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 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.  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.  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. 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. 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. Visual Illusions False Horizon Autokinesis Postural Considerations Demonstration of Spatial Disorientation 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. Skid, slip, and uncoordinated turns feel alike.  Pilots feel they are being forced sideways in their seat. Level Coordinated turn  Pull out  Level skid  Forward slip  Uncoordinated turn  Figure 3-8. Sensations from centrifugal force. 3-7