WASHINGTON (Reuters) - Seven of 10 F-35 fighter jets built by Lockheed Martin Corp were cleared to resume flight tests this week as government auditors raised questions about the long-term affordability of the program.
The Pentagon's F-35 program director said one Air Force variant of the new radar-evading warplane flew at Edwards Air Force Base in California on Tuesday, but three other planes remained grounded after a dual generator failure and oil leak on one warplane last week.
Vice Admiral David Venlet said there was no doubt that the Joint Strike Fighter program, the Pentagon's biggest acquisition program, had failed to deliver acceptable results in the past. However, he said he was convinced that a major restructuring announced in January would lead to improvement.
"By any measure of progress or performance the F-35 program has not delivered acceptable results," Venlet told the subcommittee on tactical air and land forces of the House Armed Services Committee, saying the new plan was based on a far more realistic assessment of cost, schedule and performance.
"Such a grasp on fundamentals and realism is the distinguishing characteristic that makes this plan different from all before it," Venlet said of the program, which is slated to cost $382 billion over the next decades.
Venlet's office said three newer airplanes would remain grounded until it was clear what caused the generators to fail on board the Air Force variant known as AF-4 on March 9.
An inspection over the weekend found that the generator issue stemmed from a "design artifact" that was unique to a new configuration of the generator, used on the newest planes.
F-35 spokesman Joe DellaVedova said an investigation was continuing into what caused the failure, and said resolving the issue was the program's "highest priority."
He said the impact on the development phase of the program and production operations was being assessed.
Michael Sullivan, director of acquisition research for the Government Accountability Office, told lawmakers that the program was "getting close" to the point where it could reasonably enter production, but it still faced challenges.
He said government auditors viewed the latest restructuring as very comprehensive, but said the program needed continued oversight, citing concerns about software development and a short takeoff variant being built for the Marine Corps.
Sullivan said the Pentagon did not yet know the full impact of the restructuring on procurement costs beyond the five-year budget planner submitted with the fiscal 2012 budget.
"Future funding requirements could be higher than projected and the quantities which are considered affordable by the U.S. and allies, could be reduced, further driving up unit costs," Sullivan said in a report for the subcommittee.
Lockheed is developing the three variants of the F-35 Joint Strike Fighter with eight international partners to replace over 13 different planes now operated by the U.S. Air Force, Navy and Marine Corps and foreign militaries.
Sullivan said the program would require "unprecedented" levels of funding -- almost $11 billion a year through 2035 -- at a time when defense budgets were going to be under increasing pressure, and it would have to compete with many other priorities for funding.
Venlet and Air Force acquisition chief David Van Buren defended the Pentagon's effort to end a second engine being developed for the plane by General Electric Co and Britain's Rolls Royce, while lawmakers argued that the alternate engine would result in longer-term savings.
They also argued that having a second engine would help guard against a catastrophic fleetwide grounding if problems arise with the primary engine, built by Pratt & Whitney, a unit of United Technologies Corp.
(Reporting by Andrea Shalal-Esa; Editing by Richard Chang)