Lawmakers in both chambers continued to press Air Force leadership this week on the service’s decision to include eight F-15EX aircraft in its fiscal year 2020 proposed budget.

Multiple members of the Senate Armed Services Committee from both parties demanded answers from Air Force Secretary Heather Wilson and Chief of Staff Gen. David Goldfein during an April 4 hearing, concerned about its effects on the F-35 Joint Strike Fighter program and its effectiveness on a future battlefield. The F-15EX is built by Boeing [BA] while Lockheed Martin [LMT] manufactures the F-35.

Boeing’s F-15 Advanced Eagle, an upgraded version of the F-15E Strike Eagle. (Photo: Boeing)

Service officials continue to toe the company line that the decision was made in an effort to boost its fighter capacity within the budget numbers it was given, and in order to replace its aging F-15C/D fleet (Defense Daily, Feb. 28).

Goldfein told SASC members that the F15-EX has an expected lifespan of 20,000 hours, which Capital Alpha Partners Analyst Byron Callan noted in a Thursday email is twice the lifespan of other fighters, suggesting these airframes will be in service for decades.

Sen. Tammy Duckworth (D-Ill.) asked whether its longevity could sway the Air Force from buying more F-35s down the line, but Goldfein responded: “If we ever get to a point where we’re trading F-35s for F-15s, that’s a bad choice.”

Sen. Joe Manchin (D-W.Va.) asked about the speed at which the service could stand up simulators and other training equipment for the new F-15EXs, as the expectation is to have them fielded within four years. Goldfein said he is “not concerned at all about the transition,” and in fact, that is one reason the service opted for that particular airframe.

He said earlier in the hearing that choosing the F-15EX allows the Air Force to employ the same maintainers and use the same hangars and other equipment as it is using now for the older models, further driving down cost and speed to fielding.

Callan noted in his email that F-15Cs were made for air superiority, and the EX model is assumed to be made for the same mission. “Unless there is a new longer-range very fast air-to-air missile in the works, we don’t know how effective F-15EXs will be in the 2020s and beyond,” Callan said.

Callan noted that there is an opportunity cost when the Air Force spends funds on the F-15EX when it could otherwise spend them on future air dominance.

The Air Force proposes to procure 80 F-15EX aircraft over the five-year future years defense program (FYDP), while cutting 24 F-35As and reducing its planned budget for Next-Generation Air Dominance (NGAD) by $4 billion, according to FY ’20 documents.

Expect the initial indications of true congressional approval or disapproval to emerge during the House and Senate Armed Services Committee markups, said Roman Schweizer of the Cowen Washington Research Group in a March 28 email to investors.

“To us, it would appear that the Air Force is constraining or reducing fifth- and sixth-gen fighter production and development in favor of continuing fourth-gen production,” Schweizer said. He noted that Pentagon officials have suggested the decision was made at least in part to maintain a strong fighter jet industrial base, while replacing the F-15C with a similar airframe (Defense Daily, March 22).

“Based on recent Boeing foreign and U.S. orders for F-15 (Qatar), F/A-18E/F (Navy) and T-X (Air Force), we assume stable and/or healthy production at Boeing’s St. Louis facility even without the new F-15EX purchases,” Schweizer said. “We find it surprising that looking forward to future fighter programs, the Pentagon would reduce NGAD spending that could help U.S. aerospace primes employ their engineering staff on developing new high-end advanced aircraft.”

Schweizer added that budget documents indicate F-15 purchases would ramp up to 18 per year for about $1.8 billion per year, with the total 80 aircraft costing $7.8 billion. Over the revised five-year plan, the Air Force would be buying 56 more fighters than it could under an F-35-only buy.

Some lawmakers expressed concern this week over the potential impact to Lockheed Martin’s manufacturing line. Rep. Mike Turner (R-Ohio), who serves as ranking member of the House Armed Services Committee (HASC) Strategic Forces Subcommittee, asked Air Force leadership at an April 2 HASC hearing whether reducing the number of planned F-35 buys in this budget would affect future manufacturing capability.

“If we buy 48 aircraft this year and not 60, doesn’t it make it more difficult to buy 70 the next year? And isn’t it absolutely that we lock ourselves into an inability to have flexibility to increase the number of the F-35s by what we do this year?” he said. Turner previously served as ranking member of the HASC Tactical Air and Land Forces Subcommittee.

Wilson said the Air Force has included 12 additional F-35s in its FY ’20 unfunded priorities list, bringing the number up to 60 if Congress funds the full request. She added that Lockheed Martin has confirmed it can produce 60 aircraft this year if necessary.

But Goldfein acknowledged that a smaller production number could stymie future aircraft production, noting, “the larger the jump, the more difficult it would be for industry” to produce a greater number of fighter jets.