直升機(jī)教員手冊 Helicopter Instructor’s Handbook
時間：2014-11-10 08:35來源：FAA 作者：直升機(jī)翻譯 點(diǎn)擊：次
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To view this page ensure that Adobe Flash Player version 9.0.124 or greater is installed. Viewing an object using central vision during daylight poses no limitation. If this same technique is used at night, however, the object may not be seen because of the night blind spot that exists during low illumination. Explain to the student that in order to compensate for this limitation, he or she can use off-center vision. This technique requires that an object be viewed by looking 10° above, below, or to either side of the object. In this manner, the peripheral vision can maintain contact with an object. Ensure that the student understands that, with off-center vision, the images of an object viewed longer than 2 to 3 seconds disappear. This occurs because the rods reach a photochemical equilibrium that prevents any further response until the scene changes. This produces a potentially unsafe operating condition. To overcome this night vision limitation, the student must be aware of thephenomenon and avoidviewing an object for longer than 2 or 3 seconds. The peripheral field of vision continues to pick up the object when the eyes are shifted from one off-center point to another. [Figure 14-5] Visual Illusions Decreasing visual information increases the probability of spatial disorientation. Ensure the student understands that reduced visual references also create several illusions that can induce spatial disorientation. Many types of visual illusions can occur in flight and it is important that the student becomes familiar with the various types to include: . Flicker vertigo—much time and research have been devoted to the study of flicker vertigo. A light flickering at a rate between 4 and 20 cycles per second can produce unpleasant and dangerous reactions. Such conditions as nausea, vomiting, and vertigo may occur. On rare occasions, convulsions and unconsciousness may also occur. Flicker vertigo is why the regulations allow pilots to disable the strobe lights and anti-collision beacons while flying in the clouds. . Fixation—occurs when pilots ignore orientation cues and fix their attention on a goal or an object. This is dangerous because helicopter ground-closure rates are difficult to determine at night. . False horizons—cloud formations may be confused with the horizon or the ground. While hovering over terrain that is not perfectly level, the pilot might mistake the sloped ground in front of the helicopter for the horizon and cause the helicopter to drift while trying to maintain a stationary position. Another example is a lighted road climbing a mountain side can easily be mistaken for a flat horizon. . Confusion with ground lights—a common occurrence is to confuse ground lights with stars. When this happens, the pilot unknowingly positions the helicopter in unusual attitudes to keep the ground lights—believed to be stars—above them. [Figure 14-6] . Relative motion—the illusion of relative motion can be illustrated by an example. A pilot hovers a helicopter and waits for hover taxi instructions. Another aircraft hovers alongside. As the other aircraft is picked up in the first pilot’s peripheral vision, the pilot senses movement in the opposite direction. . Altered planes of reference—when approaching a line of mountains or clouds, the pilot may feel the need to climb despite adequate altitude. Also, when flying parallel to a line of clouds, pilots may feel that they need to climb even though their altitude is adequate. . Structural illusions—these illusions are caused by heat waves, rain, snow, sleet, or other factors that obscure vision. For example, a straight line may appear to be curved when seen through a desert heat wave or a wingtip light may appear to double or move when viewed during a rain shower. . Height and depth perception illusion—due to lack of visual references when flying over desert, snow, water, or other areas of poor contrast, the pilot may experience the illusion of being higher above the terrain than is actually the case. This illusion may be overcome by dropping an object, such as a chemical light stick or flare, on the ground before landing. Another technique used to overcome this illusion is to monitor shadows cast by nearby objects, such as the skid shadows at a hover. Flight in an area where visibility is restricted by haze, smoke, or fog produces the same illusion. . Size-distance illusion—results from viewing a source of light that is increasing or decreasing in luminance (brightness). The pilot may interpret the light as approaching or retreating. . Autokinesis—when the pilot stares at a static light in the dark, the light appears to move. This phenomenon can be readily demonstrated by staring at a lighted cigarette in a dark room. Apparent movement begins in about 8 to 10 seconds. Although the cause of autokinesis is not known, it appears to be related to the loss of surrounding references that normally serve to stabilize visual perceptions. This illusion can be eliminated or reduced by visual scanning, by increasing the number of lights, or by varying the light intensity. The most important of the three solutions is visual scanning. You should not stare at a light or lights for more than 10 seconds. This illusion is not limited to light in darkness. It can occur whenever you stare at a small, bright, still object against a dull, dark or nondescript background. Similarly, it can occur when a small, dark, still object is viewed against a light, structureless environment. Anytime visual references are not available, pilots are subject to this illusion. Instructors can also relate this illusion to the helicopter’s landing light. It becomes very easy to focus on that one beam of light and not see the peripheral vision cues of lateral or rotating movement. Staring into the landing light also tends to ruin much of the accumulated night vision, leaving the pilot nearly blind when the landing light is extinguished . Reversible perspective illusion—at night, an aircraft may appear to be moving away when it is, in fact, moving toward a second aircraft. This illusion often occurs when an aircraft is flying parallel to another’s course. To determine the direction of flight, aircrews should observe aircraft lights and their relative position to the horizon. If the intensity of the lights increases, the aircraft is approaching. If the lights dim, the aircraft is moving away. Also, remembering the “3 Rs” helps identify the direction of travel when other aircraft are encountered. If the red aircraft position lights are on the right, the aircraft is returning (coming toward the observer). [Figure 14-7] |
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