The problems are far from fixed. But at least some of the U.S. stealth fighters are now allowed to start flying again. The rest are grounded until God knows when.

The U.S. military cleared 20 Joint Strike Fighters to resume flight testing on Thursday, after spending the last two-and-a-half weeks on the tarmac. On August 2, a valve malfunctioned on one plane’s Integrated Power Package; the flaw was deemed serious enough that the entire F-35 fleet was forbidden to fly.

The issue hasn’t been resolved, nor is anyone quite sure how to make things right. “An Air Force Safety Investigation Board continues to review the circumstances that led to the failure,” the F-35 Joint Program Office noted in a statement (.pdf). For now, the military will “monitor” the valve during flights, until someone comes up with a “permanent resolution.”

They better come up with something soon. The JSF is the most expensive, most important weapons program in the Pentagon, projected to eventually make up more than 90 percent of America’s air combat power. The JSF’s Integrated Power Package is “the heart of the power and thermal management system” and “one of the few innovations… that distinguish the F-35 as a technological trailblazer,” according to ace aviation reporter Stephen Trimble.

“Its roughly 200hp gas turbine engine sends power to the starter/generator, which powers on the F-35’s engine, which, in turn, powers up the generator. The IPP then manages the air-cycle cooling system, plus acts an emergency power supply in case both starter/generators happen to fail,” he adds. In other words, the thing has to work in order for the jet to fly safely.

Even more serious is the problem facing the Air Force’s F-22 Raptor, which is supposed to be the world’s most advanced dogfighter. The system that’s supposed to supply pilots with oxygen is instead pumping their lungs with anti-freeze vapors and other toxins. “Pilots flying the F-22 have reported in-flight, physiological events at a rate three times higher than crews from other similar aircraft,” the Air Force noted. Some observers suspect that the oxygen system was responsible for the fatal crash of an F-22 last year.

In January, the Air Force put strict limitations on how high the planes could fly — capping it at 25,000 feet. That’s seven and a half miles below what’s supposed to be the F-22’s ceiling. In May, all 165 of the stealth jets were grounded, and haven’t returned to flight since. The shutdown has gone on so long, some Raptor pilots are starting to run the risk of being disqualified from flying their assigned planes.

It’s unclear when the Raptors will be able to fly again. In the meantime, the Air Force has convened its Scientific Advisory Board to look into the problem; the panel’s final report is “projected for later this fall,” according to a military statement.

“The zero-risk solution is not to fly, and that’s not a long-term option; it’s an inherently dangerous business to fly and fight wars,” SAB executive director Lt. Col. Matthew Zuber notes.

Of course, the $411 million Raptor doesn’t fight any wars. America’s premiere aerial attack plane was kept out of conflicts from Iraq to Afghanistan to Libya. And that was back when it was deemed airworthy.

Photo: USAF