WASHINGTON -- The Pentagon's chief weapons tester has disclosed that the Lockheed Martin F-35 fighters being used for training at a Florida base have problems: radar that functions intermittently, a helmet displaying flickering images, limited cockpit visibility and prohibitions on flying at night or in bad weather.A 47-page report by Pentagon tester Michael Gilmore provides a snapshot of improvements needed before the aircraft can be declared effective and reliable for combat and suitable for full production, a multibillion-dollar decision for Bethesda, Md.-based Lockheed, the world's largest defense contractor.The F-35 is the Pentagon's priciest weapon system, and the estimated cost for a fleet of 2,443 of the fighters has climbed to $395.7 billion, a 70 percent increase since 2001.The rigorous combat testing that's intended to assess the aircraft's capability won't start for several years and isn't scheduled to be complete until 2019, or about seven years later than planned. Full production could be further delayed by additional problems.Gilmore's report warned that the 65-day preliminary test phase the Air Force completed in November is of limited value. "Little can be learned from evaluating training in a system this immature," he wrote in the Feb. 15 report.But Lockheed agrees with the Air Education and Training Command's decision in late December to start training on the F-35A, the Air Force's version of the joint strike fighter, Lockheed spokesman Michael Rein said by email."Lockheed Martin continues to mature operational and maintenance procedures while refining standard operating and tactical procedures for flying the aircraft," Rein said. "This training is also building a cadre of instructors and line pilots."The F-35's reliability today is "significantly below" the target it should be reaching at 2,500 flight hours, Gilmore wrote.