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Landing Illusions 2010-03-18
You and every other pilot is susceptible to illusions. When any of our three flight senses (visual, auditory and kinesthetic) give erroneous information our mind produces inaccurate information. Flying illusions are most likely to occur at airports due to visual information. Illusions do not cause accidents. Rather, it is a pilots reaction to the illusion that precipitates an accident. The best way to overcome the negative effects of airport illusions is with experience. Even the most experienced pilot can be fooled. Our three flying senses fool us by misinterpreting distances, velocity and relationship. Vision is the number one creator of illusion. Over our life time of living and flying we have learned that if two things are of the same size and one appears larger it is nearer. If we know two lines are parallel then when they appear farther apart that is the near end. As we fly we learn an approach slope for our aircraft at our home airport. Our brain has developed a data bank of how things are supposed to be at airports. The terrain around the airport can also be an illusion creating factor. Use all the electronic and visual (VASI) help you can get. Width You should practice landings at airports of varying width. All too often you become overly familiar with airports of a consistent length and width. This familiarity interferes with your perception of an airport of different dimension. A narrow runway can create the illusion of a high approach. The AIM Chapter 8-1-5 states that the pilot who does not recognize this illusion will adjust his perceived approach path to fly lower. Once the pilot realizes that he is low it is vital that full power be applied while maintaining approach speed with yoke pressure. No trim changes. Once the proper glide path has been intercepted the power can again be reduced and the stabilized approach resumed. The illusion associated with a wide runway causes the risk of flaring rather high above the runway with a hard ground contact to follow. Visibility The atmosphere can create illusions. Clear clean air makes everything seem closer. Hazy or smog conditions makes things hard to see and apparently further away. Note: Be aware of this when reporting distances at strange airports. The effect of sunlight in creating shadows is an important part of our visual data bank. At night these shadows are not there. The absence of contrast and background at night is a major cause of night landing and takeoff accidents. Precipitation will distort visibility through the windshield and make to think you are higher than you actually are. Speed Our vision is the major source of our cues related to speed. However, much of our speed information comes from our peripheral vision and is often not consciously entered into the brain. The unfamiliar tangential velocity of the ground passing by in a low level bank may appear so fast as to make us pull back on the yoke without regard to the air speed. Stall-spin. This is the classic sequence of the downwind turn from base to final. We have learned to judge both the proximity and speed of an known object crossing in front of us. Closer things seem to move faster. Expectations We are all subject to illusion because we have come to expect certain appearances to occur. When we are told to look for traffic, we expect to see that traffic. If we don't see the traffic tension rises; if we see any plane we have our expectation satisfied and we stop looking. We shouldn't. The traffic we see does not have to be the same traffic we should be looking for. Slope Gives identical illusion as wide runway but is much more likely to cause the pilot to over-shoot the runway. A runway sloping away will give the illusion that you're low on the approach. A runway that slopes toward you can give the illusion of height. One of the most difficult runways is the one with a mound in the middle. This gives the worst of both illusions. In landings where you project the possibility of illusions, it is vital that you proceed with the landing using a standard procedure to establish a stabilized approach. The making of predictable changes of power, flaps, and trim becomes very important as the landing progresses. 'Winging' it for changes in these approach elements means that you are subjecting yourself to the effects of illusion. A pilot who fails to recognize illusion is going to make changes as though what he sees is reality. Any airport that differs from our experience because of runway dimension shape or slope is going to give us an illusion. If a runway slopes away from us our perception (illusion) will be that we are too low. If the runway slopes toward us we will perceive ourselves as being too high. If we react to the illusion we will find ourselves both high and long from the anticipated touchdown point. A wide runway or one whose lights make it appear wider will give the illusion of a low approach causing the pilot to stay too high. A 3 degree approach to an upslope runway and the illusion is that you are high. The same upslope runway made narrower and you will find yourself low. A down-slope runway creates a "low" illusion which can cause long landings on short runways. I have found the best way to counter airport illusions is to have a constant pattern procedure based on a stabilized airspeed and full flaps. I know that even in the worst conditions of illusion I will be close on final . Visual deception Pilots unconsciously make extensive use of there peripheral vision. Level flight, banks, climbs, and descents rely 80% on peripheral vision. (See downwind turns) At low levels our peripheral vision gives us a sense of speed. Over time we develop a peripheral sense as to what "normal" low level speeds are. Add a tailwind, low altitude, a bank to final approach, and a peripheral sense of a "high" speed. We now have an illusion causing a pilot response that says to pull back on the yoke to reduce the speed. The pull merely makes the bank steeper and initiates a low level stall spin. Recovery not possible. A final approach over high terrain leading to the runway gives an illusion of a low fast approach. An approach over terrain that makes the runway seem like an aircraft carrier will give an illusion of too high and too slow. Comment		External Links  Recent articles Additional Endorsements High performance aircraft over 200 hp BR Complex aircraft Gear and flaps BR Tail wheel ... Yoke Control P The third skill of taxiing is the use of the yoke which needs to be positioned so that a wind gust will not flip the airplane over... 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