Last week, leading Democrats on the House Armed Services Committee (HASC) lamented the significant, ongoing problems with the Lockheed Martin [LMT] F-35 nearly 20 years after the company beat Boeing [BA] on October 26, 2001 in winning a contract to execute what has become the costliest acquisition program in Pentagon history–a program expected to pile up more than $1.2 trillion in sustainment costs.

High on the problems list is an availability shortage of the Pratt & Whitney [RTX] F135 engine for the fifth-generation fighter.

“Unscheduled engine removal rates and elevated repair scope for engine power modules are outpacing depot production capacity,” U.S. Air Force Brig. Gen. David Abba, director of the F-35 integration office, told lawmakers on Apr. 22. “As of yesterday, 21 total Air Force aircraft are grounded without a serviceable engine, 15 of which are otherwise flyable.”

In a new report, the Government Accountability Office (GAO) found that “challenges related to F-35 engine sustainment are currently affecting the program and may pose its greatest sustainment risk over the next 10 years.”

“In January 2021 the F-35 Joint Program Office [JPO] projected that the program would have a deficit of approximately 800 engines by 2030 without the implementation of considerable mitigation actions,” GAO said. “A deficit of this size could lead to 43 percent of the total F-35 fleet being grounded in 2030.”

More than 800 F-35s out of a projected fleet of 1,851 in 2030 would need engine repairs, per a GAO analysis of F-35 JPO data. Lockheed Martin said that it has delivered 625 aircraft to date domestically and internationally, including more than 250 U.S. Air Force F-35As.

GAO said that F-35 squadrons have removed engines for unscheduled maintenance–mostly power module repairs–more often than expected. On Air Force F-35As and U.S. Navy F-35Cs, the power module has a fan, power, augmenter, and nozzle, while the U.S. Marine Corps F-35B’s module also has a lift fan for short take-off and vertical landing. The power module, which generates the thrust needed for flight, includes a compressor, combustor, and two turbines.

“Specifically, in 2020 the F-35 Joint Program Office projected 52 power module removals, but it experienced 67,” GAO said in its report. “Second, the F-35 program was able to repair only 43 percent of removed power modules in 2020, thereby resulting in a backlog of power modules needing repair. The program planned for Oklahoma City Air Logistics Complex—a key source of engine repairs—to repair 90 percent of the program’s total of removed power modules in 2020. However, according to program officials, Oklahoma City Air Logistics Complex was able to repair only 23 percent of what the program had originally forecasted for the site in 2020.”

The F-35 program is adding technicians at Oklahoma City Air Logistics Complex at Tinker AFB, Okla. to help address the engine repair backlog with a goal of doubling depot capacity this year and then again next year. In addition, the program plans to bolster spare parts inventories for the engine. That repair backlog was 64 power modules in mid-February.

“Looking forward, it is time to find an [engine] upgrade program,” Matthew Bromberg, the president of military engines for Pratt and Whitney, told legislators on Apr. 22. “Even though the F135 is the most capable fighter engine in production, the Joint Strike Fighter is already placing higher demands on the engine than anticipated. In the near future, air vehicle demands for power and thermal management will exceed engine capability. To support future needs, we just completed a roadmap for a low-cost, low-risk spiral engine upgrade program.”

Because of the engine problems and others, including a nearly $450 million cost overrun in the program’s Tech Refresh 3 upgrade and an F-35 full mission capable rate of 54 percent–18 percent below the goal, HASC Democrats have said that they will not support adding more F-35s than requested in the president’s budget for fiscal 2022. As such, the House Appropriations Committee may follow the lead of the HASC Democrats pledging to rein in F-35 cost overruns, performance shortfalls, and schedule delays.

“I’m going to take a deep breath and try to contain my anger at what’s going on here,” Rep. John Garamendi (D-Calif), chairman of the HASC readiness panel, said in his opening statement at the Apr. 22 hearing on the F-35.

“It seems that the case of this industry solution to many of these problems is simply to ask taxpayers to throw money at the problem,” he said. “That will not happen. The easy days of the past are over. The hard days going forward are that this issue must be resolved, and it’s going to get resolved in the work of this committee this year. So don’t expect more money. Do not expect to have more planes purchased than authorized in the president’s budget. That’s not going to happen.”