The U.S. Air Force may have to cut purchases of Lockheed Martin’s F-35 by a third if it can’t reduce operations and support costs by as much as 38 percent over a decade, an internal analysis shows.

The shortfall would force the service to subtract 590 of the fighter jets from the 1,763 it plans to order, the Air Force office charged with evaluating the F-35’s impact on operations and budgets said in an assessment obtained by Bloomberg News.

While the Defense Department has said it has gained control over costs for developing and producing a fleet of 2,456 F-35s for the Air Force, Navy and Marine Corps – now projected at $406 billion – the internal analysis underscores the current and looming challenges of maintaining and operating the warplanes.

It may cost as much as $1.1 trillion to keep the F-35s flying and maintained through 2070, according to the current estimate from the Pentagon’s independent cost unit.

A chart in the Air Force analysis, which was completed in December, said the service has “very limited visibility into how” increasing funds going to Lockheed for “contractor support” are spent.

The analysis represents the first public disclosure of the potential impact if support costs aren’t reduced. Using figures developed in 2012, the Air Force faces an annual bill of about $3.8 billion a year that must be cut back over the coming decade.

The Air Force is working with the Pentagon’s F-35 program office to reach the 38 percent reduction in operation and support costs through 2028 from the $38 billion calculated in 2012, spokeswoman Ann Stefanik said.

The long-term support concerns are on top of current F-35 challenges including parts shortages, unavailable aircraft and technical issues that must be resolved as the program ends its 17-year development phase. In September, the F-35 is to begin as much as a year of rigorous combat testing that’s required by law. Successful testing would trigger full-rate production, the most profitable phase for Lockheed, as soon as late 2019.

The F-35 program is accelerating: Congress bankrolled 90 jets, or 20 more than requested, in the spending bill for the current fiscal year.

The U.S. Government Accountability Office said in an October report that “there is little doubt” the F-35 “brings unique capabilities to the American military, but without revising sustainment plans” the military “is at risk of being unable to leverage the capabilities of the aircraft it has recently purchased.”