WASHINGTON — Choosing to replace the F-35′s engine with a next-generation adaptive model could force the U.S. military to buy 70 fewer of the fighters.

Air Force Secretary Frank Kendall warned of the tough decisions that could come with a change to F-35 propulsion at the Defense News Conference in Arlington, Virginia on Wednesday.

The new propulsion system being developed under the Adaptive Engine Transition Program, most likely for the Air Force’s F-35A, could lead to more power and fuel efficiency for the fighter. The Air Force has said that adding more power to the fighter would help it handle upgrades in years to come.

The price tag to develop and produce AETP could top $6 billion, Kendall has said. And that could lead to a hard tradeoff.

“If you have several hundred F-35s in your inventory, how many more F-35s are you willing to forgo to get the new engine?” Kendall said in a panel at Wednesday’s conference. “It’s an expensive engine. It takes a lot just to do the development — several billion dollars. [That] is, in rough terms, 70 F-35s. So are you prepared to have 70 less F-35s in order to have that engine in the ones that you do have?”

The adaptive engine, versions of which are now being developed by Pratt & Whitney and General Electric Aviation, uses new technologies such as a third stream of air to improve fuel efficiency, thrust, speed, range and heat management.

Kendall said he’s hopeful the Defense Department can make a decision on whether to put an adaptive engine in the F-35A as part of the fiscal 2024 budget, but said that is not yet certain. Kendall said he, Undersecretary of Defense for Acquisition and Sustainment William LaPlante and Deputy Secretary of Defense Kathleen Hicks have discussed whether to go with an adaptive engine.

The Defense Department needs to make a choice one way or the other, Kendall said.

“I don’t want to continue to spend money on an engine that we’re not going to develop and take into production,” he said. “We just need to make a decision, decide what to do, and get on with it.”

AETP is not the only option the defense industry is working on to improve the F-35′s engine, Kendall said. He did not say which program he was referring to, but Pratt & Whitney — the maker of the F-35′s current F135 engine — has been working on a program to modernize the F135 called the Enhanced Engine Program.

Industrial base concern an ‘overstatement’

Kendall downplayed concerns about the health of the adaptive engine industrial base recently raised by the head of the Air Force’s Propulsion Directorate, John Sneden. In a briefing with reporters last month, Sneden said that industrial base was “very thin,” and a decision to not move forward with an adaptive engine in the F-35 could lead to its “collapse.”

Kendall called warnings of potential collapse an “overstatement.”

He said it’s important to keep a viable, competitive market for military engines, and find ways to keep multiple companies in that market so they can push technology forward. That is one of the issues being considered as the military figures out what way to go on AETP, he said.

The Air Force’s recent Next Generation Adaptive Propulsion contract awards to five companies to develop adaptive engine prototypes for its next-generation fighter jets also show the strength of that market’s industrial base, Kendall said. In addition to Pratt & Whitney and GE, the Air Force awarded contracts to Boeing, Lockheed Martin, and Northrop Grumman.

The number of engines that will be produced under the NGAP contract — each company’s deal was worth up to $975 million — will be “relatively modest” compared to the F-35′s needs, Kendall said.

Lessons of Afghanistan withdrawal

Kendall also reflected on the August 2021 evacuation of Kabul at the end of the Afghanistan War, during which airmen evacuated about 124,000 Afghans, Americans and others in a span of two weeks.

As a result of the evacuation, the Air Force learned how to better conduct maintenance and keep aircraft flying during future high-intensity airlift operations in austere locations, Kendall said. Artificial intelligence could play a role in this, he said, by using a form of conditions-based maintenance to track how long various parts have flown on the planes conducting the airlift, and predicting which ones might need to be replaced during the operation so spares can be on hand.

Kendall also said the Air Force learned it needs better tools to plan for such operations to make sure airmen have what they need, how to properly sequence aircraft, and how to handle ground operations. Airmen got the job done last year, he said, but it was very “manpower-intensive,” and artificial intelligence could play a role in future preparations.

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.

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