(NewsNation) — A new report from the U.S. Government Accountability Office (GAO) found that the Department of Defense needs to improve its oversight and reporting process for spare F-35 aircraft parts that are worth millions of dollars.

F-35 jets, which are used by the U.S. and allied militaries, are the costliest weapons system in the Department of Defense’s history. Overall costs for the F-35 program are estimated to be more than $1.7 trillion over its life cycle.

Spare parts from F-35 jets are not tracked or entered into an accountable property “system of record” that could capture and store real-time changes, the report said. These spare parts include engines, tires, landing gear, as well as smaller parts such as bolts, screws and fasteners.

Out of about 1 million lost parts, worth $85 million, the Defense Department only reviewed the circumstances surrounding 2% of these since 2018, the GAO wrote. Spare parts the government has received and accepted are held at over 50 facilities worldwide.

Although U.S. allies don’t own parts, according to Bloomberg, they are able to tap into the Defense Department’s pool of them.

The reason the Pentagon isn’t accounting for these parts is that their offices and contractors haven’t come to an agreement on if the spare parts for the jet are categorized as government-furnished property, the report stated.

Because of this, the GAO wrote, “the F-35 Joint Program Office will be unable to either gain or maintain accountability over these spare parts and will not have data, such as locations, costs, and quantities, needed for financial reporting or to ensure that government interests are protected.”

The F-35 Joint Program Office, in a statement, said it appreciates the GAO’s look into the program, and the recommendations it provided.

“Although the F-35 JPO concurs with the recommendations, it is important for the American people and our global partners to understand that we know where the vast majority of F-35 spare parts are in the global supply chain,” spokesperson Russell Goemaere said. “At this time, our error rate is around 1%, and while this is considered much better than the government goal of 5%, we will continue to work with the services and our industry partners to improve spare parts accountability and drive readiness for our warfighters.”

The GAO acknowledged that the F-35 Joint Program Office has taken “initial steps” to establish property records, and even spent around $12 million to conduct the inventory.

However, these efforts weren’t enough for the office to be able to provide the cost, total quantity and locations of spare parts in the “global spares pool.” Instead, the office relies on prime contracts’ records for this information, per the report.

To read the full report, as well as recommendations from the GAO, click here.

“The F-35 Joint Program Office is moving out on all fronts to accelerate depot capability and capacity, implement solutions to increase spare parts, and reduce overall sustainment costs,” Goemaere added. “We remain focused and fully committed to developing, delivering and sustaining this fifth-generation weapons system for the warfighters.”