The F-35's flight plan appears to have delays written all over it. A previously unreleased memo from Michael Gilmore, the Department of Defense's director for Operational Test and Evaluation (OT&E), details a list of problems that will likely hold up the testing of the final configuration of the aircraft—and will mean the "Block 2B" aircraft now being delivered to the Marine Corps soon will continue to be full of software bugs for years to come. But officials with the F-35's Joint Program Office (JPO) have downplayed the seriousness of Gilmore's concerns, with one military member of the office taking to the Facebook page of a defense publication to call the memo "whining."

The concerns center largely on testing of software components—many of which the JPO has deferred to keep the program close to its schedule, and which JPO leadership has suggested would be a waste of time and money to fix now—since they are in interim releases of the F-35's systems and an entirely new set of software will be completed for the final version of the F-35. But with the Marine Corps and Air Force scheduled to fly as many as five F-35A and F-35B aircraft at the Farnborough International Air Show this summer, and production of the aircraft ramping up, so much uncertainty about the software could lead to even more complications down the road—particularly as weapons systems are added to the aircraft.

"The current 'official schedule' to complete full development and testing of all Block 3F capabilities by 31 July 31, 2017 is not realistic," Gilmore wrote in the memo dated from December, which was first obtained by Aviation Week. Making that schedule would require dropping "a significant number of currently planned test points, tripling the rate at which weapons delivery events have historically been conducted, and deferring resolution of significant operational deficiencies to Block 4"—a software upgrade the aircraft won't see until at least 2021.

Of particular concern to Gilmore was the F-35's "Autonomic Logistics Information System" (ALIS), which he said "continues to struggle in development with deferred requirements, late and incomplete deliveries, high manpower requirements, multiple deficiencies requiring work-arounds, and a complex architecture with likely (but largely untested) cyber deficiencies." ALIS is a system that spans from the aircraft itself to the entire supply chain for its maintenance and repair parts, and it includes portable computing gear required to check if the right parts are installed properly before flight. The software is still a work in progress, and testing of potential security vulnerabilities—which could potentially keep aircraft from being able to take off—has largely been deferred for now while Lockheed Martin and the JPO focus on getting the software to actually work as intended.

The Marine Corps' F-35B aircraft are being delivered with Block 2B software, which Gilmore said has "hundreds of unresolved deficiencies." And those problems have compounded in Block 3F software. That's because the first round of Block 3 was created by "re-hosting the immature Block 2B software…into new processors to create Block 3i," the initial release for the code, Gilmore noted. This led to "avionics instabilities and other new problems, resulting in poor performance during developmental testing."

And rather than fix Block 3i, the JPO made a "schedule driven decision," Gilmore said, to throw the final features for Block 3 on top of the buggy code to create Block 3F—the software that will be installed in full-rate production F-35s. The final release of Block 3F is scheduled for the middle of this year.