F-35 program officials acknowledge this risk and note that an updated processor may not be available until the second increment of Block 4, the GAO observed. This poses a risk that the testing and delivery of the first increment of Block 4 capability may not be achievable as planned, it said.
"As a result, DOD [Department of Defense] may be negotiating prices for those aircraft without knowing if or when the more advanced capabilities will be delivered and whether they will function as required," the report warned.
In April 2017, the GAO reported that F-35 acquisition costs alone were estimated at nearly $400 billion and operating and sustainment costs over $1 trillion. Defense Department officials noted that, due to budget uncertainties, they are reassessing key costs, schedules, and capabilities, the report added.