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What may lead to “red-out”?

  • A

    Excessive positive “g” manoeuvres

  • B

    Excessive negative “g” manoeuvres

  • C

    Sudden decompression at high altitude

  • D

    Prolonged exposure to carbon monoxide

NEGATIVE “G” ACCELERATIONS

During negative “g” accelerations, blood is forced into the head rather than the feet (positive “g” accelerations). Blood is forced into the brain, eyes, and upper body. This increases pressure in the blood vessels of the head. The symptoms experienced during negative “g” forces are discomfort, headache, difficulty in breathing, slowing of the heart, red out of the eyes as the lower eyelid is pushed up and the blood vessels in the face and eyes may eventually burst. The human body is much less tolerant of negative “g” forces than positive “g” forces. It is tolerant only up to -3G. An example of negative “g” activity is inverted flight.

  • Red-out is a visual effect that occurs when negative G forces cause blood to be forced into the eyes, increasing pressure in the retinal vessels. This results in the pilot’s vision taking on a reddish tint (same colour as the blood) and may be accompanied by blurred vision and a sensation of pressure in the eyes.

Positive g-forces → grey out and eventually black out
Negative g-forces → red out

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