Amy Butler Orlando, Fla., Guy Norris Los Angeles and Bradley Perrett Melbourne, Australia

Countries that have ordered the F-35 are still trying to determine if they can afford to operate the new fighter long-term as a debate over the cost per flying hour for the stealthy aircraft continues between the Pentagon and manufacturer Lockheed Martin. But, as they try to sort out the ownership cost for the aircraft, a grounding of the entire test fleet due to an engine issue has once again brought flight-testing to a halt.

In January, Air Force Chief of Staff Gen. Mark Welsh said his staff and Lockheed Martin were working toward a single cost-per-flying-hour figure for the F-35A. Though the Air Force will be the largest operator of the F-35, its F-35A is also slated for use by 10 partner nations that are also eager to better understand ownership cost before they commit to a fleet size. The company's view of the ownership cost is lower than that of the Air Force, Welsh said: “It was characterized in a different way, a different format.” Air Force officials declined to release Lockheed's and its own numbers, saying they are not finalized. The final number is slated for release in the annual selected acquisition report, which will come out next month.

At issue, Welsh says, is obtaining an “apples-to-apples” comparison between the estimated F-35A cost and the price of operating legacy aircraft, such as the F-16 and A-10, that it will replace. The service needs this to estimate how much more money, if any, F-35 use would entail and if procurement numbers would need to be cut to reduce ownership cost.

Lt. Gen. Burt Field, Air Force deputy chief of staff for operations, plans and programs, said last month that he assumes the F-35 is going to be a “little more expensive” than the F-16 to operate. This contradicts Lockheed Martin's marketing promise that customers could operate the new aircraft more cheaply than legacy fleets across their lives.

An industry official says the company's estimate differs from the service's because the Air Force includes some items the company omits. In aiming for an accurate “apples-to-apples” comparison, Lockheed Martin did not include the cost of operating the electro-optical targeting system or information technology used to support the aircraft, for example, the industry official says. This is because the F-16 cost-per-flying-hour figure lacks data on the cost of operating its targeting pods and supporting computer systems. Also skewing the numbers is that the Air Force's legacy aircraft flying hour accounts are not fully funded, so the cost is below what an optimal value would be. With the F-35 estimate, the service assumes full funding for the accounts.

This is a “work in progress,” the industry source says. “We agree the cost per flying hour will exceed that of the F-16.” But Lockheed expects the anticipated total lifetime cost will be less than that of legacy aircraft, the source adds.

Meanwhile, an investigation by F135 engine manufacturer Pratt & Whitney indicates the fighter program has potentially dodged a bullet. Officials say an analysis of an F135's cracked third-stage low-pressure turbine (LPT) appears to show it was an isolated failure, rather than a recurrence of the more serious high-cycle fatigue design issue that hobbled the $400 billion program in 2007 and 2008. Had the fatigue issue resurfaced, it would have inflicted cost and schedule problems the F-35 can ill afford. The crack was found during a routine inspection of F-35 tail number AF-2 on Feb. 19; the entire F-35 fleet was grounded as a precautionary measure.