An archaic definition of disorientation literally meant "difficulty in facing the east."  To the pilot, it more often means "Which way is up?"  Disorientation, or vertigo, is actually a state of temporary spatial confusion resulting from misleading information sent to the brain by various sensory organs. The body's elaborate navigational system was superbly designed for locomotion on the ground at a normal gait, but in an aircraft, during sudden acceleration or radial flight, it can trick you.

The most difficult adjustment that you must make as you acquire flying skill is a willingness to believe that, under certain conditions, your senses can be wrong. When you are seated on an unstable moving platform at altitude (and your vision is cut off from the earth, horizon, or other fixed reference) and you are exposed to certain angular accelerations or centrifugal forces (which you cannot distinguish from gravity forces), you are susceptible to innumerable confusing, disorienting experiences.

In a level turn, you may think you are in straight flight or climbing. In a coordinated, banked turn you may believe yourself to be in straight and level flight. In recovery from a level turn, you may feel as though you are diving. In a left turn - if you suddenly bend your head forward - you may think you are falling to the left.

These alarming sensations are due primarily to misinterpretation of messages sent to the brain by the two primary sensory organs: (1) the semicircular canals of the inner ear, and (2) groups of pressure-sensitive nerve endings located mainly in the muscles and tendons. These organs tell you where you are in relation to the ground, your normal environment. When your eyes are open and your feet are on the ground, they serve you well. You have little trouble deciding which direction is up or down. In an airplane, though, these organs may send your brain inaccurate reports.

The semicircular canals in each inner ear consist of tiny hollow tubes bent to form a half-circle. Each tube (canal) is positioned approximately at a right angle to the other two canals and each is filled with a fluid. At the outer end of each there is an expended portion containing a mass of fine hairs. Acceleration of the inner ear assembly in any direction sets the fluid in motion within the appropriate canal causing the hairs to deflect. This, in turn, stimulates nerve endings and sends directional messages to the brain. Operating as a unit, this detection system forms a device by which we can readily identify "yaw," "pitch," and "roll."

With this perfect arrangement, it appears that you should never have the least bit of difficulty ascertaining your direction and attitude. However, as in all complex systems, there is a certain amount of built-in error. In aviation, we sometimes refer to this type of a problem as "instrument lag."  If the rate of directional change is quite small - and not confirmed by the eyes - the change will be virtually undetectable and you probably will not sense any motion whatsoever.

In straight and level flight the fluid in the semicircular canals is resting and the little hair detectors alert and ready for action. Any directional change of your airplane will cause a reaction in the proper canal and signal to the brain which direction the aircraft has moved.

As you enter a constant-rate turn (such as a standard rate 3 degree/second turn), the system goes to work; the hairs bend over and the proper signal travels to the brain indicating the direction of turning. Continuing the same turn for about 30 to 45 seconds will allow the fluid in the canal to catch up with the pilot and aircraft and the hairs will be pushed back to their upright position.

Here's where trouble begins!  Inside the airplane, if you are unable to see the ground and establish visual reference you are just seconds away from the famous graveyard spiral. You're in a turn but your inner ear machinery tells you that you're straight and level. Now, as the airspeed builds up in the turn you may think you are in a level dive and pull back on the control column. Increased back pressure on the controls will only tighten the turn and cause structural failure or a curving flight path into the ground. But suppose, by either a glimpse of the horizon or a recall of some "needle-ball-airspeed" technique, you are able to get the airplane squared away again to straight and level flight.

The fluid, which continues to turn while you are returning to level flight, begins to creep back to neutral after you level the airplane. Because of its momentum, the fluid continues to flow after the canal has come to rest - bending the hairs along with it. You really are straight now, but you have the sensation of turning in the OPPOSITE direction from which you have just recovered. You instinctively bank away from the imaginary turn - and the cycle starts all over again.

Without instrument training, the chances of maintaining normal aircraft attitude in limited visibility are extremely rare. Repeated small control movements may eventually create a sensation of gradual turning. You may misinterpret the degree of bank and have a false impression of tilting when in a skid or a slip.

Spatial disorientation occurs most often in instrument conditions created by rain, fog, clouds, smoke or dark nights. It is aggravated by other factors such as lack of recent instrument experience or training, attempts to mix VFR and IFR, unfamiliarity with the aircraft or flight situation, fear or worry, and excessive head movements.

You can overcome the effects of vertigo by relying upon your aircraft's instruments. Read your instruments!  They are the best insurance you will ever have. Remember, though, that the time required to shift from VFR to IFR may be long enough for the aircraft to enter a dangerous attitude.

Bear in mind that vertigo can occur ANYTIME that the outside visual reference is temporarily lost - during map reading, changing a radio channel, searching for an approach plate, fuel managing, computing a navigational problem or whatever else you might need to do inside the cockpit. Nearly all experienced pilots have had a brush with vertigo, usually minor and of short duration. It CAN be disastrous, however, "Pilot error," resulting from vertigo, has been identified beyond any doubt as the direct contributing cause of many accidents.

To become familiar with disorientation symptoms, ask your AME or nearest GADO (General Aviation District Office) specialist to arrange a brief demonstration in a Barany (rotating) chair. This will quickly and safely show you how overwhelming vertigo can be. It would be to your advantage to attend any of the FAA Accident Prevention Programs which are presented frequently throughout the country. You GADO inspector can advise you of the time and location of the next program in your vicinity. Disorientation is also included in the FAA-coordinated Physiological Training Course. Complete information regarding this training may be obtained by contacting any of the addresses listed in the back of this handbook.

   The danger of vertigo may be reduced by:
      1. Understanding the nature and causes of the condition.
      2. Avoiding, if possible, the flight conditions which tend to cause vertigo.
      3. Obtaining instrument flight instruction and maintaining proficiency.
      4. Having faith in the instruments rather than taking a chance on the sensory organs.
      5. Remembering that it can happen to ANYONE!