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Illusions
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Contents
…About Illusions; …The Proprioceptive System; …Night Lights; …Airport Illusions; …IFR Precepts; …You and Illusions; …Black Hole Landing; …Narrow Runway; …Wide Runway; …Down Slope Runway; …Variable Visibility Approach; …Rain; …Creating Graveyard Spiral; …Creating Autokinesis Illusion; …Creating Elevator Illusion; …Creating Coriolis Illusion; …Creating a False Horizon; …Creating Inversion Illusion; …Creating the Leans; ...Lighting Illusions; ...Rain Effect; …Vertigo; … Spatial Disorientation; …Why?; …

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.

IFR Precepts
--You cannot fly IFR without instruments.
--The inner ear is accurate only when supported by visual reference.
--Disorientation may take less than 20 seconds.
--IFR risk cannot be eliminated but it can be reduced.

You and Illusions
1) Illusions can and do occur to everyone
2) Proper planning for strange airport conditions is essential
3) Weather and poor visual conditions make strange airport conditions worse.
4) Rely on your instruments to help your sense perceptions
5) Maintain situational awareness, know where you are.
6) Use airport systems and lights for directional and slope help.
7) Your physical condition can make matters better or worse.

Example:
There are some optical illusions that relate to nearby aircraft. An aircraft below you will appear to be above you. While getting closer it will appear to descend through your horizon. All the time it is straight an level below you. Avoid the temptation to dive.

Black Hole Landing
When it is very dark you are subject to illusions. Your seat position may make you more or less subject to these. Aircraft seats are situated by a "Design Eye reference Point" (DERP) that is supposed to give a view over the cowl and at the instrument panel. It is not marked on the aircraft but is part of the aircraft design.

If your seat is too low during dark conditions, you will only be able to see runway lights if you are in a descent. The pilot tends to set up a constant angle for their field of view on approach. During daylight, you use the "point on the windshield" to maintain this angle. If the aim point drifts upward you are in an excessive descent; if it drifts downward you are too high. It works the same at night but the references are fewer.

The black hole illusion begins out a few miles on final. The field and lights will be foreshortened. Getting closer the runway should rise in the field of view. If the aircraft is descending the foreshortened view will remain constant. The eye/brain interpretation of this is that the constant foreshortened runway is an indication of a constant angle approach. This is the "everything is fine" illusion of the black hole. During the final phases the daytime depth perception does not work very well.

When flying into a black hole or ‘featureless terrain’ you must use a correctly set altimeter to counter the illusion. Fly a full pattern using your altimeter and a standardized procedure for a stabilized approach. This is the best way to assure yourself that you will not meet an obstacle on final. This is a combined IFR/VFR approach and requires that you be capable of controlling the aircraft accurately without visual references. The normal order of viewing runway, lights, and dark areas is so changed illusions of being higher occur. If the illusions are believed, touchdown can occur before reaching the runway.

The "black hole illusion" has a dramatic effect on straight in approaches to a runway. The stabilized constant angle approach will appear to exist as an illusion while you fly an arc that flies you into the ground. Do not fly a straight in approach to a runway at night. Know the pattern altitude. Fly somewhat farther out on down wind than appears appropriate. Use a standardized configuration approach just as you would in daytime. Fly the VASI or VAPI if available. Failure to follow the above recommendations may cause you to make a premature descent. Over flying featureless terrain without lights on an approach that deprives you of the height clues can fly you into the ground.

Narrow Runway
A narrow runway can create the illusion of a high approach. Narrower and shorter than familiar runway will give illusion that you are higher than you are. Excess speed is most common problem. Fly the numbers and avoid straight-in arrivals. Prepare for go-around, do it earlier than usual.  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.

Wide Runway
The illusion associated with a wide runway causes the risk of flaring rather high above the runway with a hard ground contact to follow.

Down Slope Runway
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 predict 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.

Variable Visibility Approach
If, while on approach, you should suddenly enter an area of reduced visibility you will get an illusion of a sudden pitch up in aircraft attitude. Failing to recognize this illusion will lead to an instinctive and abrupt descent in the approach flight path.

Your ability to determine distance is greatly affected by haze. It is not unusual to call a distance at over twice the actual distance. The sudden appearance of bright lights during an a night approach through haze will create the illusion that the airport is much closer than previously realized. This results in a high approach.

Rain
Rain gives the illusion of being higher than you actually are. Combined with haze you will fly lower approaches during rain.

Creating Graveyard Spiral
Have student close eyes, head forward. Have student try to hold aircraft level. In a few seconds a slight bank should occur with a gradual increase. There will be a gradual descent, an increase in airspeed, and an increase in bank angle. Effort of pilot to correct these will only make them worse.

Creating Autokinesis Illusion
Cover or darken panel. On a night without either moon or stars, fly toward a single light. Have student stare only at that one light. After a while the light will appear to move. Student should try to keep the light in one place. Aircraft control will be lost.

Creating Elevator Illusion
Caused by quick upward acceleration as in updraft. Climbing sensation causes dive reaction. Could be caused by downdraft which results in climb reaction on controls.
Simulation:
Eyes closed. Make 90-degree turn with very slow bank entry from level into a 50-degree bank attitude. Student should have illusion of a climb. This same illusion can occur when caught in updraft. A sudden downdraft can give illusion of dive even though aircraft remains in level attitude.

Creating Corollas Illusion
Caused by abrupt head movement during a constant rate turn that has existed long enough to stabilize the inner ear. Gives sensation of motion on another axis. Attempts to correct
Simulation:
Eyes closed, head down and tilted (Cover AI). Enter extended constant rate turn until student no longer senses turn and bank. Have student make sudden head movement to instruments and open eyes. Student should sense rotation on another axis. May react to dangerous flight attitude.

Creating a False Horizon
Results from cloud formation that slopes. Problem can be made worse by angled road lights or light patterns. Pilot thinks horizon is out of level and attempts to align with illusion. Dangerous attitude results.
Simulation:
Eyes Closed or under hood. On a dark and hazy night fly diagonally across a freeway where other lights are infrequent. Light pattern could pilot to react with dangerous flight attitude. In IFR conditions this will occur as you break out of a solid ceiling.

Creating Inversion Illusion
Caused by abrupt change from climb to level flight. The pilot senses that he is falling backwards. The instinctive response of lowering the nose only makes the sensation worse.
Simulation:
Eyes closed. Have pilot enter and trim for climb. When senses have had settled, have student push yoke forward to nose low attitude while opening eyes. The pilot should sense feeling of going over backwards.

Creating the Leans
Eyes closed. Enter a bank so slowly that it might not trigger the inner ear motion senses. Once into the bank, make an abrupt correction. The student will react to his mistaken senses then by re-entering the previously created bank and will remain there.

Lighting Illusions
Pilot mistakes roadways for runways. Give illusion of being quite close when lights are bright. High approach results. Low approach results when runway is approached over dark area. Don’t use landing light until close to ground. The visual cues used for a normal night landing seem much the same as you get with a rapid increase in sink rate.

After MDA the lights at the airport get brighter. Illusion is that you will fly right into the lights.
The normal tendency is to fly low when you can't see how high you are.
The more up-slope the runway the lower you must be to appear on the approach slope
The combination of up-slope and lights makes the situation even worse.
A down-slope will tend to make you high and fast. With lights illusions may cancel each other.

 Rain Effect
The curve of the aircraft windshield when impacted by sufficient rain will give a frosted-glass look from the interior. Heavy rains are accompanied by turbulence, downdrafts and wind shear.
All navigation aids except possibly GPS can be affected by heavy rain. Visual illusions that can occur require the pilot to pay close attention to altitude, rates of descent, and aircraft attitude.
Rain greatly increases the noise level in the cockpit and can make all communication difficult.

Illusions from the rain-covered windshield can lead the pilot to believe he is high on an approach. The illusions are of several types such as having a halo around a light, a runway appearing much shorter than usual or erroneous distance decisions since things seem further away. Approach lights appear lower. In general, illusions make you believe you are higher than you actually are, further away than you are actually are, and lights larger but not brighter. If this is a familiar airport your preconceptions are very dangerous when in conflict with these illusions. Reliance on aircraft and navigational instruments are the only safe recourse. Accept the fact that going from instruments to visual reference in rain is the most accident-prone region of IFR flight.

Simulation
Under the hood have pilot turn toward a TV tower while looking at compass. Will cause illusion of climb/descent situation that does not exist.

Vertigo
--90% of vertigo related accidents are fatal.
--Vertigo occurs when what you see, feels wrong.
--The three orientation systems of our body are in conflict as to what has happened and where we are.
--When the three systems are working in conjunction we are comfortable and oriented.
--We are up to 80% dependent upon our eyesight.
--Our vestibular (inner ear) system gives us upright, turning and velocity change feelings.
--Our 'butt feeling' is called kinesthetic and gives a sense of gravity.
--Vertigo can be of two types, (1) you are unaware of any disorientation, and (2) when you are aware.
--You first must recognize the existence of confusion typical of vertigo.
--Once vertigo is recognized, the cure is to force yourself to believe your instruments.
--Believe your instruments but verify that all are operating properly.

Spatial Disorientation
--90 percent fatalities when accident occurs
--VFR into IFR most common cause
--Then comes flight in marginal VFR
--Number three is loss of vacuum pump
--Last major cause is vertigo

Why?
--Eyes will believe what your eyes are preconditioned to see
--A slow vacuum pump failure takes about two minutes to be noticed and results in 80 percent fatality rate.
--Declare an emergency
--Request direct to nearest VFR or do it on your own.

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