A brownout, or grey-out, may also be experienced by aircraft pilots pulling high positive G forces as when pulling up into a loop or a tight turn forcing blood to the lower extremities of the body and lowering blood pressure in the brain. This is the reverse of a redout, or a reddening of the vision, which is the result of negative G forces caused by performing an outside loop, that is by pushing the nose of the aircraft down. Redouts are potentially dangerous and can cause retinal damage and hemorrhagic stroke. Pilots of high performance aircraft can increase their resistance to brownout by using a G-suit, which controls the pooling of blood in the lower limbs but there is no suit yet capable of controlling a redout. In both cases symptoms may be remedied immediately by easing pressure on the joystick. Continued, or heavy G force will rapidly progress to g-LOC (G force induced Loss of Consciousness).
g-induced Loss Of Consciousness is a condition where a person loses consciousness because g-forces move the blood away from the brain (black out) or move excess blood towards the brain (red out). The condition is most often linked to astronauts and pilots of fighter planes.
Incidents of acceleration-induced loss of consciousness were reported to have caused some deadly aircraft accidents in the 1970s. In the 1980s, in an attempt to reduce the risk of g-LOC related incidents, air force training facilities in many countries began to see centrifugation as a regular part of pilot training.
Aerobatic and fighter pilots may sometimes experience a brownout or grey out between 6 to 8g. This is not a total LOC but is characterised by temporary loss of coloured vision and/or tunnel vision, or even complete loss of vision temporarily, while consciousness remains. They may also be unable to interpret verbal commands. It is possible for vision to go totally black while remaining fully conscious. This condition is termed "blackout". Loss of blood flow to the eyes occurs prior to loss of blood flow to the brain because the pressure within the eye (interocular pressure) counters the blood pressure.
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