Aeromedical Factors

Inversion Illusion Autokinesis An abrupt change from climb to straight-and-level flight can When flying in the dark, a stationary light may appear to stimulate the otolith organs enough to create the illusion of move if it is stared at for a prolonged period of time. As tumbling backwards, known as “inversion illusion.” The a result, a pilot may attempt to align the aircraft with the disoriented pilot may push the aircraft abruptly into a nose- perceived moving light potentially causing him/her to lose low attitude, which may intensify this illusion. control of the aircraft. This illusion is known as “autokinesis.” Elevator Illusion Postural Considerations The postural system sends signals from the skin, joints, and An abrupt upward vertical acceleration, as can occur in an muscles to the brain that are interpreted in relation to the updraft, can stimulate the otolith organs to create the illusion Earth’s gravitational pull. These signals determine posture. of being in a climb. This is known as “elevator illusion.” Inputs from each movement update the body’s position to The disoriented pilot may push the aircraft into a nose-low the brain on a constant basis. “Seat of the pants” flying is attitude. An abrupt downward vertical acceleration, usually largely dependent upon these signals. Used in conjunction in a downdraft, has the opposite effect with the disoriented with visual and vestibular clues, these sensations can be pilot pulling the aircraft into a nose-up attitude. fairly reliable. However, because of the forces acting upon the body in certain flight situations, many false sensations Visual Illusions can occur due to acceleration forces overpowering gravity. Visual illusions are especially hazardous because pilots rely [Figure 17-6] These situations include uncoordinated turns, on their eyes for correct information. Two illusions that lead climbing turns, and turbulence. to spatial disorientation, false horizon and autokinesis, affect the visual system only. Demonstration of Spatial Disorientation There are a number of controlled aircraft maneuvers a pilot False Horizon can perform to experiment with spatial disorientation. While A sloping cloud formation, an obscured horizon, an aurora each maneuver normally creates a specific illusion, any false borealis, a dark scene spread with ground lights and stars, sensation is an effective demonstration of disorientation. and certain geometric patterns of ground lights can provide Thus, even if there is no sensation during any of these inaccurate visual information, or “false horizon,” when maneuvers, the absence of sensation is still an effective attempting to align the aircraft with the actual horizon. demonstration because it illustrates the inability to detect The disoriented pilots as a result may place the aircraft in a bank or roll. dangerous attitude. Level Coordinated turn Pull out Level skid Forward slip Uncoordinated turn Skid, slip, and uncoordinated turns feel similar. Pilots feel they are being forced sideways in their seat. Figure 17-6. Sensations from centrifugal force. 17-8