WASHINGTON — General Electric Aviation on Monday said it and the U.S. Air Force finished testing the firm’s second adaptive engine, which it hopes the military will adopt for the F-35 jet, and is ready to move into the engineering and manufacturing development phase.

In March, GE began testing the prototype XA100 — its offering for the military’s Adaptive Engine Transition Program — at the Arnold Engineering Development Complex on Arnold Air Force Base in Tennessee. This was the second phase of testing for the engine, GE said, and was meant to more closely replicate flight conditions and more precisely measure results than the first phase of tests at GE’s Evendale, Ohio, facility in 2021.

GE said in a release Monday that the completion of testing at the Arnold facility marks the final major milestone of the AETP contract it won in June 2016.

Pratt & Whitney, maker of the F-35′s current F135 engine, received the other AETP contract. Pratt & Whitney calls its in-development engine the XA101.

“This is the culmination of more than a decade of methodical risk reduction and testing GE has completed with the Air Force across three different adaptive cycle engine programs,” David Tweedie, GE’s vice president for advanced combat engine programs, said in the release. “The engine performance data we gathered at AEDC continued to show the XA100′s transformational capability, while also demonstrating a return on substantial Air Force and taxpayer investment.

“We now stand ready to transition to an engineering and manufacturing development program and bring this engine to the field with the F-35 before the end of this decade.”

The Defense Department is considering whether to replace the F-35A’s F135 engine with a new adaptive model, which uses advanced composites and new technologies such as a third stream of air to improve fuel efficiency, thrust, speed, range and heat management. It also includes an adaptive cycle that would allow the engine to adjust to the configuration that would give it the most thrust and efficiency for a given situation.

The Air Force argues that adding more power and better heat management by adding an adaptive engine to the F-35A would help it handle upgrades in years to come.

However, the adaptive engine would also be expensive, with Air Force Secretary Frank Kendall estimating its development and production costs could reach $6 billion.

In a statement to Defense News, Pratt & Whitney said the testing process of its XA101 adaptive engine “remains on track” and on schedule.

Pratt & Whitney reiterated its position that its proposed block upgrade to the F135, which it calls the Enhanced Engine Package, or EEP, would be a better approach for the F-35 than the adaptive engine.

EEP “delivers the fastest, most cost-efficient, lowest-risk path to fully enabled Block 4 capability for all F-35 operators, while saving taxpayers $40 billion in lifecycle costs and building upon a combat-tested architecture with more than 1 million flight hours of dependable operation,” Pratt & Whitney said. “A new engine will cost billions more, introduce unnecessary safety risks, damage alliances with key international partners and is late to need.”

Pratt & Whitney said it is committed to continuing to develop adaptive engine technology, but sees it better suited for the sixth-generation Next Generation Air Dominance family of systems expected in the next decade.

Pratt & Whitney, GE, and three other firms received contracts from the Air Force last month to prototype adaptive engines for next-generation aircraft.

Tweedie said in a June interview that GE had built and tested two full-scale prototypes of the XA100. The initial prototype was first activated in December 2020 at GE’s Evendale facility, and tests followed in early 2021.

The second prototype — the one that recently finished testing at Arnold — underwent its first phase of tests at Evendale from August to November 2021. Last fall’s tests focused on structural and mechanical testing, as well as some performance testing.

In June, Tweedie said the Arnold tests earlier in the spring and then this summer would produce more finetuned data for the engineering and manufacturing development phase, if the program were to take that step.

Kendall said Sept. 7 that the Defense Department needs to soon make a choice on whether to put an adaptive engine into the F-35A, and that he hopes a decision will come as part of the fiscal 2024 budget proposal next year.

“I don’t want to continue to spend money on an engine that we’re not going to develop and take into production,” Kendall said at the Defense News Conference in Arlington, Virginia. “We just need to make a decision, decide what to do and get on with it.”

Stephen Losey is the air warfare reporter for Defense News. He previously covered leadership and personnel issues at Air Force Times, and the Pentagon, special operations and air warfare at Military.com. He has traveled to the Middle East to cover U.S. Air Force operations.

More In Air Warfare