Handout / U.S. Air Force via Reuters file
An F-22 Raptor fighter jet flies in a training mission during Red Flag 12-3 over the Nevada Test and Training Range.
Updated at 8 p.m. ET: The Air Force this week directed F-22 pilots to stop wearing pressure suit vests during routine flights after tests determined the garments could contribute to ongoing oxygen deprivation problems, NBC News has learned.
A senior U.S. military official said that Air Force investigators “haven’t determined definitively that this is the smoking gun that everyone is looking for” but that “this is a significant development.”
During centrifuge testing at Brooks-City Base in Texas, the Air Force was able to recreate some of the hypoxia-like symptoms that pilots have experienced in the F-22, the official told NBC News.
The testers, from the 711th Human Performance Wing, determined that the upper pressure vests do not always deflate properly, making it hard for the pilots to breathe. When tests were done in a high G environment (high levels of acceleration), some pilots could not get their breath at all, the official said.
The official added that the Air Force will continue testing to ensure they “have this situation squared away.”
Lt. Col. Edward Sholtis, a spokesman for the Air Combat Command, said the upper pressure garment is not "the" cause of physiological incidents and that investigators also are looking at the layering of other Aircrew Flight Equipment as contributing to breathing difficulties.
Senator Mark Warner, D-Va., and Rep. Adam Kinzinger, R-Ill., said Wednesday in a joint statement that the F-22 problems are more widespread than earlier reported.
The Air Force told the lawmakers that through May 31 there were 26.43 hypoxia or hypoxia-like incidents per 100,000 flight hours among F-22 pilots -- a rate at least 10 times higher than any other Air Force aircraft, according to the statement.
They said the equipment test results revealed this week were the result of collaboration they recommended with a Navy dive team in Panama City, Fla.
F-22 troubles were widely publicized in a May “60 Minutes” appearance by Virginia Air National Guard Capt. Joshua Wilson and Maj. Jeremy Gordon, who refused to fly the fighter jet and claimed its oxygen system was poisoning them.
"The safety of these pilots and the communities over which they fly should be everyone's paramount concern," Warner said. "The F-22 program has cost $80 billion so far, but the most expensive fighter jet in the world is useless if we cannot ensure the safety of the pilots who fly it."
“As the nation with the strongest military and the brightest minds in the world, we must make certain that we provide our men and women in uniform with the best equipment possible,” Kinzinger said.
In May, Defense Secretary Leon Panetta ordered the Air Force to restrict F-22 flights because of continuing problems with the Raptor's oxygen system. At least 22 pilots suffered from oxygen deprivation while in flight since April 2008.
Panetta ordered that all F-22 flights remain within a "proximate distance" of an airfield in case a pilot should suffer from a hypoxia event and be forced to land. Some F-22s are deployed to southwest Asia.
Panetta also ordered the Air Force to accelerate installment of a backup oxygen system in all F-22s, a process the Air Force does not expect to begin until December. The Air Force awarded a $19 million contract to Lockheed Martin Corp. to install a backup oxygen system in the F-22 Raptor that it makes.
The aircraft were grounded last year temporarily so the Air Force could study its oxygen system.
The Air Force reports that each of the aircraft costs $143 million. The U.S. Government Accountability Office, however, estimates that each F-22 cost taxpayers $412 million, if upgrades and research and development expenses are included.
Defense Secretary Leon Panetta has ordered all F-22 flights to remain near an airfield in case the pilot suffers from oxygen deprivation due to the aircraft's oxygen system. NBC's Brian Williams reports.
Courtney Kube is NBC News' Pentagon producer. NBC News' Libby Leist contributed to this report.
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