G-induced Loss Of Consciousness (abbreviated as G-LOC) is a term generally used in aerospace physiology to describe a loss of consciousness occurring from excessive and sustained g-forces draining blood away from the brain causing cerebral hypoxia. The condition is most likely to affect pilots of high-performance fighter and aerobatic aircraft or astronauts but is possible on some extreme amusement park rides.
G-LOC incidents have caused fatal accidents in high performance aircraft capable of sustaining high g for extended periods. High-G training for pilots of high-performance aircraft or spacecraft often includes ground training for G-LOC in special centrifuges, with some profiles exposing pilots to 9 Gs for a sustained period.
Nevertheless, only a few fighter pilots have experienced G-LOC incidents.
Sustaining 8.5/9G’s for more than a minute in a mock dogfight
Shari Williams, former USAF F-15 Eagle aviatrix, recalls on Quora;
‘Most fighter pilots have “greyed out” (loss of all color vision), less have blacked out (you can see nothing but are still conscious and can hear and function, all be it blind). And a few have lost conscious. Of those that have many have G-LOC’ed (G induced loss of conscious), some have died, some have ejected and lived and some recovered and flew home. If you G-LOC you are grounded and subjected to a physical exam, a few centrifuge rides and a dual flight before you go out single seat.
‘I remember fighting a contemporary at Kadena, we were in clean Eagles at 5000′, above the ocean, lightweight and sustaining 8.5/9G’s for well more than a minute. Neither of us would give up. I remember slowly going from color to grey to black. I could hear, I could fly I just could not see, but I did not want to give up. A second later my flight mate called knock it off. I unloaded and found myself at 4800′ (floor mort) and we climbed up and returned back to base (RTB). Turns out he had the same issue.’
‘Lessons learned that day. Get in better shape, work on my straining maneuver, don’t let my physical conditioning be the limiting factor in a dogfight and never let it happen again…the next time it does it could spell the end of me, by my own hand of that of an enemy pilot. It never happened again.’
Photo credit: U.S. Air Force