A crew chief assigned to the 158th Maintenance Group prepares an F-35A Lightning II for departure from the Vermont Air National Guard Base, South Burlington, Vt., Jan. 23, 2020. House Democrats vowed Thursday, April 22, 2021, to fight efforts to hasten the production of F-35 Joint Strike Fighters in next year’s defense budget. (Julie M. Shea/U.S. Air National Guard)

Top House Democrats vowed Thursday to fight efforts to hasten the production of F-35 Joint Strike Fighters in next year’s defense budget amid surging costs to keep America’s most expensive weapons system flying.

“The program's over budget. It fails to deliver on promised capabilities and its mission-capability rates do not even begin to meet the services’ thresholds,” said Rep. John Garamendi, D-Calif., chairman of the House Armed Services Committee’s readiness subpanel. “Don’t expect more money. Do not expect to have more planes purchased than are in the president’s [fiscal year 2022] budget. That’s not going to happen.”

Congress adding additional F-35 purchases to the Pentagon's annual requests has become commonplace in recent years. Since 2015, lawmakers have ordered 98 more of the advanced fighter jets than the Pentagon has requested, even as F-35 units have struggled to keep the jets in their inventories flying — often because of parts shortages.

During a more than four-hour hearing Thursday with officials from the Pentagon and the F-35's primary manufacturers Lockheed-Martin and Pratt & Whiney, Garamendi repeatedly expressed anger over the F-35's long history of problems and blamed newly skyrocketing sustainment costs at least partially on the insistence of Congress to add more planes to the Pentagon’s annual budget. Any lawmakers who suggest such additional F-35 purchases this year, Garamendi said, would be in for “a hell of a fight.”

“And, I don’t propose to lose it,” he said.

The hearing came as the Government Accountability Office, a congressional watchdog, issued a new report on the F-35 program that found the projected sustainment costs for the 2,500 fighters that the Pentagon plans to purchase have increased by some $160 billion to $1.27 trillion during the program’s planned 66-year life, despite several efforts aimed to drive those costs down. The GAO concluded the Air Force, at current projected cost rates, cannot afford the 1,763 F-35s that the service wants by 2036 unless it reduces the yearly cost to operate each plan by 47%, or $3.7 million per aircraft per year.

The GAO found the Pentagon could face an about $7.1 billion budget shortfall in the coming years if those operating and maintenance costs are not addressed.

“We hear rave reviews of the F-35, when it is flying,” said the GAO’s Diana Maurer, who testified Thursday about her findings detailed in the report. “The bottom line here is that services have a plane that they cannot afford to fly the way they want to fly, at least in the long term.”

Maurer agreed with Garamendi’s assertion that Congress’ insistence on purchasing extra F-35s each year is among factors driving up the long-term costs to keep the aircraft flying. She said the extra planes added early to the Pentagon’s inventory “complicates efforts” to address sustainment issues, in part because new parts that could be used to keep existing F-35s flying are instead going to build brand new planes.

“It seems like a self-inflicted wound that we could avoid,” said Rep. Donald Norcross, D-N.J., chairman of the House committee’s subpanel on tactical air and land forces. Norcross joined Garamendi in vowing only to include F-35s requested by the Pentagon in the next budget.

“I want to buy a shiny new one. I love them coming off the line … but the cost is that we can’t get those parts, so you have that shiny new one while the [older] ones are just sitting there” unable to fly, he said. “That’s the trade-off, and … it just seems we can do it better than that.”

While sustainment costs have increased, the GAO also found combat readiness rates for F-35s have improved but remain far behind goals set by the Air Force, Navy and Marine Corps.

The GAO reported Thursday that the F-35s average mission-capable rate — the number of aircraft capable of flying at least one kind of mission — improved from 59% to 69% from 2019 to 2020. But full mission-capable rates remained low across all three services, according to the report.

The Air Force led the way with 54% of its F-35s meeting that standard of full mission capability — defined as a jet capable of flying any kind of mission with which its pilot could be tasked. It was still far below the service’s 72% full mission-capable rate objective, according to the GAO. Full mission-capable rates of F-35s in the Navy and Marine Corps were 7% and 15%, respectively.

The mission-capable rate improvements are “not insignificant,” said Air Force Lt. Gen. Eric Fick, who leads the Pentagon’s F-35 Joint Program Office. “The numbers to me are still unsatisfying, but they’re trending in the right direction.”

Fick backed the F-35 program as vital to U.S. national security, telling lawmakers that despite the aircraft’s well-documented troubles, pilots love flying these fighter jets. The aircraft are more capable than any other fighter jet in the world, he said, arguing they were likely the only option if the United States needed to penetrate air space protected by rival nations’ most advanced air defense systems.

But Fick also said he worried that continued cost programs could cripple the program.

“I see cost as our program’s greatest threat,” he said. “Sustainment cost reduction will continue to be my highest priority.”

dickstein.corey@stripes.com Twitter: @CDicksteinDC