Lockheed Martin said Tuesday that several parts on the most complex version of its F-35 Joint Strike Fighter were failing more often than expected, a problem that is slowing flight testing on a model tailored for the Marines. The company's chief executive, Robert J. Stevens, told analysts that the problems had occurred on the version that can take off in short distances and land vertically like a helicopter. Stevens said the defects had reduced the flight tests on that model to 74 so far this year, 21 fewer than planned. He said the company was working with suppliers to fix the problems and thought it could catch up by extending some of the flights. Defense Secretary Robert M. Gates recently revamped the F-35 program and removed the general in charge after delays caused projected costs to soar to $382 billion for 2,457 planes. Stevens said the company's overall performance was improving, with flight tests on the other two versions of the plane ahead of schedule. He reiterated that the company expected to build the next 32 planes for at least 20 percent less than Pentagon estimates. Stevens said the parts that had failed on the version for the Marines included a fan that cools the engine and the hydraulic devices that open air-flow panels to provide the vertical thrust. He said valves, switches and power system components had also been unreliable. Company executives said the problems should not delay delivery of the first planes for the Marines next year. The F-35, intended to evade radar, is the Pentagon's largest program. The other versions are a conventional jet for the Air Force and one that can land on aircraft carriers.
