U.S. Air Force Receives Specially Modified Fighter with a Critical Role: The Most Important F-35 in the Fleet

The U.S. Air Force 461st Flight Test Squadron based at Edwards Air Force Base has received a unique specially instrumented F-35A fighter designed to enhance the much delayed testing of new software. The new aircraft is expected to help accelerate efforts to bring the F-35’s software fully up to the Technology Refresh 3 (TR-3) standard, which is critical to keeping up with the latest advances in Chinese fifth generation fighter programs, and eventually facilitating bringing the F-35 up to the Block 4 capability standard in the early-mid 2030. The TR-3 standard was previously expected to be reached around the early 2020, and the Block 4 standard around 2025. In February 2025 the Pentagon’s Director of Operational Test and Evaluation reported that operational testing of TR-3 software on the F-35 was unlikely to commence before 2026, with further delays remaining possible. Delays have worsened despite a significant watering down of the requirements to bring the aircraft to the Block 4 standard.

The issue of delays has been serious enough that in July 2023 the Joint Program Office placed F-35 procurements on hold, with the Pentagon refusing to approve deliveries specifically because TR-3 software had not been fully tested. The fallout for the U.S. Air Force, which was already years behind schedule in bringing the F-35 into service, was particularly serious. Commenting on the importance of the new to accelerating development world, the director of the F-35 Integrated Test Force Lieutenant Colonel Daniel Prudhomme observed: “As the world’s only F-35A capable of evaluating both mission systems and flight sciences, this new asset is key for rapidly fielding advanced capabilities to the warfighter.” “This new aircraft arrives at a crucial time, supporting intensive testing of TR-3 software upgrades and next-generation weapons integration,” he added. While it remains uncertain whether the commissioning of a new testbed aircraft into service will make a significant contribution to addressing the very serious issues affecting the program, the possibility that it does and the extent of the outstanding issues makes testbed aircraft critically important to the program.