A full-year delay poses a risk to the U.S. Navy’s timeline to declare initial operating capability (IOC) on its F-35C carrier variant and the program’s full-rate production decision planned for April 2019, the government watchdog wrote in an April report. GAO urged the Pentagon to finish development before making “significant new investments” in the aircraft. 
GAO’s estimate is a significant departure from the F-35 Joint Program Office (JPO). The JPO estimates development will be delayed just five months, wrapping up in October 2017, and require only $530 million extra.
The JPO took issue with the GAO’s estimate for the cost and timeline of the F-35 development program.
“The Department of Defense (DOD) already completed a comprehensive assessment of the cost and time needed to complete developmental testing in the System Development and Demonstration (SDD) phase, and so far the testing remains on track to complete in February 2018. This assessment considered historical data and the recommendations from multiple DOD organizations,” according to Program Executive Officer Lt. Gen. Christopher Bogdan. “As the SDD phase further winds down during 2017, the DOD will continue to reassess the assumptions and decisions made, and communicate any necessary adjustments relative to both cost and time needed to compete developmental testing.”
The schedule will not impact Navy IOC or other U.S. and international operational milestones, Bogdan stressed.
The latest cost overrun on Lockheed Martin’s controversial fighter is driven primarily by software challenges and “cascading” testing delays, the GAO says. Lockheed has struggled for years to straighten out recurring problems with the F-35’s complex software. Developmental test pilots flying the different iterations of F-35 software loads experienced frequent glitches during which the aircraft’s systems shut down and needed to be rebooted, both during flight and on the ground. Although Lockheed engineers resolved the problem for the 3i software—the version the U.S. Air Force used to declared initial operating capability in 2016—the problem recurred with the latest and final software, 3f. 
Lockheed officials say they are making progress resolving the issues with Block 3f, the version needed for final warfighting capability. Thanks to Lockheed engineers, these anomalies are now only happening about once every 15 hr., Orlando Carvalho, executive vice president for aeronautics, told Aviation Week in March.
But the problem has been compounded over time, with delays in completing one iteration of software leading to a domino effect on the next. DOD will be challenged to make up for this lost time, GAO warned. The watchdog estimates developmental testing could be as much as 12 months late, delaying the start of the F-35’s final test phase, known as initial operating test and evaluation.
GAO recommended the Pentagon use historical data to reassess the cost to complete F-35 development, complete Block 3f testing before soliciting contractor proposals for follow-on development, and present to Congress the cost and benefits associated with procuring economic order quantities of parts.