“What we have is a phased approach to removing limitations,” Schwartz said. “We have to go back to the Secretary of Defense and demonstrate the results of the improvements, the tests that we’ve performed, and get his head nod on each sequential.”

He said the risk associated with continued operations would be minimized but not wholly eliminated until the equipment modifications were in place.

Asked why the F-22s were being sent to Japan now, Schwartz said, “There’s an operational requirement and the birds are ready to go.” He gave no further details.

Little said the Air Force would replace a valve in flight suits that had restricted breathing at high altitude and has increased the oxygen supply to pilots by removing a charcoal air filter aimed at trapping contaminants that was actually making it harder for pilots to breathe.

“After receiving assurances that these corrective measures would minimize hypoxia-like events in the F-22, (Defense Secretary Leon Panetta) approved the Air Force planned sequence of actions to remove flight restrictions over time. This process starts today,” Little told reporters.

Senator Mark Warner, a Virginia Democrat, and Representative Adam Kinzinger, an Illinois Republican, said the news was promising, but most safety restrictions should remain in force.

They welcomed news that the Air Force had stopped using the charcoal breathing filters that prompted the two pilots to go public about their concerns, and urged the Air Force to rescind disciplinary actions that were still pending against them.

Air Force officials have said they will afford the pilots the same protections guaranteed to government whistleblowers.

Little said the Air Force would also complete other steps designed to make the planes safer, including installation of a back-up oxygen system.

He said altitude restrictions for F-22s could be lifted as early as the fall after a revamped high-altitude garment had been tested and other improvements and studies completed.