The program manager, Air Force Lt. Gen. Christopher Bogdan, told lawmakers today the issue was his top priority.
"My biggest concern in development is software," Bogdan said in remarks prepared for a Senate Armed Services Committee hearing. "I see more risk to the delivery of Block 3F, our full warfighting capability, by 2017."
That model of the Lockheed Martin Corp.-made aircraft is designed to be equipped with a suite of internal and external weapons, including the GPS-guided Joint Direct Attack Munition, laser-guided Paveway II bomb, Advanced Medium-Range Air-to-Air Missile and infrared Sidewinder missile.
The program office will have a better estimate of the planned delivery date this summer after reviewing at least six months of flight testing data, Bogdan said.
The Joint Strike Fighter is the Pentagon's most expensive weapons acquisition program, estimated to cost almost $400 billion for a total of 2,457 aircraft, according to a 2011 defense acquisition report. It's designed to replace such aircraft as the F-16, A-10, F/A-18 and AV-8B.
The department next year plans to spend $8.4 billion to buy 29 F-35 Lightning IIs, including 19 for the Air Force, six for the Marine Corps and four for the Navy, according to its budget request released earlier this month.
The concerns over software remain despite making a "major shift" in oversight the past year, Bogdan said. That change has resulted in faster software development and integration, reduced coding errors and better collaboration between the program office and Lockheed, he said.
The Bethesda, Maryland-based company and its subcontractors "still need to improve both the speed and quality of software development to be able to catch up from previous software delays," Bogdan said.
The Pentagon's top weapons buyer, Frank Kendall, echoed those comments during a separate briefing with reporters to announce an updated effort to improve how the department buys goods and services. "We still got a fair amount of software to write," he said. "There are some risks there."
The military is about 40 percent through the F-35 test program, Kendall said.
In addition to software, "there are still a few other issues we haven't quite put to bed yet, but I'm feeling cautiously optimistic," he said without elaborating. "I won't say there won't be any additional schedule slips."
The department is working to reduce program expenses by negotiating better terms on production contracts, Kendall said. "I want to keep the pressure on to drive it down as much as we can," he said.
Kendall described sustaining the aircraft as "our biggest opportunity" to find long-term savings. The cost of keeping the F-35 in service for 50 years is estimated at more than $1 trillion and the Pentagon plans to hold competitions for the work.
"We can achieve the greatest results there," he said.