A note from the aeromedical division - Brief Article

Approach, Feb, 2002

Lt. Maini has provided us with a terrific story describing spatial disorientation in detail. The physiological event described in the article is actually a vestibular illusion, most likely the somatogyral illusion, not vertigo. Vertigo is a medical condition caused by an abnormality in the vestibular system. This illusion is the result of a misperception of the magnitude and direction of rotation due to stimulation of the sensors in the semicircular canals of the middle ear.

We orient ourselves in space using visual cues, with additional information provided by position sensors in our limbs and skin, as well as inputs from the middle ear. Our peripheral vision supplies the visual cues. When you can't see the horizon these inputs are reduced greatly.

Lt. Maini not only had a total lack of peripheral visual clues, but also experienced a false sense of rotation caused by a normal pedal turn as the aircraft departed the ship. NATOPS calls for the aircraft to climb into a stable hover, then to pedal-turn 45 degrees before climbing from the ship. The aircraft can safely turn up to 30 degrees per second, greatly exceeding the 2-degree-per-second rate required to start fluid movement in the middle ear. Once the turn stops, the fluid may continue to move, causing a spinning sensation. If you add an accelerating climb away from the ship, the otolith in the middle ear is stimulated and may provide additional complex inputs to the brain to further disorient the aviator.

Lt. Maini's experience with spatial disorientation is common and was handled competently. Though spatially disoriented, this naval aviator went back to the basics by recognizing the problem, troubleshooting the event, and using crew coordination to return to the ship.

A note for the flight surgeons and physiologists who read this: Spatial disorientation is a normal physiological event that is a significant aviation hazard. Remember to annually brief all our aviators on the subject. This story could be a good teaching tool on how to handle the events.

Cdr. Rick Erickson, MSC
Naval Safety Center
Aviation Physiologist
Email: rerickson@safetycenter.navy.mil
Cdr. Nicholas L. Webster, MD, MPH
Naval Safety Center
Staff Flight Surgeon
Email: nwebster@safetycenter.navy.mil