Less than two years after a new Pentagon leadership team adopted a new integrated master schedule (IMS) for the F-35 Joint Strike Fighter program—which in 2010 plans was to have been declared operational by now—the latest plan is at risk, according to the Defense Department's chief weapons-tester.

Software required to meet the Marine Corps' limited initial operating capability (IOC) date is already expected to be eight months late relative to the August 2011 IMS, Michael Gilmore, the Pentagon's director of operational test and evaluation (DOT&E) told the Senate defense appropriations subcommittee on June 19. Radar and electro-optical system snags have delayed weapons integration, consuming all the margin built into weapons testing. Buffet and transonic wing-drop “continue to be a concern to achieving operational combat capability.”

The root of the software delays is that the program has been forced to add tests at a rate that more than offsets better-than-scheduled testing performance. The main causes, Gilmore says, are the helmet-mounted display system (HMDS) and regression testing—which ensure that changes have not caused problems in areas previously vetted. Regression testing alone has already forced the addition of 366 test points in 2013.

Flight-testing of Block 2A, the last non-combat software release, started in March 2012 with the goal of finishing in February, but was only 35% complete at the end of May. The Marines' IOC software release, Block 2B, was to be delivered for flight-test in August, according to the IMS, but is now not expected before April 2014, only six months before the due date for completing those tests. These have to be finished before the program can perform an operational evaluation in 2015 that must be completed before the Marine IOC, set for July-December 2015.

Sacrificing Block 2B capabilities to meet the schedule is not an attractive option, Gilmore notes, because even full Block 2B aircraft will “likely need significant support from other (fighters) . . . unless air superiority is somehow otherwise assured and the threat is cooperative.”

The Block 3i configuration, the basis of the Air Force's planned IOC date (August-December 2016) is also under tight schedule pressure, Gilmore explains. It is wedded to significant changes to the radar, and to the electronic-warfare and communications-navigation-identification processors (not just the integrated core processor, as reported earlier). Lot 6 F-35s, which start deliveries in 2014, include this new hardware and cannot fly without 3i software. “Maturing Block 3i hardware and software will be a significant challenge in the next 12 to 18 months,” Gilmore warns.

The DOT&E adds that “the most significant source of uncertainty” regarding what combat capability the JSF will provide in 2018 is that the program has to deliver an operational Block 3i while concurrently developing Block 3F, which is intended to meet the key performance parameters set in 2001.

Lockheed Martin says it is “confident that we are on track to meet the software development schedule” and says that prime software design for Block 3F is 41% complete.

Results of tests on the long-troubled HMDS are “mixed, according to comments from the test pilots,” says Gilmore's report. For instance, software to reduce the effects of jitter have done so—but at the cost of introducing another instability, described as “swimming” of the symbology. The fix to light leakage or “green glow” requires the pilot to perform “fine-tuning adjustments” of display brightness as ambient light changes.

Another threat to schedule is weapons integration, which Gilmore characterizes as “very slow.” Synthetic-aperture radar modes have provided inaccurate coordinates, and the electro-optical targeting system (EOTS) has had difficulty maintaining tracks. These problems had to be remedied before weapons tests could proceed.

Some radar and EOTS issues have been fixed, but all the margin built into the IMS, for both Block 2B and 3F weapons testing, has been used up before a single guided-weapon test has been performed. Gilmore writes: “The final Block 3F weapon integration tests are likely to be completed in late 2017, instead of fall 2016. This will make beginning operational testing of Block 3F in January 2018 a challenge.”

Current weapons-test goals include a guided AIM-120 test in November 2013—dependent on fixing software deficiencies—a GBU-12 laser-guided bomb test in October and a Joint Direct Attack Munition guided test in December.

Buffet and transonic roll-off—wing drop in high-speed turns, associated with asymmetrical movements of shock waves—still affect all variants of the JSF, despite control law changes. The program will conduct flight tests this year to assess the problem, but has now reached a limit on what can be done with control laws, Gilmore reports. Further changes would degrade maneuverability or overload the structure.

Earlier DOT&E reports have been critical of the F-35's ability to tolerate accidental or combat damage, and the new report follows that pattern. Gilmore observes that lightning-tolerance testing is yet to be completed and that even then, the fighter's airframe will have to be inspected after known lightning strikes—including skin penetration—because it does not use lightning-tolerant fasteners, Conventional fasteners were selected to save weight. Lockheed Martin says that inflight lightning protection has been approved and the critical design review is closed, with more tests due later this year. On the ground, the current plan is that ground crews will purge the fuel systems of parked aircraft with nitrogen, repeating this process as often as once every 24 hr.

Gilmore also notes that the prognostic and health monitoring system, currently, is unable to provide timely detection of combat damage to the F-35B lift-fan system, which “might fail catastrophically before the pilot can react” during transition to vertical landing. Lockheed Martin comments that “in the remote chance of a failure, the pilot would auto-eject.”