According to several sources, a few pilots have reportedly refused to fly F-22 Raptor fighter aircraft and requested other assignments as investigators struggle to determine the cause of a mysterious breathing system malfunction bedeviling the jets.
In a media briefing Monday, Gen. Mike Hostage with Air Combat Command, didn't identify the pilots and refused to give a specific number, but said their number is "very small" and said each request would be handled individually.
Eleven unexplained reports have been made over the last four years by pilots who say they experienced symptoms of hypoxia, or oxygen deprivation. In November 2010, a U.S. Air Force pilot stationed at Joint Base Elmendorf-Richardson was killed in an F-22 crash, and hypoxia was believed to be a major factor. Complaints led twice to the fleet's grounding.
Hostage said and investigations are continuing, but the problem has not yet been fully understood.
"We are diligently pursuing a variety of hypotheses to try and understand and characterize the exact circumstances we've been experiencing," he said.
The investigation has not found a "root cause" but is making progress, Hostage said. Investigators are broadening their analysis to look at ground maintainers who have experienced oxygen-related problems when handling the jet.
Read more from CNN, here, more from The Associated Press, here, and still more from the Air Force Times, here.