Federal auditors are once again sounding alarms over the Pentagon’s embattled F-35 Joint Strike Fighter, which has soared hundreds of billions of dollars over budget.

Besides being the Defense Department’s most expensive weapons program ever, countless problems with the F-35, including design and systematic issues, have continually pushed back the ready-for-combat date. It is now years behind schedule.

Related: General Defends Embattled $850 Billion F-35 Program

Engine issues are one of the major problems inspectors have flagged. The Government Accountability Office reviewed data from flight tests earlier this month and concluded that the reliability of the F-35’s engine, made by Pratt & Whitney, is “very poor.” That makes the likelihood that the jet will soon be ready for battle even more dubious.

The Marine Corps’ version of the F-35 flew just 47 hours because of engine design issues, instead of the 90 hours it was scheduled to fly, GAO officials told Bloomberg. Likewise, the Air Force and Navy versions of the F-35 flew just 25 hours instead of the 120 hours planned.

The GAO’s findings come just as lawmakers are considering whether to grant the DoD an additional $1.2 billion for the jet engines next year. They’ve already approved roughly $17 billion of the total $67 billion for the F-35’s engines alone. The entire program’s price tag is about $391 billion and counting.

"This means that the engine is failing at a much greater rate and requiring more maintenance than expected," auditors said in the report. "While overall reliability has increased, engine reliability over the last year has remained well below expected levels. Improving the F-35 engine reliability to achieve established goals will likely require more time and resources than originally planned."

Pratt & Whitney disagreed with the GAO’s findings, saying that the auditors didn’t account for the new designs that are being incorporated into production.

Separately, while all that money is being poured into the program, auditors are raising concerns about how well the DoD is managing the massive project. A new report released today by the DoD’s Inspector General slams the Pentagon’s management and oversight of the engines system and says Pratt & Whitney isn’t following all of the Pentagon’s procedures and guidelines — which could be leading to overspending and delays.

Related: How DoD’s $1.5 Trillion F-35 Broke the Air Force

The IG found identified 61 “noncomformities” or violations of federal regulator requirements — and recommended that the DoD implement new guidelines and provide more oversight of the company in charge of the engine development. The Pentagon agreed with some of the auditors recommendations but defended the program, saying it’s still in development.

The report comes just after the House Armed Services Committee launched an “independent look at the engine program” before approving extra funding.

This is just the latest issue with the F-35, which has attracted a barrage of negative media attention for of its endless problems and ballooning price tag — estimated to cost $850 billion over its 55-year lifespan.

Although the jet faces increasing scrutiny, the top official in charge of the program, Air Force Lt. General Christopher Bogdan, told reporters last month that the Marines’ version of the F-35 will be ready for combat by this summer.

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