WASHINGTON — The U.S. Air Force is contemplating a controversial proposal to retire its fleet of air superiority F-15C/D Eagles sometime after 2020, but manufacturer Boeing says the service has already put the jets on a path that will keep them in service and relevant into the 2030s.

By replacing the aircraft's longerons — the thin strips of material that make up the skeleton of an aircraft — the Air Force can extend the life of the F-15C/D past 2030 for about $1 million per aircraft, Boeing's vice president of F-15 programs, Steve Parker, said during an April 17 interview.

"So from a taxpayer perspective, it's very cost effective," Parker said. "It's a conservative number. And also from our perspective, at a time when the Air Force is talking about the need to maintain capacity and capability, this maintains capacity and it provides the capability that the Eagle is known for."

While Air Force officials maintain that no final decision has been made about the future of the F-15C/D, Boeing stands to lose millions of dollars in upgrade work if the service decides to shelve its Eagles instead of modernizing them. In turn, the F-15C/D's retirement would be a boon to Lockheed Martin, which could step in to provide upgrades like new radars for F-16s that would replace the Eagle throughout the Air Force's active duty and Air National Guard fleet.

"On any aircraft, particularly when they get older, when you look at them, you have to determine how much is it going to cost and how invasive is it to do modifications that we would need to do to extend its life and to keep it going forward." Lt. Gen. Arnold Bunch, the Air Force’s top uniformed acquisition official, told Defense News earlier this week. "There comes a point with an older aircraft, that if I have to go in and I have to basically take major components out, and it costs me so much money and I’m not gaining service life, well it may not be worth it."

Air Combat Command head Gen. Mike Holmes told Aviation Weekin March that the future of the Eagle hinges on whether the Air Force decides to conduct a service life extension, or SLEP, of the aircraft. That would be an expensive proposition at anywhere from $30 million to $40 million.

But that figure represents the most comprehensive rebuild Boeing could do of the jets, Parker said, noting that the company could do other modifications at a cheaper price point.

"What is referred to in that statement is what we would term to be the most costly potential solution," he said. "If you wanted to almost zero out the life of the airframe, you could go and replace the fuselage, you can go replace the wings. But you would do that if the aircraft was going to go out another 40, 50, 60 years."

Replacing the jet’s longerons is on the other side of the cost spectrum, he added. The Air Force is already installing new longerons, which are tested out to 8,800 hours, in the F-15C/D’s canopy sills during depot maintenance. The work is expected to wrap up in fiscal year 2026.

While the Air Force maintains a couple active F-15C/D squadrons at RAF Lakenheath, England, and Kadena Air Base, Japan, most of the 230 or so Eagles are operated stateside by the Air National Guard for the homeland defense mission. Some service officials — including Lt. Gen. Mark Nowland, the deputy chief of staff for operations and a former F-15C/D pilot —have said an F-16 upgraded with an active electronically scanned array radar could perform that mission.

Parker, however, maintains that replacing the F-15C/D with the F-16, even a modified version, would result in a net loss of capability, particularly for air superiority missions.

"It’s faster, it carries more, it’s got more payload, it’s got more range, it can loiter. If the homeland was to be attacked, you’d want the very best asset going out there and defending," he said.

"When you think about it, when you divest the platform, you’ve also got to think about all of the costs of replacing it. You’ve got to retrain all of your aircrew, all of your maintainers. Why would you potentially replace it with an F-16 with a much smaller AESA radar. Why spend all that money when you’ve already spent [money], for the program of record, [on] the AESA upgrade on the F-15C?" he asked, referencing the APG-63V3 radars that have been installed on some Eagles.

So far the Air Force has not indicated to Boeing that it plans to roll back any of the planned modernization programs for the F-15C/D fleet, including a new electronic warfare suite and computers, Parker said.

Boeing will begin flight testing the Eagle Passive/Active Warning and Survivability System (EPAWSS) electronic warfare system next year, while the Advanced Display Core Processor II mission computer will begin delivering its first systems to the Air Force in the next couple months.

Both upgrades are planned for the F-15C/D and F-15E Strike Eagle fleets, but the retirement of the C and D models would leave Boeing with fewer planned sales of those systems.

Valerie Insinna is Defense News' air warfare reporter. She previously worked the Navy/congressional beats for Defense Daily, which followed almost three years as a staff writer for National Defense Magazine. Prior to that, she worked as an editorial assistant for the Tokyo Shimbun’s Washington bureau.

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