Defense Secretary Leon Panetta has ushered the F-35B out of the penalty box, after the short-takeoff-and-vertical-landing (Stovl) version of the stealthy fighter was sidelined for poor performance for more than a year by prior Defense Secretary Robert Gates.

Standing in a hangar in front of BF-4, one of two F-35Bs to conduct testing on the USS Wasp amphibious ship last fall, Panetta spoke to a small audience of government and industry workers on the Joint Strike Fighter test team.

“We now believe that because of your work the Stovl variant is demonstrating the kind of performance and maturity that is in line with the other two variants of JSF,” Panetta said here Jan. 20. “The Stovl variant has made — I believe and all of us believe — sufficient progress so that as of today I am lifting the Stovl probation.”

Gates said last year that if the F-35B development project, which at the time was suffering from major testing problems, did not turn around in two years, he would recommend its termination. But he left office last summer, leaving the issue to be addressed by Panetta.

Gates’s announcement was followed quickly by a multibillion-dollar restructuring designed to reduce the concurrency between the development and production phases of the JSF program. The project also includes the F-35A, designed for conventional takeoff and landing, and the F-35C, designed for use on an aircraft carrier. The restructuring announced early last year also decoupled testing for the F-35B, which at the time was suffering, from the A and C models.

George Little, Panetta’s spokesman, said the secretary’s decision to lift the probation was underpinned by improvements in five key areas: structural shortcomings in the Stovl bulkhead, flutter in the auxiliary inlet door, problems in the lift-fan clutch, unexpected wear and tear on the drive shaft, and heating on the roll-post actuator.

The utility of Stovl aircraft — namely the AV-8B Harrier — in recent operations in Libya and Afghanistan has “made an impression on him,” one defense official said, speaking about Panetta.

Though the B variant has emerged from probation thus far unscathed in development, defense officials are expecting a reduction in the production numbers of F-35s in the fiscal 2013 budget being sent to Congress on Feb. 6. This will extend the production plan and likely drive the per-unit price higher, at least temporarily, until orders go up. Lockheed Martin officials originally said their goal was to produce one fighter a day to reap the benefits of savings with high order numbers.

When the B was put on probation last year, Gates trimmed production of the Stovl version.

The U.S. Marine Corps, which will operate the F-35B, is slated to be the first customer to declare operational use for the aircraft as early as 2016, depending on the pace of testing and training at Eglin AFB, Fla. After the U.K. opted to walk away from the B, Italy is now the only international customer officially planning to buy the aircraft. Nonetheless, Marine Corps Commandant Gen. James Amos said he remains “bullish” on the future of the F-35B.

With a much more productive year of testing in 2011 (following the abysmal performance of the Stovl variant in 2010), the test force is looking ahead to weapons separation trials this year, says Lt. Col. Matt Kelly, F-35 flight operations lead at the Patuxent River testing facility. The team has already conducted flights of the F-35B carrying weapons at subsonic and supersonic speeds. Initial flutter testing with the weapon bay doors open in flight have shown no significant problems, Kelly says. The major step, he says, is to drop weapons for the first time, a milestone expected in the second half of the year. Likely candidates will be the 500-lb. Joint Direct Attack Munition and the AIM-120 and AIM-9X missiles.

Thus far, the F-35B has been flown to Mach 1.4.

Kelly says he also expects to begin testing a redesigned tailhook for the F-35C in the second half of the year. The current design encountered problems last year when officials attempted rolling tests and the tailhook skipped over the wire owing to its weight and a problem with the dampening system. CF-3 will be the first test aircraft to have the new tailhook installed.

After the initial ship trials with the F-35B last fall, the B model is not expected to go to sea until 2013, with the C model following in 2015, Kelly says.

Aircraft BF-4 is now operating the Block 1A software and BF-5 is using the 1B package. Kelly says the Block 2 software, which will be used by the Marine Corps to declare operational capability, is not expected at Patuxent River until late this year.

In addition to having multi-level security, the 1B software will have new voice recognition technology that will allow the pilot to conduct some hands-free operations, such as switching the radio channels and squawking identification codes to air traffic control. Eventually, Kelly says, pilots hope to use the voice recognition technology for such operations as changing multi-function displays or shifting modes in the aircraft.

Meanwhile, officials at Edwards AFB, Calif., where the F-35A test force is located, conducted their first night flight with the conventional aircraft this week.

Flights at Eglin have not yet started, however. And, the aircraft there are now being used only for ground maintenance training.