We woke up to dense fog Tuesday morning, which made the National Transportation Safety Board hearing concerning the helicopter crash that killed Kobe Bryant and eight others even more relevant. The helicopter pilot entered an area of dense clouds and experienced spatial disorientation due to weather, according to investigators.
Spatial disorientation is an aviator’s inability to determine angle, altitude or speed. The NTSB defines it in more detail:
“Sight, supported by other senses, allows a pilot to maintain orientation while flying. However, when visibility is restricted (i.e., no visual reference to the horizon or surface detected) the body’s supporting senses can conflict with what is seen. When this spatial disorientation occurs, sensory conflicts and optical illusions often make it difficult for a pilot to tell which way is up.
“Contributing to these phenomena are the various types of sensory stimuli: visual, vestibular (organs of equilibrium located in the inner ear), and proprioceptive (receptors located in the skin, muscles, tendons and joints). Changes in linear acceleration, angular acceleration, and gravity are detected by the vestibular system and the proprioceptive receptors, and then compared in the brain with visual information.
“In a flight environment, these stimuli can vary in magnitude, direction, and frequency, resulting in a “sensory mismatch” that can produce illusions and lead to spatial disorientation.”
Other times you may experience similar phenomena include when underwater. Scuba divers are trained to watch which way bubbles travel in the water to determine which direction is “up” or toward the surface.
Seasickness is also caused by the disparity between what your eyes see and the brain perceives and what the fluid between your ears senses (the rolling motion of the seas). Some seasickness can be abated by watching the horizon, allowing your eyes and brain to match the motion that the fluid between your ears is sensing.
NTSB accident data suggests that spatial disorientation may be a precursor to many general aviation accidents, particularly in night or limited visibility weather conditions. Instrument and VFR pilots are subject to spatial disorientation and optical illusions that may cause loss of aircraft control.
In the NTSB hearing Tuesday, Dr. Dujuan Sevillian said the pilot was unable to perceive his altitude and acceleration and underwent a somatogravic illusion, causing the pilot to sense the aircraft was climbing when it was, in fact, not. A somoatogravic illusion is when a pilot incorrectly perceives acceleration as a rise in pitch attitude.
It’s unsettling to think about, but the NTSB says all pilots at sometime or another will experience spatial disorientation. The NTSB set forth guidelines to help pilots through these times:
- If you experience a visual illusion during flight (most pilots do at one time or another), have confidence in your instruments and ignore all conflicting signals your body gives you. Accidents usually happen as a result of a pilot’s indecision to rely on the instruments.
- If you are one of two pilots in an aircraft and you begin to experience a visual illusion, transfer control of the aircraft to the other pilot, since pilots seldom experience visual illusions at the same time.
- If you fly single-engine IFR frequently, consider the investment of an alternate vacuum system or electric standby attitude indicator.