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.

The fix to the section 496 bulkhead is expected to weight less than 2 lb.; officials have not yet said how much weight the improvements for the other two bulkheads may require.

Despite this problem with the B model, Air Force Chief of Staff Gen. Mark Welsh, who is buying the preponderance of F-35As to be built, is “feeling pretty darn good about this program,” he told reporters during a press conference following the annual Air Force Association Air Warfare Symposium here Feb. 21.

Though there have been repeated delays by prime contractor Lockheed Martin in developing software to operate the single-engine, stealthy fighter, Welsh says work is “on track for [initial operational capability]” for the Air Force in December 2016 as planned. “Everyone is concerned about getting the mission software in the airframe,” he said. “I think we will have the software in the airplane [and] we will be ready for IOC.”

The main complaint from maintainers at Eglin AFB, Fla., where pilot and maintainer training is taking place, is that crews cannot turn the jets around fast enough, so repair and checkout for missions takes longer than planned. “There are some frustrations out there,” said Debra Lee James, incoming secretary of the Air Force.

“We have to start transitioning from the test mentality of flight line maintenance to the operational mentality of flight line maintenance,” Welsh said, noting this frustration is more pronounced for the F-35 than previous systems largely because of the program’s concurrent development and fielding activities.

Testing of the 2B software, needed by the Marines and Air Force for IOC, is slated to wrap up this year, says Lorraine Martin, executive vice president of F-35 for Lockheed Martin. Testing is also expected this year for the new 3i hardware, which will be used by the Air Force for its IOC aircraft, she said.

Additionally, the F-35 joint program office has begun design reviews for the Automated Information Logistics System (ALIS) SOU V2 hardware. It is a version of the ALIS hardware needed to conduct mission planning and maintenance tasks on the F-35. The ALIS hardware now being used is housed on large server racks; the Marines require a smaller system to operate on amphibious ships.

Martin says the SOU V2 hardware will be ready for the 2015 IOC, and it is likely to be adopted by the other two services, as well.

Developmental testing of a new helmet design, with an improved night-vision camera, is also scheduled to start on the F-35 in August, she says. This so-called Gen 3 helmet is needed for conducting night operations and addressing jitter issues at during high buffet maneuvers.