The U.S. Department of Defense plans to send Congress this month a multi-billion-dollar upgrade plan for the Lockheed Martin [LMT] F-35 Joint Strike Fighter, the Government Accountability Office (GAO) said Aug. 8.

The report on the Block 4 modernization effort is required by the fiscal year 2017 defense authorization act and was supposed to be submitted to Capitol Hill in March. But due to budget uncertainties and a change in F-35 leadership, the program is reassessing Block 4’s cost, schedule and capabilities, delaying the report’s completion by about five months, the GAO said.

Hill Air Force Base F-35As fly in formation over the Utah Test and Training Range, March 30, 2017. (U.S. Air Force photo/R. Nial Bradshaw)
Hill Air Force Base F-35As fly in formation over the Utah Test and Training Range, March 30, 2017. (U.S. Air Force photo/R. Nial Bradshaw)

The release of the Block 4 request for proposals has also been delayed from the third quarter of FY 2017 to sometime “later in the year,” the congressional watchdog agency added.

Block 4, whose development is expected to cost more than $3.9 billion through 2022, will be a mix of hardware and software updates delivered in four increments. Increments 4.1 and 4.3 will focus on software, while Increments 4.2 and 4.4 will emphasize hardware. A requirements document for the first two increments received approval from the Joint Requirements Oversight Council in April.

The GAO expressed concern that DoD plans to begin buying Block 4 aircraft in its FY 2019 budget request, or more than two years before it finishes developing Increment 4.1. Program officials told the GAO that they are reviewing this “concurrency” issue as part of their Block 4 reassessment.

The GAO also worried that the F-35 likely needs a new, higher-capacity data processor for Increment 4.1 but may not get it until Increment 4.2.

“This poses a risk that the testing and delivery of the first increment of Block 4 capability may not be achievable as planned,” the agency wrote. “As a result, DoD 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. Consequently, Congress will be faced with the challenge of making funding decisions with limited information.”

The GAO made its comments in an eight-page report addressed to the chairmen and ranking members of the four congressional defense panels.