One of the stunning admissions that came out of the US Air
Force Scientific Advisory Board F-22 briefing on 29 March was that the service
had let its aerospace physiology competency atrophy.
Read the full story here: http://www.flightglobal.com/news/articles/usaf-to-rebuild-its-aerospace-physiology-expertise-370521/
They also haven't figured out what's causing the F-22's problems:
The Raptor flies well above the 50,000ft ceiling (by USAF regs) of other fighters like the F-15 and F-16, but unlike pilots flying the high-flying U-2, F-22 pilots don't wear a pressure suit. The USAF issues a waiver to pilots, which allows them to fly up to 60,000ft while wearing the Combat Edge g-suit (60,000ft is the limit due to the Armstrong Line-which is found at an altitude of between 62000ft and 63000ft, where the outside air pressure is so low that water will start to boil at 37°C or 98.6°F) The Combat Edge is ostensibly supposed to act as a partial pressure suit.
However, after years (decades) of enduring spells of decompression sickness (from wearing an actual pressure suit, but astonishingly enough, not having it inflated) from exposure to cabin altitudes of around 29,000 ft, U-2 crews are getting some relief.
The USAF is modifying the U-2 to allow for a lower cabin altitude of between 15,000ft and 16,000ft. It's hoped that will banish decompression sickness from the U-2 community--which happens even though crews undergo elaborate pre-breathing (with pure oxygen and cardio) procedures hours ahead of a flight.
Raptor pilots, however, don't have any of those procedures or a pressure suit... but are exposed to nearly the same kinds of cabin altitudes. Perhaps the U-2 community might have some insight into the Raptor community's woes?