Nine groups, including the Taxpayers Protection Alliance and the Project on Government Oversight (POGO), are questioning the Adaptive Engine Transition Program (AETP) for the Lockheed Martin [LMT] F-35 fighter and urging legislators to reconsider investing in AETP.

“We, the undersigned organizations representing taxpayers across the nation, urge you to proceed with extreme caution when considering proposals to spend more money on the F-35 engine,” according to the groups’ July 12 letter to Congress. “The F-35 program as a whole has already cost American taxpayers an exorbitant amount. It is vital that time and care be taken before making decisions that could add considerably to the bill.”

Other letter signatories include the National Taxpayers Union,  Americans for Tax Reform, Council for Citizens Against Government Waste, Progressive Democrats of America, the Quincy Institute, Women’s Action for New Directions, and the 60 Plus Association.

Pratt & Whitney [RTX] builds the F135 engine for the three variants of the F-35.

The F-35 program has said that the plane will need improved engine capabilities after DoD fields the third increment of Block 4, which is to include dozens of new features, including the ability to carry 16 new weapons.

Since 2016, the U.S. Air Force has funded the AETP, but thus far it appears that an AETP engine will fit on the F-35A and possibly the Navy F-35C, not on the Marine Corps’ F-35B short takeoff and vertical landing variant, as the latter requires an engine that drives the lift-fan system, provides bleed air to the roll-posts, and uses a swivel exhaust duct.

The groups’ July 12 letter said that there may be “a number of unforeseen costs to AETP because of the inability of this proposed new engine in its current envisioned forms to work across all versions of the F-35.”

“The Navy has warned it will not be able to use either of the competing versions of the engine being developed under AETP,” the letter said. “This would either necessitate further changes to the AETP or costly changes to existing naval equipment in the future. Either setback would extend the already-lengthy development timeline for the F-35 and add more costs to the backs of American taxpayers.”

“This will not be the first time lawmakers have had to consider a second engine for the F-35,” the groups said. “During the 2011 National Defense Authorization Act (NDAA) process, some lobbied to have billions added for the F136 engine. Thankfully, experienced military personnel like [then-Air Force Chief of Staff] General Norton Schwartz raised objections, and lawmakers then correctly recognized this proposal as wasteful and hasty.”

The Air Force has estimated a development cost of nearly $6.7 billion for AETP, but the service has not released a breakout of such costs (Defense Daily, June 30).

The Air Force has said that its focus for AETP has been on the Next Generation Air Dominance (NGAD) fighter, not the F-35A, due to what the service has said are significant costs for retrofitting AETP engines on the F-35A.

In fiscal 2018, the Air Force exercised options in the AETP contract for the Next Generation Adaptive Propulsion (NGAP) risk reduction effort for NGAD engine components.

In fiscal 2023, the Air Force requested nearly $354 million for advanced engine development, including $286 million for AETP and nearly $68 million for NGAP. House authorizers recommended boosting AETP by $150 million in fiscal 2023, while House appropriators said that they advised funding the Air Force’s nearly $354 million advanced engine development request but, “at the Air Force’s request,” decreasing AETP funding to $133 million and increasing NGAP to $220 million.

General Electric [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 its proposed XA100 engine for AETP to fit on the F-35B (Defense Daily, June 23). GE said that it plans to submit an interim report to the F-35 JPO before September’s meeting of the JSF Executive Steering Board (JESB) and that the company is to submit a final report by the end of the year.

The House Appropriations Committee’s report on the committee’s fiscal 2023 defense bill said that the F-35 JPO plans to meet with the JESB to brief the office’s Business Case Analysis (BCA) on F-35A engine options “not later than the first quarter of fiscal year 2023.”

The committee wants the Pentagon Director of Cost Assessment and Program Evaluation “to conduct an independent cost estimate and comparative assessment of all propulsion solutions that are the subject of the JPO’s BCA and brief its findings to the congressional defense committees earlier if not later than 60 days following the submission of the president’s fiscal year 2024 budget request, or April 30, 2023.”

The Air Force has told lawmakers that the service plans to award a contract for AETP engineering and manufacturing development by the end of fiscal 2024, if DoD decides to pursue AETP. The Air Force may begin retrofitting F-35As with AETP in fiscal 2027 or earlier.

Pratt & Whitney has participated in AETP with the company’s XA101 engine. The company said it has also been investing internal funds in an Enhanced Engine Package for the company’s F135 engine for all three F-35 variants–a package that Pratt & Whitney said could save tens of billions of dollars in engine life cycle costs and provide the cooling needed for advanced weapons on the fighter by 2027-28 (Defense Daily, Nov. 8, 2021).

In June 2016, Pratt & Whitney and GE each received contracts worth more than $1 billion each for AETP.