Why does a pilot tend to black out when pulling of steep dive?

A pilot tends to black out when pulling out of a steep dive due to the sudden onset of high gravitational forces, particularly during high-G maneuvers. When a pilot pulls out of a steep dive, the aircraft rapidly decelerates, causing the pilot's body to experience a significant increase in gravitational force. This sudden increase in G-force, known as a positive G, pushes blood away from the pilot's brain, leading to a temporary loss of consciousness or blackout.

The human body can withstand a limited amount of G-force depending on several factors, including the duration and direction of the force, an individual's physical condition, and training. When the G-force exceeds the body's tolerance, it can cause various physiological effects, including:

1. Reduced Blood Flow to the Brain: High G-forces can divert blood flow from the brain toward the lower extremities, depriving the brain of oxygen and glucose necessary for proper function. This can result in a temporary loss of consciousness or blackout.

2. Impaired Vision: Excess G-forces can affect vision, causing a phenomenon known as "greyout" or "redout." Greyout occurs when the G-force restricts blood flow to the eyes, leading to a loss of peripheral vision. Redout, on the other hand, occurs when blood vessels in the eyes become engorged, causing a reddish tint in the pilot's vision. Both greyout and redout can impair a pilot's ability to see and make quick decisions.

3. G-LOC (G-Force Induced Loss of Consciousness): Prolonged exposure to high G-forces can lead to a complete loss of consciousness or G-LOC. This occurs when the brain is deprived of oxygen for a longer period, resulting in a blackout that can last for several seconds. G-LOC poses significant risks to pilots, as it can render them incapable of controlling the aircraft.

To prevent blackouts and other physiological effects of high G-forces, pilots undergo specialized training and use various techniques, such as the Anti-G Straining Maneuver (AGSM). The AGSM involves tensing certain muscle groups, particularly the leg and abdominal muscles, to counteract the effects of G-forces and maintain adequate blood flow to the brain. Pilots also wear G-suits, which are full-body garments that help distribute G-forces more evenly across the body, reducing the risk of blackouts.