Contents

About Illusions
What ever the illusion, it will take a few moments for you to get reoriented. If the illusion occurs in trimmed flight the problem is not as severe as it might be if it occurs during maneuvers as it usually does. Spatial disorientation caused by loss of horizon, change in power, banking, or other acceleration forces can lead the pilot to believe that the aircraft is doing something that it is not. These forces cause the pilot’s vestibular and proprioceptive system to give the somatogravic illusion. A pilots first reaction will be to over-control in a direction exactly opposite to what should be done. The only safe procedure during the onset of any illusion is to increase your instrument scan rate.

We have three orientation systems. 75% of our orientation is due to our vision. The autokinetic illusion occurs when a single light is stared at to the point to which it appears to acquire movement. This can be avoided by a frequent shifting of the eye. A sloping cloud deck that extends to both sides of your horizon will appear level. Sloping terrain can give the same illusion. A few lights on a dark mountain can be confused with stars to give a false horizon

The inner ear is a six-axis gyro system and is most protected part of the body. Illusions occur when there is a conflict between the visual input and your inner ear balance. The inner ear reacts to acceleration. A constant acceleration will cause the inner ear to lose its sensing ability. Once a velocity is attained the inner ear cannot take a reading. We must rely on vision and our instruments to ignore the treacherous readings and non-readings of the inner ear. A coordinated turn, a gradual climb or descent provides no tilting sense to the inner ear. A roll of two degrees per second may not be sensed by the inner ear.

The motion (vestibular) system is based on the semicircular canals of the inner ear. The canals detect motions that are rotary, acceleration, and deceleration. As long as fluids lag the motion the motion is detected. A less than 2-degrees per second motion cannot be detected. the most common vestibular illusion is the ‘leans’. A pilot who discovers a vestibular illusion will most likely react quickly in the opposite direction. The canals sense the quick motion and will tend to compel you to go back to the original direction. The entry and failure to recover from both the graveyard spiral and spin are vestibular illusions.

The otolith organ detects gravity and is responsible for illusions of motion that simulate gravity. Acceleration causes to somatogravic illusion. The otolith organ makes you think that that an excessive climb has occurred, the reaction is to lower the nose dangerously. Catapult launches cause this illusion. The inversion illusion is caused when a climbing aircraft levels off. The pilot believes that he is falling over backwards. The missed approach exposes a pilot to ortholithic illusions that may cause a pilot to fail to enter a climb due to believing that level or a descent is a climb. This is due to the acceleration of the aircraft. The illusion is made even worse as it continues.

Our senses fail when we lack visual references. An IFR pilot must have the ability to recognize and ignore the false sensations as they occur. A big part of ability to overcome and ignore lies in knowing when illusions can occur. Knowledge and understanding of what can happen is essential to IFR survival.

The proprioceptive system
A pilot is well advised to fly a normal rectangular pattern at the standard pattern altitude at night and during periods of poor visibility. Spatial disorientation caused by illusions are at the top of fatal accident causes. Runway lights that are brighter than normal give an illusion that they are closer than they actually are. At night use VASI or a glide slope when possible to avoid illusions that may fly you into terrain. A narrower runway than you are normally used to will give an illusion that will cause you to fly a lower final than is normal or safe. An upslope runway can cause an illusion that you are high and will cause you to fly a lower final than is normal or safe. Rain on the windshield will cause an illusion that you are high and will cause you to fly a lower final than is normal or safe. an approach over water or a dark featureless area on final will give an illusion of greater height and will cause you to fly a lower final than is normal or safe. Haze or poor visibility gives an illusion of greater distance which may cause you to maintain excess altitude.

Night Lights
Runway and approach light illusions will always be a problem if you are in an unfamiliar area. For this reason it is always desirable to make a daylight familiarization flight to an airport before a first time night arrival. If there is no VASI or VAPI for vertical guidance if you get too low the runway lights will begin to disappear. A steep approach is always better at night. If there is a strong crosswind and you are crabbing to the runway instead of slipping you will get the illusion of being inverted. If the airport is well lighted in a surrounding dark area you will have an illusion of being higher than you actually are. Again a steep approach has much advantage. Rain on the windshield will give the illusion of being higher than you are. An arrival at an airport with and approach lighting system (ALS) tends to be lower and at a shallower angle than otherwise. If you are low and pitch the nose up as a correction or through the use of flaps, the illusion will indicate that you are rising. Any reduction of power will cause you to land short.

At night, banking into or away from a line of lights will give the illusion that a dive or a climb is occurring. The same dive or climb illusion can happen by a change in aircraft pitch occurs while flying toward a light. Lights that appear dim, as seen through haze, will be reported as more distant than they are. Example: I once reported an airport as in sight from twelve miles when the tower had me on radar at only five miles.

Airport Illusions
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.

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 narrower runway causes an illusion of height; you will fly a lower approach with a tendency to land short.

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 you usually fly into narrow runways, a wide runway will give you a too low illusion. A runway that is more narrow than you are used to will make you seem high. Using the altimeter along with a standard pattern and approach procedure resolves both problems. 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.

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.

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.

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.

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.

Pilots unconsciously make extensive use of their 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.

Night has its own illusions that are covered in the night flight lessons. The distance of lights is greatly affected by the relative clearness and haze existing. A region of no lights such as might exist off the end of a runway toward the ocean can cause disorientation because of IFR illusions. The best solution is to go on instruments until established inland at altitude.

All flying skills, but most importantly instrument flying requires continual practice. The untrained pilot who loses visual reference is like going blind. Stress rises and orientation ceases to exist inside of 20 seconds. You are reluctant to trust your instruments but failing to do so means a loss of flight control. Every pilot must, for himself, determine with respect to all the IFR factors of a flight, the level of acceptable risk. Common sense and caution should reign.

--Where there are no ground features as with water, snow or darkness the illusion is that the aircraft is at a higher altitude than it really is.
--Approaching a downhill runway the illusion is that you are lower than you really are so you will come in higher.

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