Air Force officials on Thursday faced pushback from House Armed Services members concerned that the service’s plan to buy upgraded fourth-generation fighters won’t come at the expense of state-of-the-art F-35 jets.

The Air Force’s fiscal 2020 budget request includes $1.1 billion slated to buy eight F-15EXs, with plans to purchase another 136 by 2024. At the same time, the service reduced the number stealthy F-35As to 48, although it later included 12 of the jets on a wish list of items that didn’t make the budget cut.

Over the next five years, the Air Force plans to buy two dozen fewer F-35s than it had planned just last year.

“There was no discussion whatsoever about the F-15EX just a few months ago, but it’s a 40-plus year decision you’re making,” said Rep. Michael R. Turner, R-Ohio, who pressed the Air Force on how such a significant program “comes out of thin air.”

Rep. Donald Norcross, D-N.J., chairman of the subcommittee, likewise called the Air Force’s sudden change of plans a “major shift in thinking.”

“For the last four years, in particular, we’ve been hearing about fifth generation, fifth generation,” Norcross said. “And this year it was dropped on our laps about an F-15 coming into play.”

Lt. Gen. James M. Holmes, commander of Air Combat Command, said the Air Force needs about 2,100 combat aircraft. Since Desert Storm, the service had been replacing 20 aircraft a year, a pace that would update the fleet every 100 years, he said.

“We need more airplanes per year, and we are approaching a crisis point,” he said.

An older version of the fourth-generation fighter, the F-15C, is reaching the end of its service life, and the F-15EX — with its already existing production line — was a logical choice, Holmes said.

Additionally, Saudi Arabia and Qatar have invested in updating the F-15EX’s radar, avionics, electronic warfare and cockpit design, meaning the United States would not have to spend heavily to develop upgrades to the plane’s capabilities, he said.

Turner said he worried that the reduced F-35 purchases in the short term would negatively affect the planned savings that come from a bulk buy of the jets from Lockheed Martin. The F-15s are produced by rival Boeing.

“Each year, if we ramp up, our cost goes down,” Turner said. “If we zigzag … we’re causing our own problems in the delivery of parts and the ability of the production line to continue at a faster pace.”

In December, the Air Force announced it had selected Wright-Patterson Air Force Base, which is in Turner’s district, as the location for the F-35s’ office that oversees support for the program’s expansive supply chain.

“Don’t we need to make a greater commitment to F-35 for it to have the sustainability in production, in supply chain, and in lowering costs?” Turner asked.

Will Roper, the Air Force’s top acquisition official, said the service is working diligently with Lockheed Martin to buy “the max number of planes that the line can produce in a healthy fashion.”

The Air Force is trying to strike the right balance of the F-35′s advanced capabilities with the capacity of older aircraft like the F-15 and A-10 Thunderbolt.

Turner noted that the Air Force wanted to get rid of the A-10, only to have Congress intervene and keep the close-air support specialist in the fleet. Holmes replied that cutting the A-10 was a consequence of tight budgets.

After the hearing, Turner told CQ Roll Call that he wants to hold the Air Force accountable.

“The only way that a decision can be reviewed is if you understand the process under which the decisions were made, what requirements were looked at, what options were looked at, what other alternatives, and in this instance, we don’t have much of that to look at,” he said.