The maintainers are mechanics on the F-22's ground crews who sometimes have to be in the cockpit while the jet's engine is doing a ground run. "The maintainers, when they are doing their ground run, are not on the mask, they are in the cockpit," Wyman said. The problem with maintainers getting sick while on the ground throws a wrench into some of the theories about why at least 25 pilots have suffered hypoxia symptoms. The Air Force experts trying to figure out the cause of the problem have pointed out that the F-22 flies higher and faster than its predecessors, the F-15 and F-16.

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References:
-http://www.newsforum.com/technology/100385-f-22-stealth-fighter-cover-up.html
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