(CBS News) Pilots flying the U.S. military's most advanced fighter jet, the F-22 Raptor, had been getting sick at the controls, and much of the focus toward finding the cause has been on the plane itself.
Now, however, Air Force investigators say the specialized flight suit pilots wear in the F-22 could be at least partially to blame for the oxygen deprivation experienced in flight.
Officials tell CBS News correspondent David Martin that tests carried out in a flight-simulating centrifuge replicated hypoxia-like conditions for pilots wearing the suits. The link to the suits wasfirst reported by CNN on Wednesday.
As "60 Minutes" reported in May (video), the Raptor - the most expensive fighter ever - has been plagued by a mysterious flaw that causes its pilots to become disoriented while at the controls from a lack of oxygen.
Pilots of the stealth fighter have complained that those oxygen-deficit problems have resulted in pilot dizziness, blackouts and other symptoms.
Martin reported that, according to the Air Force, there have been 22 unexplained cases over the past four years in which pilots experienced symptoms of oxygen deprivation.
The F-22 was grounded last year while engineers searched for something that could be contaminating the cockpit air, but the Air Force returned it to flight, sending the F-22s to the Persian Gulf, without finding the cause.
Now, investigators are zeroing in on a part of the flight suit called the "Combat Edge," which "hampers breathing and causes oxygen loss when combined with a physiological condition that collapses air sacs in the lungs," CNN reports.
The Air Force report is also expected to state that another possible problem for pilots is a condition called acceleration atelectasis, which causes a pilot's lungs to not effectively deliver oxygen to the bloodstream. The extreme effects of g-forces along with the pure oxygen breathed by pilots could lead to the condition.
Following the "60 Minutes" report, Secretary of Defense Leon Panetta limited the flights of the F-22 fighter jet to regions where pilots can quickly land the plane if they experience oxygen problems, and also ordered the investigation into the oxygen deprivation problem. The report detailed above is just the first of the monthly updates expected from the Air Force on the problem.