent structure have just begun a similar design development, so estimates of when repair parts can be made available and installed are in-work, but we estimate the repairs will support a projected fourth quarter of 2014 durability test restart.”
The section 496 bulkhead is the same structure found in 2010 to have had a crack at the 1,500-hr. mark; this temporarily halted flight testing until a fix was implemented.