Pentagon acquisition chief Frank Kendall says the cost-per-flying-hour estimate for the F-35A recently provided by the stealthy fighter’s program executive officer to The Netherlands is lower than the official figure that will go next month to Congress.

U.S. Air Force Lt. Gen. Christopher Bogdan told Dutch lawmakers that the flying hour cost for the F-35A would be about 10% higher than the F-16, a sharp reduction from earlier assessments.

“It is with a certain set of assumptions,” Kendall told reporters during a roundtable April 24 at the Pentagon, that Bogdan arrived at that figure. “I’m not sure we want to use that set of assumptions.”

The figure forthcoming to Congress next month, however, still will be lower than that provided in last year’s selected acquisition report (SAR) to Capitol Hill, he says. That report cited the F-35A flying hour cost at $31,900, versus $22,500 for the F-16 C/D.

“That’s going to come down this year. I don’t think that is going to come down as much as Chris Bogdan indicated,” Kendall says, adding that he “doesn’t like the metric very much.”

He says that there are at least six different ways to calculate F-35 cost per flying hour, depending on what assumptions go into the figure. And it can be misleading. If you fly a fleet less — as the F-35 is expected to be used owing to advances in simulators — the per-hour cost goes up. But the overall ownership price may be as much or less than legacy fleets.

“The question that I think matters is what is the cost of ownership?” Kendall says. “What is it going to cost you to have comparable levels of readiness for that aircraft? … And that is going to vary by country.” This depends on how much each operator flies the aircraft, how many spares are procured and what level of skilled maintainers are used for specific tasks, among other things.

But operators are struggling to come up with a total ownership cost figure. The Navy has estimated total ownership cost for 50 years at more than $1 trillion, though F-35 overseers have been hard at work to refine assumptions in an attempt to bring that number down.

Company officials have conceded the cost per flying hour for the F-35 could be higher than legacy fleets the single-engine fighter will replace. But they argue that total ownership price will be lower than all of those fleets — such as the F-18, F-16 and A-10 — combined; this was a selling point for the aircraft in its early days.

Cost per flying hour is just one factor of total ownership cost. Sustainment is the area that Kendall says is the most ripe for opportunities to reduce cost. Development is well under way, with more than 40% of flight testing complete. Though risk is still present, especially in software work, Kendall says he is “cautiously optimistic” about the development portion of the F-35. And production is, for now, fairly well understood based on “actuals,” or numbers gleaned from early production lots, he says.

Kendall’s staff is conducting yet another look at sustainment for the F-35, the latest in a series of reviews on the subject. This is after the Pentagon received feedback from contractors during an industry day. He says that performance-based logistics is being considered for the fleet, which is slated to replace Navy, Marine Corps and Air Force fighters.

Figures for the cost per flying hour of the F-35A, B and C are expected in Congress in about one month when the Pentagon sends its latest SAR to the Hill.