(WASHINGTON) -- The military believes it has found the source of the potentially deadly oxygen problem that has plagued America's most expensive fighter jet, the F-22 Raptor, for years, Pentagon spokesperson George Little said on Tuesday.
"I think we have very high confidence that we've identified the issues," Little told reporters, before announcing a long-term plan to lift strict flight restrictions imposed by Defense Secretary Leon Panetta on the $79 billion fleet in May. "This is a very prudent way to ensure that we, in a very careful manner, resume normal flight operations."
The mystery problem with the F-22 Raptor was the subject of an ABC News Nightline investigation, which found that since 2008, F-22 pilots have experienced unexplained symptoms of oxygen deprivation -- including confusion, sluggishness and disorientation -- while at the controls of the $420 million-a-pop jets on more than two dozen occasions. In one instance, a pilot became so disoriented that his plane skimmed treetops before he was able to pull up and save himself.
The Air Force subjected the F-22 to intense scrutiny for years, including a nearly five-month fleet-wide grounding last year, but was unable to solve the problem. When the grounding was lifted, the service awarded the plane's manufacturer, defense contracting giant Lockheed Martin, a nearly $25 million contract in part to help identify the problem, but still no answer was found.
The source of the issue, the Pentagon now says, is believed to be a faulty valve in the high-pressure vest that is worn by the pilots at extreme altitudes -- one that Air Force officials believe is constricting the pilots' ability to breathe.
"To correct the supply issue and reduce the incidence of hypoxia-like events, the Air Force has made two changes to the aircraft's cockpit life support system," Little said. "First, the Air Force will replace a valve in the upper pressure garment vest worn by pilots during high-altitude missions. The valve was causing the vest to inflate and remain inflated under conditions where it was not designed to do so, thereby causing breathing problems for some pilots... Second, the Air Force has increased the volume of air flowing to pilots by removing a filter that was installed to determine whether there were any contaminants present in the oxygen system. Oxygen contamination was ruled out."
The Air Force first ordered its pilots to stop wearing the vests last month, but Air Force spokesperson Lt. Col. Tadd Scholtis told ABC News at the time that while the vests were believed to have contributed to the problem, they were "not believed to be the root cause of the prior incidents."
When asked by a reporter if the new solution could also account for the at least five instances in which the Air Force said ground crews working on the F-22s experienced their own hypoxia-like symptoms, Little said he "did not have specifics" on those incidents.
Still, Gen. Charles Lyon, the head of the team investigating the F-22 problem, made his case in the Pentagon against the so-called G-suit and its valve over the past few days, an Air Force official told ABC News, and Little said that on Friday Air Force Secretary Michael Donley and other top Air Force officials presented the Air Force analysis to Panetta.
"After receiving assurances that these corrective measures would minimize hypoxia-like events in the F-22, the secretary approved the Air Force planned sequence of actions to remove flight restrictions over time," Little said.
The process started on Tuesday, he said, with an order from the Air Force for a squadron of F-22s to be deployed to Kadena Air Base in Japan. The planes will fly there at altitudes that will not require pilots to wear the vests.
The Air Force is still in the process of installing an automatic emergency back-up oxygen system to the planes but that process is not expected to be completed until next spring.
Despite costing an estimated $79 billion, no jet in the entire F-22 fleet -- some 185 planes -- has ever seen combat. From Iraq to Afghanistan to the no-fly zone over Libya, the Air Force said the planes simply weren't necessary.
Copyright 2012 ABC News Radio