Four dozen members of Congress are urging top Pentagon officials to invest in next generation propulsion technologies for fighter aircraft.

“We urge DoD to fund adaptive propulsion engineering and manufacturing development in the FY24 budget submission and deliver adaptive technology to the services as quickly as possible,” per an Oct. 7 letter from the members to Defense Secretary Lloyd Austin, Deputy Defense Secretary Kathleen Hicks, and Chairman of the Joint Chiefs of Staff Army Gen. Mark Milley.

“If we do not continue to pursue advanced propulsion systems for our fighter aircraft, we risk opening the door for U.S. adversaries to overtake our advantages in fielded engine technology,” said the letter, spearheaded by Sens. Rob Portman (R-Ohio) and Sherrod Brown (D-Ohio) and Rep. Brad Wenstrup (R-Ohio).

“While we work closely with our NATO Allies and partners to support Ukraine in its fight against Russia’s unprovoked, full-scale invasion in the immediate term, we must also not lose sight of the longer-term threats we face,” the legislators said in the letter. “As the 2022 National Defense Strategy (NDS) lays out, the People’s Republic of China (PRC) is ‘our most consequential strategic competitor and the pacing challenge for the Department.’ As well, we know that we will continue to face persistent threats from Iran, North Korea, foreign terrorist organizations, and more.”

“To support the administration’s Indo-Pacific Strategy, we must continue to develop and field advanced propulsion systems which will enable our servicemembers to fly into the theater of operation, complete their mission and return home safely,” per the letter. “We support the prior funding that the department put forth over the last fifteen years to develop technologies to meet these critical threats and urge your continued support for these advanced propulsion systems, which will fuel additional aircraft capabilities such as powerful radars and infrared sensors.”

The letter comes as DoD prepares its fiscal 2024 budget that may lay out the future engine path for the Lockheed Martin [LMT] F-35 fighter–whether that be a Pratt & Whitney [RTX] proposed Enhanced Engine Package (EEP) 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 (TVA) engine.

While TVA has a degree of commonality with the company’s XA100 design for the U.S. Air Force F-35A, adapting the XA100 engine or a derivative of it for the U.S. Marine Corps’ F-35B short take-off and vertical landing (STOVL) aircraft would require a separate development effort, the F-35 program said last month (Defense Daily, Sept. 28).

General Electric’s GE Aviation subsidiary has its headquarters in Evendale, Ohio outside of Cincinnati.

In all, 13 of 16 Ohio representatives signed the Oct. 7 letter, including Wenstrup and Reps. Michael Turner (R-Ohio),  Marcy Kaptur (D-Ohio), Bob Gibbs (R-Ohio), Steve Chabot (R-Ohio), Tim Ryan (D-Ohio), Troy Balderson (R-Ohio), Warren Davidson (R-Ohio), Bob Latta (R-Ohio), Shontel Brown (D-Ohio), Bill Johnson (R-Ohio), Anthony Gonzalez (R-Ohio), and Mike Carey (R-Ohio).

GE has said that it began working with the F-35 Joint Program Office (JPO) in the fall of last year on evaluating whether GE could alter the proposed XA100 for the U.S. Air Force’s Adaptive Engine Transition Program (AETP) to fit on the F-35B. GE targeted the submission of an interim report to the F-35 JPO before the last  meeting of the JSF Executive Steering Board (JESB) and has said that the company will submit a final report by the end of the year.

The company “performed a study with the F-35 JPO and the AETP program Office to see if the XA100 or a derivative thereof could be adapted to work in the STOVL F-35B,” the F-35 JPO said last month. “The resultant XA100 TVA is based on the current CTOL [conventional take-off and landing] F-35A XA100 and maintains a level of commonality, but is significantly different enough that it would require its own independent EMD.”

The F-35 program and GE declined to disclose the total nor specific projected costs of the independent EMD, but the company did say that adapting the XA100 or a variant of it for the F-35B is viable and that that engine design satisfies user improvement requests for the current engine.

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.

Technology Refresh 3 (TR3)–spurred 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.

Pratt & Whitney has said that the F135 EEP has “ample design margin” to allow for the envisioned Block 4 upgrades for the fighter and that EEP will save $40 billion in lifecycle costs.

It seems unclear whether AETP or EEP are the only options, or whether DoD may pursue an open strategy in which bidders may propose either a new engine or an upgraded one.

Since 2016, the Air Force has funded the AETP.