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attitude. An abrupt downward vertical acceleration, usually in a downdraft, has the opposite effect with the disoriented pilot pulling the aircraft into a nose-up attitude. 

## Visual Illusions 

Visual illusions are especially hazardous because pilots rely on their eyes for correct information. Two illusions that lead to spatial disorientation, false horizon and autokinesis, are concerned with only the visual system. 

## False Horizon 

A sloping cloud formation, an obscured horizon, an aurora borealis, a dark scene spread with ground lights and stars, and certain geometric patterns of ground lights can provide inaccurate visual information, or false horizon, for aligning the aircraft correctly with the actual horizon. The disoriented pilot may place the aircraft in a dangerous attitude. 

## Autokinesis 

In the dark, a stationary light will appear to move about when stared at for many seconds. The disoriented pilot could lose control of the aircraft in attempting to align it with the false movements of this light called autokinesis. 

## Postural Considerations 

The postural system sends signals from the skin, joints, and muscles to the brain that are interpreted in relation to the Earth’s gravitational pull. These signals determine posture. Inputs from each movement update the body’s position to 

the brain on a constant basis. “Seat of the pants” flying is largely dependent upon these signals. Used in conjunction with visual and vestibular clues, these sensations can be fairly reliable. However, because of the forces acting upon the body in certain flight situations, many false sensations can occur due to acceleration forces overpowering gravity. [Figure 3-8]  These situations include uncoordinated turns, climbing turns, and turbulence. 

## Demonstration of Spatial Disorientation 

There are a number of controlled aircraft maneuvers a pilot can perform to experiment with spatial disorientation. While each maneuver normally creates a specific illusion, any false sensation is an effective demonstration of disorientation. Thus, even if there is no sensation during any of these maneuvers, the absence of sensation is still an effective demonstration in that it shows the inability to detect bank or roll. There are several objectives in demonstrating these various maneuvers. 

1. They teach pilots to understand the susceptibility of the human system to spatial disorientation. 

2. They demonstrate that judgments of aircraft attitude based on bodily sensations are frequently false. 

3. They help lessen the occurrence and degree of disorientation through a better understanding of the relationship between aircraft motion, head movements, and resulting disorientation. 

4. They help instill a greater confidence in relying on flight instruments for assessing true aircraft attitude. 

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