Cause of symptoms in F-22 pilots unknown

WASHINGTON, May 10 (UPI) -- Air Force officials say they have yet to determine the cause of symptoms of oxygen deprivation among F-22 Raptor pilots and those who maintain the planes.

Officials also said they remain unsure why a short-term cough -- which can result from breathing high concentrations of oxygen -- is more common in F-22 pilots than in F-15 and F-16 pilots, Stars and Stripes reported.

The F-22 can fly at higher speeds and much higher altitudes than other fighter planes.

Last May, the Air Force had grounded the Raptors after at least 14 incidents of pilots suffering headaches, nausea, fatigue, difficulty concentrating and other symptoms associated with a lack of oxygen. But the planes were returned to the air in September.

Since then, there have been 11 cases of symptoms associated with oxygen deprivation among F-22 pilots, along with such symptoms among five aircraft maintainers, said Brig. Gen. Daniel Wyman, surgeon general of Air Combat Command. The maintainers had been inside cockpits of planes on the ground and did not use oxygen masks, Wyman said.

Two F-22 pilots said on CBS's "60 Minutes" Sunday they refused to fly the planes after oxygen problems caused them to become disoriented.

The two pilots took their concerns about the planes to Rep. Adam Kinzinger, R-Ill. The Military Whistle-blower Protection Act prohibits reprisals against military personnel who bring concerns to members of Congress.