The fiscal 2023 conference measure on the defense authorization bill stipulates that U.S. Comptroller General Gene Dodaro, the head of the Government Accountability Office (GAO), will audit the Pentagon’s business case analysis of engine, power, and thermal management modernization options for the Lockheed Martin [LMT] F-35 fighter.

The F-35 Joint Program Office (JPO) and the Pentagon have been conducting and reviewing that business case analysis.

The Senate version of the bill contained the proposal for the Comptroller General review, and, while the House version did not, the latter did direct the F-35 JPO and DoD to brief the defense authorization committees on the cost-benefit analysis of propulsion and/or thermal power management system upgrades for the F-35.

The House-Senate conference agreement provides that the Comptroller General’s review “should encompass all variants of the F-35, and the review should encompass propulsion, power, and thermal management system upgrades for these aircraft.”

DoD’s fiscal 2024 budget next year may lay out the future engine path for the F-35–whether that be the Pratt & Whitney [RTX] proposed Enhanced Engine Package for the fighter’s existing Pratt & Whitney F135 engine or a new power plant, such as General Electric‘s [GE] proposed XA100 Tri-Variant Adaptive engine.

Technology Refresh 3–supported by the L3Harris [LHX] integrated core processor–is the computer backbone for Block 4, which is to have 88 unique features and to integrate 16 new weapons on the F-35. The F-35 program has said that the fighter will need a new or significantly upgraded engine with improved electrical power and cooling capacity to accommodate the 53 new capabilities slated for F-35 Block 4.

In September, U.S. Air Force Chief of Staff Gen. Charles Q. Brown said that “we’d like to get to a decision [on the engine] this year to get to a point that we’d be able to say which way we’re gonna go, and then that way we could better invest and make sure we’re gonna provide opportunities in the future because there’s an aspect of the various variants of the F-35, which engine is gonna fit, is one thing to think through, and how do we do this, not just for the Air Force, or do we do this just for the Air Force, but also looking at the other services” (Defense Daily, Sept. 20, 2022).