The Disorient Express
Despite the best training and technology, why do pilots still die from not knowing which end is up?
- By Tom LeCompte
- Air & Space magazine, September 2008
DEPT OF DEFENSE
(Page 2 of 7)
Research in the 19th and early 20th centuries helped shed light on the vestibular system and how it maintains equilibrium. In 1906, Robert Barany devised a swivel chair to simulate the effects of spatial disorientation on pilots.
At an FAA-sponsored safety seminar in Rhode Island recently, program manager Jack Keenan offered me a seat in a Barany chair, a device not unlike a barber’s chair, with an ersatz control stick. As a group of other pilots stood around, he blindfolded me and began to spin the chair to the left, telling me to move the control stick in the direction of the spin. I dutifully moved the stick to the left.
As Keenan gently turned the chair, he said to the group, “Your body keeps you alive. We learn to recognize cues from our environment.” The problem, he added, “is that our bodies are meant to walk on Earth.” As he spoke, the chair seemed to quit spinning. I moved the stick to the neutral position. Keenan then rattled off a litany of phenomena ready to befall pilots: the leans, the graveyard spiral, the inversion illusion, the elevator illusion, false horizons (see “Vertigo: A Primer,” below). As he spoke, the chair then seemed to reverse direction, spinning to the right. I moved the stick to the right. Some in the group tittered. Keenan then pulled off the blindfold, and I saw that the chair had stopped. “Get up carefully,” warned Keenan, helping me to my feet. “You’re still spinning.” Three other volunteers followed my lead. In each case, Keenan first got the chair spinning. After a bit, he gently brought the chair to a stop. In each case, the volunteer moved the stick exactly as I did.
The inner ear is designed to detect motion, or rather, acceleration. Thus, when the chair began to turn, I sensed it. However, once the turn rate was constant, the fluid in my inner ear returned to equilibrium, and without the benefit of visual cues, I could not tell the difference between turning and sitting still. So when the chair stopped turning, I sensed that as a turn in the opposite direction.
Vestibular illusions fall into two categories: somatogyral, for spinning illusions (“somato” is Greek for “body”), and somatogravic, for acceleration illusions. The Barany chair demonstrates a basic somatogyral illusion. An airplane in a stable, level turn will feel the same as an airplane in straight-and-level flight. If the airplane is returned to straight-and-level flight, or if the bank is decreased, a pilot’s natural reaction would be to make a correction that would steepen the actual turn. If at the same time the pilot’s head were tilted—if he were reading a map or picking up a pencil—the deception to the vestibular system would be compounded along a third axis, meaning that when the airplane returned to straight-and-level flight or the pilot lifted his head, he would sense not only a turn in the opposite direction but a feeling of pitching up or down.
Somatogravic illusions refer to situations in which an airplane that begins accelerating will feel the same as one climbing, and an airplane decelerating will feel the same as one descending. Because we live on the surface of the Earth, where the force of gravity pulling us toward the ground is more or less constant, or 1 G, our vestibular system cannot
distinguish the difference between pitch and acceleration. Today’s full-motion simulators take advantage of this fact to create the illusion of flight. For example, inside the simulator pod, as the pilot moves the throttles forward for takeoff and sees and feels the “airplane” accelerating down the runway, the pod itself begins to tilt up. The motions created by the simulators are so realistic that students have become airsick in them.
In 1917, Elmer Sperry invented the gyroscopic turn indicator, based on a similar device he had invented for ships. The indicator joined Sperry’s gyroscopic compass to make up what would later be the core of the panel for instrument flight. But as late as 1928, the idea of flying solely by reference to instruments—“flying blind”—remained as foreign as travel to other planets. Pilots were convinced that their most valuable tools were skill and instinct.