Postural Considerations  Autokinesis  Inversion Illusion  Elevator Illusion  Visual Illusions  Demonstration of Spatial Disorientation  False Horizon  Figure 17-6.  Sensations from centrifugal force.  17-8  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 because it illustrates the inability to detect  bank or roll.  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,” when  attempting to align the aircraft with the actual horizon.  The disoriented pilots as a result may place the aircraft in a  dangerous 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, affect  the visual system only.  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 17-6]  These situations include uncoordinated turns,  climbing turns, and turbulence.  An abrupt upward vertical acceleration, as can occur in an  updraft, can stimulate the otolith organs to create the illusion  of being in a climb. This is known as “elevator illusion.”  The disoriented pilot may push the aircraft into a nose-low  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.  An abrupt change from climb to straight-and-level flight can  stimulate the otolith organs enough to create the illusion of  tumbling backwards, known as “inversion illusion.” The  disoriented pilot may push the aircraft abruptly into a nose- low attitude, which may intensify this illusion.  When flying in the dark, a stationary light may appear to  move if it is stared at for a prolonged period of time. As  a result, a pilot may attempt to align the aircraft with the  perceived moving light potentially causing him/her to lose  control of the aircraft. This illusion is known as “autokinesis.”  Skid, slip, and uncoordinated turns feel similar.  Pilots feel they are being forced sideways in their seat.  Level  Coordinated turn  Pull out  Level skid  Forward slip  Uncoordinated turn 