WASHINGTON — As the Air Force increases its F-35 buy rate and more joint strike fighters come online, the question is not if it will begin retiring its legacy combat aircraft, but when.

Air Force leaders hope to have a better answer to that question later this fall, when Air Combat Command head Gen. Mike Holmes and Lt. Gen. Jerry Harris, the deputy chief of staff for strategic plans and requirements, hash out a fighter recapitalization roadmap as part of initial budget planning meetings for fiscal year 2020, Holmes told Defense News in a Sept. 11 interview.

“We’re trying to work to get a fighter recapitalization roadmap that everybody agrees on in the Air Force so that then we can take that on to the Hill … and try to be able to show everyone that we do have a plan for the future,” Holmes said.

The plan would lay out “where their unit would fall out and what the plan is to replace it,” with the ultimate goal of “tak[ing] some of that angst away.”

The Air Force knows it could be facing a political battle as it considers how to best phase out three beloved combat aircraft: the F-16, F-15C/D Eagles and the A-10.

Holmes acknowledged that the situation has changed since the start of the F-35 program when the joint strike fighter was considered to be the eventual replacement of the F-16 and A-10.

“Now that Congress has directed us and we’ve decided to keep some number of A-10s, and now that our F-15 service life is showing some wear and some of the margin is gone there, we want to go back and just look at that combination of A-10s, F-16s of the various blocks and F-15Cs and come up with a plan that maintains the best mix of combat capability as we bring on the F-35,” he said. “At the buy rates that Congress has funded for the F-35, we’re going to be a mixed fourth and fifth gen force for a long time.”

Holmes and Harris have put together two separate fighter recapitalization roadmaps and expect to work through the differences this fall, said Holmes, who would not expound upon his recommendations.

“Frankly I don’t want to get ahead of the chief or the secretary’s decision space by getting too far into the pros and cons of which one you might take next,” he said. “The Air Force is working through that.”

Here’s the state of play of the legacy combat aircraft fleet.

The A-10 Warthog

After years of trying to divest the A-10, The Air Force doubled back on plans to mothball the venerable Warthog, announcing during the FY2018 budget release that it intended to keep the A-10 throughout the next five fiscal years.

[Air Force to cut three A-10 squadrons unless funding for new wings emerges]

However, after Rep. Martha McSally, R-Ariz., a member of the House Armed Services Committee and former A-10 pilot, pressed officials about rumors of retiring some of the fleet, Air Force leaders were forced to clarify their intentions.

The service owns 283 A-10s, and 173 of those planes — about seven squadrons — have recently been re-winged by Boeing. The remaining three squadrons, or 110 Warthogs total, will hit the end of their service life as soon as the early 2020s, at which point the Air Force could get rid of them, Holmes explained to Defense News in June.

The situation has changed a little since then. In the Air Force’s unfunded priorities list, the service included $103 million to restart production of A-10 wings and manufacture four wing sets. Both the House and Senate armed services committees have opted to include that money in their defense authorization bills, although it is yet to be seen whether the appropriations committees — which determine government funding levels — follow suit.

If so, the Air Force will have to issue a request to proposals to industry.

“Having the option to go procure some more wings is a great option no matter where we go or what we do. We understand why Congress would want to do that, and then we’ll work with them on exactly how many,” Holmes said during the Sept. 11 interview. “Frankly, that will affect the vendors on whether they are willing to bid for them or not. People will want to know how many we’re going to do and what the longterm future of a contract is before they go forward.”

Because the Air Force has opted to retain at least a portion of its A-10 fleet, Holmes said the fielding of a direct replacement specifically designed for close air support, or CAS, has become less urgent. Air Combat Command had begun putting together a “wish list” of desired capabilities for a next-generation CAS plane, but discussions had not had not progressed past the very earliest stages.

“We didn’t really get down to the trade part that it takes some acquisition professionals to help with, and then we set it aside when we decided we were going to keep the A-10s for a while,” he said.

The F-15C and F-16

During a congressional panel this March, Maj. Gen. Scott West, the Air Force’s director of current operations and deputy chief of staff for operations, sent shockwaves through the defense community by alluding to the then-unknown proposal working its way through the Air Force that would cull the F-15C/D Eagle fleet, which numbers about 230 planes.

To replace those jets, the Air Force would upgrade F-16s with more advanced active electronically scanned array radars, making them more suited for the homeland defense mission currently performed by the F-15.

The biggest obstacle for keeping the F-15 is the cost of making the modifications needed to prolong its lifespan.

Steve Parker, Boeing’s vice president of F-15 programs, told Defense News in April that the company could extend the life of an F-15C/D to about 2030 by replacing the aircraft’s longerons, or the strips of material that make up the skeleton of an airframe. The price tag for that modification would run about $1 million per aircraft.

Holmes said the Air Force will “probably” do some work to the longerons, but then will need to ascertain whether to extend the life of the F-15C’s wings — the next point of high fatigue on the jet. All said, a comprehensive service life extension could cost upwards of $30 million per aircraft.

“There will be some service life extension that’s required, and we’ll have to decide as an Air Force — not just me, but as an Air Force— how much of that we’re willing to afford,” Holmes said.