 The aerobatic pilot is able to perform flawlessly, even when he knows nothing of the physiological limitations of his inner ear, so long as he has visual reference to the earth while he scans from side to side. It's only when he loses his visual reference that he becomes subject to the false and dangerous sensations of spatial disorientation. Just as dangerous and equally as confusing can be any one of the many seemingly harmless visual illusions that may confuse and threaten a pilot's life. You'll discover both the problems and some solutions in this film. The two main causes of pilot disorientation are either vestibular, referring to the inner ear, or visual in nature. We begin with some visual illusions, which can affect every pilot. Whether he has his instrument ticket or not. So great is our faith in the visual signals we receive that we maintain seeing is believing. The more fitting statement might be, what we see is what we think we see. For example, here's something you must do whenever you come in for a landing. Judge the runway length. Looking at the two lines, AY and AX, how much longer is AX? Before answering, let's remove the surrounding terrain. They're actually identical. The only problem in the air is that you can't eliminate the background, and it influences your judgment of what you see. These visual illusions can be observed in many ways. Do the lines A and B look parallel? They are. Your eye bends them. And the fact that your brain is conditioned to think in terms of perspective can play tricks with your ability to discriminate height differences. This one, of course, is a classic. Which post is the tallest? By now, you have the pattern. They are all the same height. How about this one? It introduces another factor, light, or more correctly, shadow. The three large mounds, when turned over, mysteriously appear to have been dense all the time. Actually, all of these aspects of vision, perspective, depth, perception, shadows, are critical to the task of flying. They're the visual cues your mind needs and uses to make a successful landing. When landing in the high country, for instance, what looks and feels like a normal glide path, especially at night, may be entirely inadequate. If the runway has either an upslope or a downslope. A normal approach to a level runway is about a three and a half or four degree angle, right? No particular problem. However, if you were to use your normal perspective to set up an approach to an upslope runway, you'd be dragging the trees and perhaps not make the runway at all. And if you set up your normal approach to a downslope runway, your glide angle would be excessively steep. And you might very well overshoot because of excessive airspeed. How about the problems of visual cues at night? Here's a simulated runway with lights of different intensities as we turn on final. Most pilots would feel that the aircraft would be level about now. Actually, it's quite a few degrees off, enough to give trouble, particularly in a crosswind. How about the stars at night? Every pilot has mistakenly lined up on one sometime or another. Or the slanting cloud formation. That's had you flying in a banked attitude or climbing toward a fictitious horizon. A thoughtful glance at the turn in bank would have told this pilot he was flying with one wing low. And to keep going in a straight line, he was holding opposite rudder. The slip indicated here tells the story. The list of visual illusions is seemingly endless, but the solution is quite simple. Be alert to situations that are potentially disorienting. And then when they seem to contradict your visual sense, do what the gauges say. Trouble really begins when there are no visual references. When we're on the ground, the combined input from several senses tells us which way is up. Sight gives us a frame of reference. We can see where we are in relation to fixed objects. Feeling gravity's pull on our muscles and joints tells us which way is down. And special parts of our inner ear help give us our sense of balance and orientation. In the absence of visual cues, accelerations can be confusing. Their tugs misinterpret it as gravitational pulls. The result is often disorientation or pilot's vertigo. That's why, without adequate instruments and the ability to use them, a pilot should avoid situations where visual references are obscured. No smart pilot would take off in instrument conditions without an IFR rating and the right equipment. But it's the brief and hazardous exposures to IFR conditions that you think you have enough experience to handle that can lead to tragedy. Next to failing to obtain or maintain flying speed, the greatest number of general aviation fatalities are the VFR pilots who continue flight into bad weather. So your best protection is to avoid those perilous weather conditions. And if you do get caught briefly, have the discipline to believe your instruments, not your impulses. We know that when you're getting signals on three different sensory channels resulting in a message contrary to what your instruments say, it takes a lot of discipline not to react instinctively. This simple demonstration will change the mind of any skeptic who believes he's immune to the effects of vertigo. You indicate with the stick the direction that the body sensations tell you that you're turning. To avoid motion sickness and to cut out outside lights and visual reference points, we will blindfold you and you'll be looking at some blue lights. I'll spin you to the right, but at all times, indicate the direction that the body sensations tell you that you're turning. And you can experience most of the sensations of vestibular disorientation right on the ground. The best way is to attend a local accident prevention clinic. Notice he indicates that he's slowing down. Stopped. Now he indicates that he's turning to the left. Now at this point, I will accelerate you to the left. And you're really turning to the left now, aren't you, sir? Would you remove your hood? Unbelievable? Yes, it is. Yes, it is unbelievable. But by looking at the remarkable mechanics of the inner ear, we can learn how it was able to confuse our subject. We'll be looking at only one set of semicircular canals, although there is a set located on either side of the head, just inside the ear, at about eye level. The three canals, each in a different axis, correspond to the roll, pitch, and yaw planes of any good gyro. Let's look at the movement of just one axis as an example. A cutaway of the canal, which would sense angular accelerations and yaw. Shape something like the shell of a snail. The canal is filled with the fluid. Microscopic hairs embedded in the cupola sense the movement of the fluid. Let's see what happens in our subject's inner ear when he's rotated. Due to inertia, the fluid in the canal lags behind the rotation, thus bending the cupola. And the vestibular nerve transmits a clockwise indication to the brain. As the rotation approaches a constant speed of about 15 RPM, the fluid slowly begins to catch up, all the while giving the impression the subject is slowing down, a false sensation. Had he been kept at a constant 15 RPM for several moments, the cupola would have returned to the vertical position when both fluid and canal rotate at the same speed, giving another false sensation, that of no motion at all. Deceleration causes the subject to sense a counterclockwise turn due to the cupola's tilt in the opposite direction. And when he stopped suddenly to zero RPM, the fluid continues to rush onward, bending the cupola all the way over, indicating a violent turn to the left. What you've just seen isn't just laboratory theory, and it doesn't just apply to inexperienced pilots. Here's Al Hall on the right, an airline captain with more than $30,000. He's in charge of training his company's 747 pilots. Obviously, if there's anyone who should be able to outguess the seat of his pants, it should be Al. Let's watch and see if our theory is correct. It senses how your ear will fool you when you can't see outside the airplane and you don't have any instruments to look at. I'd like to have you put this scarf over your eyes and make sure that you can't see changes of light from the sun. I want you to get your hands and feet off the controls now. And I'm going to put the airplane in a turn, and you'll feel it going into the turn. And then I want you to tell me what you feel. I've now established that it's an angle of bank and a left turn, and it appears constant. It's the left turn. Oh, feels the left turn. Feels like we rolled out of the left turn, man. Real smoothly, though. Feels like we rolled out. I think we're in a right turn now. I think we're just as smooth as we just rolled smoothly around to the right. Unbelievable. Did we roll from left to right, as I was saying? All we did was I just rolled the airplane out to level flight, and we did level flight all the time. And when you rolled your head back, like you reached for an overhead switch, came forward, you felt it like the airplane had gone into a turn to the right and dive into a still level. What do you think of that? It's unbelievable. Yes, it is unbelievable. And if you wish to arrive at your destination safely, remember the inaccuracies of your inner ear. Remember the false sensations you can encounter when you lose visual reference outside your aircraft due to rain, fog, or other phenomenon. And don't forget the pitfalls of visual illusions and how your eyes can deceive you as easily as your inner ear. Briefly put, learn to live with your instruments. It makes good sense.