What a crashed jet means for an F-35 program already thin on test planes

WASHINGTON — Amid delays and cost overruns for key F-35 upgrades, officials have increasingly emphasized the need to tackle a top issue for the Joint Strike Fighter enterprise: a limited and aging testing infrastructure, whose woes could delay or endanger future upgrades to the jet.

And now that a brand new F-35 test jet crashed last week, the stealth fighter’s testing problems could get even worse, fleet numbers shared exclusively with Breaking Defense show.

“Any crash of our military aircraft is of utmost concern. While we know that expanding F-35 test capacity is the first step to fundamental F-35 transformation, this incident exacerbates the already urgent need to expand it,” Rep. Rob Wittman, a Virginia Republican who chairs the House Armed Services tactical air and land forces subcommittee, said in a statement last week. 

As of November, the global fleet relies on just 43 test aircraft. F-35 Joint Program Office spokesman Russ Goemaere declined this week to comment on whether that fleet size has changed since Breaking Defense obtained those figures, but even if the numbers have increased slightly, it remains a tiny fraction of the over 1,000 stealth fighters built to date. Those jets are then divided into two subsets, known as developmental test (DT) and operational test (OT) aircraft.

Within the DT fleet are two different kinds of aircraft. One type is dubbed flight sciences aircraft, which are uniquely instrumented to “conduct specialized test events focused on measuring structural and aerodynamic loads on the air vehicle due to stores, propulsion, or flight control changes,” Goemaere said. The JPO currently operates four flight sciences aircraft, and the 16 other DT jets are used to test mission systems. 

According to Goemaere, the F-35B that crashed last week was en route to Edwards Air Force Base and was planned to add to the DT fleet to support mission systems testing. The jet was relatively fresh off Lockheed’s production line in Fort Worth, Texas before it crashed, having been accepted by the government in September. (The pilot was able to eject.) 

The remaining 23 OT aircraft are operated by the military services. These jets “support testing suitability and effectiveness in an operational environment,” Goemaere said. 

Improving F-35 Test Infrastructure

The F-35, like most large acquisition programs, relies heavily on laboratories to develop features like upgrades. Those are then introduced to the real world on test beds like the F-35B that crashed May 28. 

The problem for program officials is that both parts of that essential infrastructure are lacking. For example, software lab space has recently been prioritized to remedy the fighter’s troubled Technology Refresh 3 (TR-3) overhaul, a decision that the Government Accountability Office (GAO) warned in a May report [PDF] could hamper the fighter’s suite of Block 4 upgrades that need that lab space too. The same issue applies to the program’s limited number of test jets. 

Complicating the issue is that, according to Goemaere, the “bulk” of the current test fleet was built in some of the program’s earliest production lots, meaning that those jets are out of sync with more modern configurations and sometimes more prone to maintenance issues. Testing demands, combined with a lean fleet, means the services sometimes even have to loan their own OT aircraft to the JPO for DT activities. 

Specifically when it comes to flight sciences aircraft, GAO found that “in the past, three of the four testing aircraft have been down for maintenance simultaneously, severely limiting testing.” The program has some workarounds in place, GAO found, though testing demands could increase even more once problems hampering development of new features have been resolved. 

Goemaere agreed the flight sciences fleet must be refreshed, stating that the F-35’s program “most critical need is for flight sciences aircraft.” To that end, the program is eyeing replacements with a handful already under contract. Additionally, an amendment Wittman offered to the draft fiscal 2025 National Defense Authorization Act, which is awaiting a vote by the full House after the committee’s May 22 approval, would enshrine authorization for no fewer than nine new test jets. 

Wittman’s language actually tweaks a similar provision that was included in the FY24 NDAA. Through his amendment, the number of aircraft authorized for procurement would be increased from six to nine and would be acquired in the jet’s production lot 18, as opposed to lot 19. The test jets could additionally be manufactured in the fighter’s conventional takeoff, short takeoff and landing, or carrier-launched variants. 

The legislative language, according to a congressional staffer, is “intentionally open-ended” to enable the JPO to choose whether the aircraft should be manufactured in either a flight sciences or mission systems configuration. In responses to Breaking Defense, the JPO appears poised to procure those jets in the flight sciences configuration. 

That leaves the DT jets used for mission systems testing. According to Goemaere, “the F-35 program continuously evaluates the need for and timing of recapitalizing the development test aircraft fleet.” (The military services are separately responsible for recapitalizing their own OT aircraft.) 

Wittman’s committee is also going after other testing improvements. In a briefing with reporters on May 15, Wittman explained the committee’s decision to cut 10 F-35s from the Pentagon’s requested procurement in FY25 would help redirect funds into an “integrated software laboratory,” making a “digital twin” of the fighter and buying more test beds. In other words, “all those that should have been done years ago and haven’t been done. And that’s why we’re so far behind where we are today.” 

Still, House authorizers may not get their wish. House appropriators unveiled their budget this week, which adds F-35s over the Pentagon’s request instead of cutting them like the HASC outlined. Specific details of House appropriators’ spending legislation is expected to be unveiled shortly. 

It’s unclear how far-reaching the ramifications of last week’s crash will be for the F-35 program. But officials will certainly have to count on one fewer DT jet for an aging fleet. The JPO is “still determining the impact, if any, [the crash] will have on the F-35 program,” according to Goemaere.

For Wittman, however, the impact is clear. 

“This incident will undoubtedly cause a technical setback for F-35 modernization and warrants an extensive and thorough investigation to determine the exact cause of this crash,” he said.