Already months behind schedule, US government auditors now predict the latest technical configuration of the Lockheed Martin F-35 stealth fighter will not be ready for service until 2025.

Airframer Lockheed Martin has for over a year struggled to resolve technical issues hindering flight certification of the Technical Refresh 3 (TR-3) package, which includes new hardware and software meant to substantially improve the jet’s onboard computing power.

Delays in certifying TR-3 systems led the Pentagon to halt most new F-35 deliveries in July 2023. That hold remains in effect, with Lockheed’s aircraft delivery numbers suffering accordingly, with fewer than 100 jets turned over in 2023 and none in the first quarter of this year.

Now, independent auditors at the US Government Accountability Office (GAO) say they do not expect TR-3-configured F-35s to be ready for service until 2025.

Polish F-35A final assembly

Source: Lockheed Martin

Lockheed Martin has assembled more than 1,000 F-35 fighters, but has not delivered a new aircraft since late 2023

The agency released a report on 16 May evaluating the current status of the F-35 programme, including the TR-3 certification process and separate efforts to upgrade the jet’s single engine and onboard power and cooling system.

That report outlines a number of setbacks related to TR-3, including production and quality issues at the sub-contractor providing new integrated core processors, and operating software that still does not function properly.

“These challenges, collectively, will delay the full delivery of TR-3 with new capabilities into 2025,” the GAO says.

That time estimate is not necessarily new, with Lockheed’s chief executive making a similar prediction in April.

Software instability appears to present the most significant issue, with the GAO describing problems with the radar and electronic warfare systems to be “especially prevalent”.

“Some test pilots [are] reporting that they had to reboot their entire radar and electronic warfare systems mid-flight to get them back online,” the report reveals.

Those issues have been compounded by separate problems with the onboard hardware and software that support F-35 data recording, “which has made it more difficult for software engineers to quickly identify the causes of the various glitches”, the GAO notes.

With the TR-3 activity nearly one-year behind the original target completion date of July 2023, and still plagued by significant difficulties, Lockheed now plans to roll out a less-capable interim version of the package, in order to resume F-35 deliveries more quickly.

US Air Force F-35A

Source: US Air Force

The Pentagon is separately pursuing upgrades to the F-35’s Pratt & Whitney F135 engine and Honeywell Power and Thermal Management System

Chief executive James Taiclet revealed the plan for a so-called “combat training-capable” standard in an April earnings call with investors. This “Release 1” version of TR-3 will enable pilots, maintainers and squadrons to begin preparing to use the updated jet operationally once its full software load eventually gains approval.

Taiclet said the company is “highly confident” in being able to being delivering those aircraft in the third quarter of 2024, which begins in July.

Current flight-test activities are using 95% of the Release 1 configuration’s full software load, according to Lockheed, giving cause for optimism.

According to the GAO, the interim Release 1 software will allow the Pentagon’s F-35 programme to resume accepting new aircraft, but not field any new capabilities.

The agency says Lockheed expects to start installing the less-capable software package into aircraft in June, after the conclusion of flight testing. This would support Taiclet’s prediction of a third-quarter resumption to deliveries.

Lockheed has continued to assemble F-35s at its full production rate, despite the lengthy pause in turnovers. Company executives say this will allow them to recover revenue lost during that period.

The airframer has assembled more than 1,000 of the jets, with some 990 delivered.