Sen. Mark Warner, D-Va., and Rep. Adam Kinzinger, R-Ill., said the Air Force reported about 26 incidents of apparent oxygen deprivation per 100,000 flight hours through May 31. That's a rate at least three times higher than that involving any other Air Force aircraft, they said.
Warner and Kinzinger said that as recently as this week, the Air Force maintained the rate of F-22 oxygen-related problems was "relatively low."
"I don't want to say they're hiding anything, and I don't believe there's a cover-up or anything like that," Kinzinger, a former Air Force pilot, said in a teleconference with journalists. But he said he would like to see the Air Force "just be very open with the American people" about the seriousness of the problem and plans for fixing it.
An Air Force spokesman did not immediately respond to a voice message seeking comment.
The Air Force grounded its F-22s for about four months last year because of the oxygen-deficit problem.
In May, Defense Secretary Leon Panetta ordered new flight restrictions on the F-22 and directed the Air Force to enlist the help of Navy and NASA experts to determine why some pilots continue to experience dizziness and other symptoms while flying.
Warner and Kinzinger said the new information came from the Air Force in response to questions they submitted last month after a CBS "60 Minutes" report featured two F-22 pilots from the Virginia Air National Guard who said that they and other pilots had experienced oxygen deprivation, disorientation and other problems during some flights.
The lawmakers said they are concerned that disciplinary measures are still pending against one of the pilots for going public.
"They should not be penalized for expressing those kinds of concerns," Kinzinger said. He added that 10 others have since come forward to talk about the hypoxia-like symptoms they experienced aboard the F-22.
Warner and Kinzinger also said that in response to one of their questions, the Air Force said an early 2011 survey found that a majority of F-22 pilots did not feel confident with the aircraft's oxygen system.
The Air Force ordered installation of new charcoal filters before returning the F-22 to full operations in September 2011, but that seemed to make matters worse — an outcome verified in testing by The Boeing Corp., which recommended discontinuing their use. The Air Force complied.
Now, attention is directed to an upper pressure vest — part of the survival gear worn by F-22 pilots. Navy tests have shown a high failure rate for the vests, Warner said. But he added it's too early to pin the blame entirely on that equipment.
Kinzinger and Warner said they will continue pressing the Air Force to correct the problem.
"This plane is not going to be part of our national defense if pilots don't feel safe," Warner said.
The lawmakers stopped short of saying the F-22 fleet should be temporarily grounded again and praised Panetta for last month's directive, which said F-22 flights must remain "within proximity of potential landing locations" so that pilots can land quickly if they experience an oxygen-deficit problem.
The F-22, manufactured by Lockheed Martin, is the Air Force's most-prized stealth fighter. It was built to evade radar and capable of flying at faster-than-sound speeds without using afterburners.
The 170-jet fleet is stationed at six U.S. bases: Joint Base Elmendorf-Richardson, Alaska: Joint Base Pearl Harbor-Hickam, Hawaii; Joint Base Langley-Eustis, Va.; Nellis Air Force Base, Nev.; Holloman Air Force Base, N.M.; and Tyndall Air Force Base, Fla.
F-22 pilots are trained at Tyndall. Flight testing is at Edwards Air force Base, Calif., and operational testing and tactics development is performed at Nellis.