The expected costs to produce and sustain the F-35 Lightning II Joint Strike Fighter in service are “simply unacceptable in this fiscal environment,” according to senior Pentagon officials. Air Force acquisition executive David Van Buren and F-35 Joint Program Office chief Vice Admiral David Venlet told a U.S. Congressional committee hearing this week that their latest cost estimates are credible, after the various recent reviews.

The 31 aircraft recently contracted in low-rate initial production (LRIP) Lot 4 at fixed prices will each cost $111.6 million (F-35A), $109.4 million (F-35B) and $142.9 million (F-35C), they reported. These figures exclude the cost of the F135 engines, which are procured separately from Pratt & Whitney. The latest production prices for these are $15 million each for the F-35A/C versions, and $32 million each for the F-35B STOVL versions.

The Pentagon officials also revealed that the package of 19 F-35A aircraft offered to Israel for delivery beginning in 2015 will cost $2.75 billion.

Buren and Venlet said that after two restructurings over the past year, the F-35 program now had “realistic development and production goals, and a significant reduction in concurrency.” However, they admitted that repairs to the stress cracks of the F-35B rear fuselage bulkhead that were discovered in fatigue testing will require that the 29 STOVL production aircraft already ordered be modified in three different ways, depending on their build state.

Meanwhile, Lockheed Martin officials have made optimistic statements regarding the stress cracks and other problems affecting the F-35B, such as the auxiliary engine air-inlet doors (strengthening needed); the engine driveshaft interface (to be redesigned); and unexpected temperatures at the roll-post actuators and lift-fan clutch.

As for other F-35 development risks rated as high, Van Buren and Venlet mentioned the "pilot vehicle interface” and the helmet-mounted display.

Lockheed has now flown the first two F-35A low-rate initial production aircraft at Fort Worth, Texas. These use the Block 1 software, which integrates sensors and communications, and have demonstrated stable performance to date, according to Van Buren and Venlet. The first six LRIP aircraft will join the 12 development aircraft in flight tests, under the restructuring. Another 10 LRIP aircraft are scheduled to fly this calendar year. But three development aircraft have still not been delivered: one F-35B and two F-35Cs.