The F-35 Joint Program Office (JPO) and the Government Accountability Office (GAO) disagree over the schedule and cost of completing the fighter’s long-running development phase. Developmental testing of the F-35 should be completed, the GAO argues, before Congress approves more money for follow-on improvements and advance aircraft parts.

The GAO’s recommendations are contained in an annual report on the F-35 acquisition program the audit and investigative agency released on April 24. The GAO estimates the program will need an additional year (until May 2018) and $1.7 billion to complete developmental testing of the Block 3F software specified when the F-35 system development and demonstration (SDD) phase started in 2001. The JPO estimates that developmental testing of the baseline mission systems software will continue for five months through October and cost $532 million more than current funding—money that Lt. Gen. Christopher Bogdan, the program executive officer, has said will be covered using management reserve and contract savings.

“The development program will be delayed; everybody agrees to that, and it will cost more money,” said Michael Sullivan, who led the GAO study, in a podcast accompanying the report. “We’re more or less saying that they should slow it down and complete the development of the baseline aircraft—that last block of software, before they move on to future investments…Simply put, finish what you started back in 2001.”

The agency recommends the JPO reassess its time and cost estimates for completing software developmental testing, delay starting a so-called Block 4 modernization program and clearly identify to Congress the costs and benefits of a proposed economic order quantities (EOQ) approach to ordering parts. The latter two efforts would cost $600 million and $650 million, respectively, in the Fiscal Year 2018 defense budget.

In a statement attributed to Bogdan, the JPO said the Department of Defense (DOD) has already completed a comprehensive assessment of the time and cost needed to complete SDD phase developmental testing—and that testing remains on track to deliver Block 3F software and finish flight-testing it three or four months later in February 2018.

“We do not agree with the GAO’s assessment that an additional billion dollars will be needed to complete SDD,” the JPO said. “The remaining cost to complete the F-35’s $55 billion development program is estimated to be $2.3 billion—money which was already budgeted for the program.”

The DOD has directed the F-35 program “to maintain the resources necessary” to continue SDD flight testing through May 2018. Should that testing extend beyond the current target date of next February, the JPO said it would hold $100 million of follow-on modernization funding in FY2018 to cover the cost.

The JPO also disagreed that it should postpone issuing a request for proposals (RFP) to industry for the Block 4 modernization effort. According to the statement: “Waiting until developmental testing is fully complete to release the RFP for Block 4 development will introduce undue delay and negatively impact the warfighter’s ability to counter a wide spectrum of current and evolving surface-to-air missile threats, integrated air defense systems, as well as current and emerging advanced fighter threats across 12 mission areas identified in the Block 4 capability development document, which was validated by the Joint Requirements Oversight Council on March 21, 2017.”