The US military has slightly relaxed the Lockheed Martin F-35A's range requirements because the effort required to achieve the original specification is not worth the cost, the US Air Force's top uniformed officer told Congress on 6 March.

"The difference between the key performance parameter for distance versus the estimate for performance was five miles [8km]," said USAF Chief of Staff Gen Norton Schwartz during his testimony before the House of Representatives' Committee on Appropriations. "The question to me is: How much do we want to invest in order to recover that five miles margin?"

For the USAF the additional cost to regain the lost combat radius is not worth the money, which is why the Pentagon's Joint Requirements Oversight Council decided to relax the performance demanded for the stealthy fifth-generation fighter. USAF Vice Chief of Staff Gen Philip Breedlove sits on that council.

Lockheed Martin F-35A,

 © Lockheed Martin

"It was a judgement call," Schwartz said. "And not an unreasonable one."

In May 2011, Flightglobal reported that the conventional take-off and landing F-35A's combat radius had dropped to 1,080km, or about 11km short of the requirement. The combat radius for the other two F-35 variants had also declined, but remained above their minimum thresholds.

The range was reduced after Pratt & Whitney diverted more bleed air from the F135 powerplant for cooling purposes. The USAF also accepted new estimates that reduced the F-35A's fuel capacity and added the weight and drag of the Lockheed electro-optical targeting system.

[CORRECTION: Due to an editing error, the original version of the article incorrectly stated the F135 was burning hotter than anticipated.]

Source: Flight International