 This module will focus on visual illusions that could cause spatial disorientation. Spatial disorientation is the loss of your orientation in relation to the Earth's surface caused by a lack of visual, vestibular, or proprioceptive sensory inputs to the brain or by misinterpretation of these inputs. Of all of the senses of the human body, vision is your most important sense in obtaining reference information. During flight, it is also the most dominant. Reviewing the module Vision in Aviation to See or Not to See will aid in your understanding of the concepts discussed in this module. Do you realize that even though you may have perfect vision, you may not be seeing the whole picture? Visual perception involves your eyes, brain, and balance mechanism. The balance mechanism and its vestibular and proprioceptive components were discussed in the first module on spatial disorientation. The function of the eyes includes central and peripheral vision. Central vision, also known as foveal vision, involves the identification of objects and the perception of colors. It is a 1-3 degree cone which, during instrument flight conditions, allows you to acquire information from the flight instruments that your brain processes to provide spatial orientation. During visual flight conditions, central vision allows you to acquire external information to judge distance, speed, and depth. Peripheral vision is approximately 82 degrees on either side of the central vision field. Peripheral vision, also known as ambient vision, is involved with perception of motion and attitude cues, and provides peripheral reference cues to maintain spatial orientation. This visual capability enables orientation independent from central vision, which is why we can walk straight while reading. An understanding of how the brain processes sensory information is important so you can recognize and correct spatial disorientation if it occurs. Information from peripheral vision, vestibular signals, and proprioceptors are acquired and processed subconsciously. This process is very rapid. Information from central vision is acquired and processed through a conscious process. This process is much slower. This is a factor in your instrument cross-check for feedback on your status in flight. If you are an experienced and current instrument pilot, you will use your central vision to concentrate on the flight instruments, to override false illusions, and to maintain aircraft control. This skill takes practice, discipline, and concentration. What you have experienced, what you expect to see, and the sensory input you are receiving all influence perception. Which woman do you see here in this picture? There are two, an old one and a young one. Once you focus on one, it is difficult to transition to the other unless certain cues are removed. The flight attitude of an airplane is generally determined by the pilot's visual reference to the natural horizon. When the natural horizon is obscured, attitude can sometimes be maintained by reference to the surface of the earth below. If neither horizon nor surface references exist, the airplane's attitude can only be determined by artificial means such as an attitude indicator or other flight instruments. Earth surface references, or the natural horizon, may at times become obscured by smoke, fog, haze, dust, ice particles, or other phenomena, even if visibility is at or above VFR minimums. Lack of horizon, or earth surface reference, is common on overwater flights, at night, or in low visibility conditions. This lack is especially true at airports located adjacent to large bodies of water or to sparsely populated areas where few, if any, earth surface references are available. There are some geometric shapes that cause you to have visual illusions in your aircraft. These geometric shapes associated with aircraft movement can affect your distance and depth perception. Which lines are the same length? Are the thin lines parallel to each other or crooked? How much longer is line A than line B? Which side of this cube is in the front and which is in the back? It depends on whether you look at A or the B. Many visual illusions can occur and cause you problems during the takeoff and landing phases of flight. You learn to recognize a normal final approach by developing and recalling a mental image of the expected relationship between the length and the width of an average runway surrounding terrain and geometric shapes. Some factors that can create landing illusions are runway width and or length, runway slope, surrounding terrain, fog and haze, smooth solid surfaces, runway lighting. A final approach over flat terrain with an upsloping runway may produce a visual illusion of being high on final approach. If you believe this illusion, you may respond by pitching the aircraft nose down to decrease your glide path, which, if performed too close to the ground, may result in an accident. A final approach over flat terrain with a downsloping runway may produce the visual illusion of being low on final approach. If you believe this illusion, you may respond by pulling the nose up to increase the glide path. This action may result in a low altitude stall or missed approach. With an upsloping terrain with a flat runway, you may have an illusion of being low on final approach. If you believe the illusion, you may respond by pulling the nose up to increase the glide path, which may result in a low altitude stall or a missed approach. A final approach over a downsloping terrain with a flat runway may produce the visual illusion of being high on final approach. If believed, you may respond by pitching the aircraft nose down to decrease the glide path, which, if performed too close to the ground, may result in an accident. Runways with varying widths and lengths are another source of illusions that may affect your perceived glide path. An approach to an unusually narrow or long runway may produce the visual illusion of being high on final approach. If believed, you may respond by pitching the aircraft nose down to decrease your glide path, which, if performed too close to the ground, may result in an accident. An approach to an unusually wide runway may produce the opposite illusion of being low on final approach. If believed, you may respond by pitching the aircraft nose up to increase glide path, which may result in a low altitude stall or a missed approach. Depth perception can also be a problem due to runway width and length. If you have been landing on a narrow runway and then shoot an approach to a wide runway, be aware, your peripheral vision cues may not properly determine the height above the runway during the final part of your approach and flare. The possibility will exist for a hard landing. If your experience is landing on a wide runway and you shoot an approach to a narrow runway, the possibility exists for you to flare too high and have no airspeed. Night flying has illusions also. A final approach during a dark night with no stars or moonlight, with no lights before the runway, and city lights or rising terrain beyond the runway is known as a black hole approach. An approach under these conditions may produce a visual illusion of being too high on the glide path. If you believe this illusion, you may respond by pushing the aircraft nose down to decrease the glide path. This action could cause you to land short of the runway. Autoconetic illusion gives you the impression that a stationary object is moving in front of the airplane's path. This is caused by staring at a fixed single point of light, such as a ground light or a star, in a totally dark and featureless background. The illusion can cause you to have a misperception that such a light is another aircraft on a collision course with you. The false visual reference illusion may cause you to orient your aircraft in relation to a false horizon. This illusion is caused by flying over a banked cloud, night flying over featureless terrain ground lights that are indistinguishable from a dark sky with stars, night flying over a featureless terrain with a clearly defined pattern of ground lights and a dark, starless sky. In addition, problems can be caused during landing by a lack of visual depth and texture caused by blowing dust and snow, fog and haze, over water approaches. Time of day and lighting conditions are the most important terrain features of rolling hills and mountains. You should be aware of the minimum safe altitude for the terrain for your flight path. In this module, you have seen how the eyes can be fooled. How do you defeat spatial disorientation and protect yourself against these illusions? Realize that you are vulnerable to sensory illusions. Obtain an instrument rating and maintain your proficiency as an instrument pilot. Be aware of the times and conditions that could cause you to be subject to visual illusions and spatial disorientation. Do a pre-flight plan to reduce the need for in-flight planning. Study and be familiar with the approach charts for your destination airports. Make it a part of your cockpit management and constantly cross-check your instruments with outside visual references. If you become disoriented, here is a checklist for recovery. Concentrate on flying basic instruments. Get closer to the instruments, remove yourself from the outside environment and its peripheral vision cues and distractions. Increase your instrument cross-check rate. Defer non-essential tasks and maintain aircraft control. If circumstances dictate, communicate your situation to air traffic control. If you are an instrument rated pilot, remember, instrument flying is a skill that erodes with time. Only the frequent use of this skill will allow you to maintain an optimum level of proficiency. Of all of the senses of the human body, vision is your most important and the most dominant sense in obtaining reference information during flight. Visual perception involves your eyes, brain and balance mechanism. The functions of the eye include central and peripheral vision. Peripheral vision will give motion and attitude cues, but poor visual detail. Central vision tells you what the object is, gives you distance and depth perception and lets you see fine details. What you have experienced and what you expect to see influence perception. This is how to protect yourself against these illusions. Realize that you are vulnerable to sensory illusions. Obtain training and maintain your proficiency as an instrument pilot. Study and be familiar with the approach charts for all your destinations. If you become disoriented, concentrate on flying basic instruments. Get closer to the instruments. Remove yourself from the outside environment and its peripheral vision cues and distractions. Increase your instrument cross-check rate. Defer non-essential tasks, remember priorities, control the aircraft. Spatial disorientation is a killer. By being knowledgeable about its insidious effects and by trusting your instruments, you will be contributing to safer skies for everyone.