"While the F-35 Lightning II joint strike fighter has returned to limited flying, it will not be appearing at the Farnborough International Airshow in the United Kingdom," Pentagon Press Secretary Navy Rear Admiral John Kirby said during a Pentagon news conference.

The F-35 fleet was grounded July 3 in the wake of a June 23 engine fire on the runway at Eglin Air Force Base, Florida. Navy and Air Force airworthiness authorities approved the F-35’s return to flight yesterday.

The return has a limited flight clearance that includes an engine inspection regimen and restricted flight rules, Kirby said, adding that the limits will remain in place until the root cause of the engine fire is identified and corrected.

While the investigation is not yet complete, “we haven’t seen anything that points to a systemic issue across the fleet with respect to the engine,” the admiral said.

'Disappointed' over Farnborough no-show

Even with the return to flight, US and British officials decided not to send Marine Corps and Royal Air Force F-35B aircraft across the Atlantic to participate in the Farnborough airshow. “This decision was reached after a consultation with senior leaders and airworthiness authorities, despite the decision by airworthiness authorities to clear the aircraft to return to limited flight,” Kirby said.

“While we’re disappointed that we’re not going to be able to participate in the airshow,” he added, “we remain fully committed to the program itself and look forward to future opportunities to showcase its capabilities to allies and to partners.”

Under the rules of the flight resumption, the F-35s are limited to a maximum speed of Mach 0.9 and 18 degrees of angle of attack. They can go from minus 1 G to a 3 G’s, the admiral said. After three hours of flight time, each front fan section of each engine has to be inspected with a borescope. “That was a pretty significant limitation in terms of being able to fly them across the Atlantic,” he added.

This is not the first aircraft to have problems like this, Kirby noted, and it won’t be the last. “New programs often go through these kinds of challenges,” he said. “We’re confident that we’re going to get through this.”

Organisers of the Farnborough International Airshow had earlier said: "Farnborough International Ltd, can finally confirm that the F-35 Lighting II will be appearing at the Farnborough Airshow as part of the aircraft’s international debut, after weeks of speculation."

Costly item

At nearly $400 billion, the new warplane, touted as a technical wonder that will form the core of America's future fighter fleet, is the most expensive weapons program in US history  and officials are eager to reassure foreign partners and potential customers that the warplane remains on course.

But the project has suffered one technical setback after another and the latest problem has turned into a public relations headache, just as the Pentagon planned to stage the plane's coming-out-party at Farnborough.

US officials chose the Farnborough air show as a way of showcasing the plane in a country that committed to the project early and has invested heavily in the fighter.

Apart from the United States and Britain, seven countries are taking part in the program: Australia, Canada, Denmark, Italy, the Netherlands, Norway and Turkey.

Israel has expressed an interest in the Joint Strike Fighter, as has Japan, South Korea and Singapore.

"Serious concerns"

Critics of the plane, which is years behind schedule, have seized on the latest problem as proof that the project is deeply flawed.

One US lawmaker, Jim Moran of Virginia, demanded a briefing on the probe into the fire and said the incident "should raise serious concerns about the viability of the program."

Pentagon officials acknowledge a main cause of the plane's troubles was a decision to start building the jet before testing was finished. As a result, bugs and other technical glitches have forced repeated repairs and redesign work, slowing down production.

Officials and industry executives insist the plane promises to become the ultimate stealth fighter jet, able to evade enemy radar while flying at supersonic speeds. But the plane so far has yet to achieve the level of performance and reliability expected.

(VoR, Reuters)