The head of the Pentagon F-35 Joint Program Office (JPO) said on Dec. 12 he still cannot predict when a software issue that has halted new aircraft deliveries from Lockheed Martin since July will be corrected.

The software for Technology Refresh-3 (TR-3), a $1.6 billion cockpit electronics upgrade, was supposed to be delivered before July, but continued delays caused by discoveries of unstable code during flight testing have pushed back the schedule to April-June of 2024. The JPO is refusing to accept new F-35 deliveries until the TR-3 software is fixed.

But the timing of a resolution to the software problem is complicated by the performance of Lockheed’s ground-based software laboratories, Lt. Gen. Michael Schmidt, the F-35 program executive officer, tells the House Armed Services subcommittee on tactical air and land forces.

“I wish I had all of the solutions in place that prove to me that when I do something in the lab, it’s going to show up that way in the air,” Schmidt says.

The disparity between software stability in Lockheed’s laboratories and the Defense Department’s fleet of F-35 flight test aircraft has prompted new doubts about the program’s ability to meet schedule targets.

“The data tells me [the software problem fix] will be in the middle of spring, but I would have had a more positive answer six months ago of when I thought it would be,” Schmidt explains. “I don’t have a super-solid [sense that] I can guarantee you this [specific] date.”

The TR-3 program includes a new L3Harris integrated core processor, aircraft memory unit and panoramic cockpit display. The electronic upgrade is necessary to enable further upgrades planned for the $16 billion Block 4 upgrade program, including a new Northrop Grumman APG-85 radar for U.S. aircraft and an upgraded BAE Systems ASQ-239 electronic warfare suite.

But the software delay is masking deeper issues with deliveries of the TR-3 hardware, Schmidt said.

Only 21 of the 52 F-35s that would have been ready by the end of December contained all of the required TR-3 hardware, Schmidt says. Two components, which Schmidt did not identify, were the source of a bottleneck in the TR-3 production ramp-up, which threatens the pace of production deliveries and retrofits to F-35s previously delivered.

“If we can get these two components to come up [in production rate], we will catch up quickly, but that’s where we’re at,” Schmidt adds.

Lockheed delivered only 80 of 147-153 F-35s through the end of the third quarter that were expected to be delivered this year due to the software delay issue. If the software delays and the hardware shortage can be resolved, the company hopes to clear the backlog of delayed deliveries next year, as well as deliver all 156 aircraft slated for delivery in 2024.