The Next Great Engine War Was Not What You Thought It Was
In June 2016, the AETP program office awarded two separate $1.01 billion contracts with a period of performance through September 2021 to GE and P&W (Ripple, 2016). The program's goals were to complete the design, manufacture, and ground test of two full-scale, flight-weight, F-35-sized prototype engines. Additionally, the engines were expected to increase the F-35’s range by at least 25%, increase thrust by 10%, double the power management, and improve thermal management compared to the incumbent F135 engine (Hoehn & Parrish, 2022). One of the major design considerations the Air Force chose to implement was intentional incompatibility with the F-35 Short Take-off and Vertical Landing (STOVL) variant. Aircraft engines must be sized to meet an aircraft’s most stressful operational conditions. For the F-35, the STOVL variant drove the F135 design, therefore compromising performance for the F-35A and C variants, a phenomenon referred to in the engine community as the “STOVL compromise” (anonymous personal communication, January 11, 2024). As the program progressed through design, contractual options were awarded to further focus on specific aircraft configurations. Option I was exercised to allow for additional integration and testing for an F-35A design, and Option II was exercised to initiate risk-reduction efforts for future air superiority applications. Over the next few years, the program remained a high-visibility program, with numerous briefings and updates requested by senior Air Force and DoD leadership. However, the program remained without a clear transition path to a platform, a fact of which Congress soon took notice. In the Senate Appropriations Committee–Defense Markup
of the FY 2020 Appropriations Bill, the committee noted that the DoD planned to conclude the AETP program in FY 2021 with ground testing; and that no programs, including the F-35, are signaling a demand for the next-generation engine, or budgeting appropriate resources to transition. The committee expressed frustration that failure to transition into production would constitute a “severely missed
opportunity to capitalize on more than $4 billion” and “open the door to our adversaries to eclipse fielded U.S. engine technology in the coming years” (Department of Defense FY 2020 Appropriations Bill, 2019).
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Defense ARJ , Summer 2025, Vol. 32 No. 2: 104—130
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