Principal Air - Flight Training / Charter in Canada

Principal Air - Flight Training / Charter in Canada, Learn to Fly


Unit D 30460 Liberator Ave. (Just past the Main Terminal)
Abbotsford International Airport
V2T 6H5
follow us on:   Facebook Facebook

Landing/Takeoff Considerations, Part III: Illusions

“We read the world wrong and say that it deceives us”

--Rabindranath Tagore--

As that great American philosopher Yogi Berra said, “You can see a lot by just looking.” Unfortunately, if you are not looking in the right place at the right things, you can be sadly tricked into unsafe actions. The world is full of illusions, sights and sounds that fool our senses into thinking things are one way, when they are, in fact, another. As Alice in Wonderland said “Curiouser and Curiouser.” 

Understanding the various illusions to which we are subject during flight is important. It’s particularly important when we are operating an aircraft in close proximity to that unforgiving element, the surface of the planet, which is frequently the case on takeoff and landing.

In human factors terms we speak about the four keys to successful practice: knowledge, awareness, attitude, and discipline. They are listed in that particular order for a good reason. Knowledge is the first and primary key. If you don’t know about something, you have no entry point. The beginning of any process for successfully dealing with an issue is to know what it is, how it works, and what must be done to mitigate its potentially negative effects or maximize its potentially positive effects.

Awareness, the second key, speaks to the process of recognizing, to becoming alert to a phenomenon. First, we must know; second we must become aware.

Attitude, the third key, speaks to the desire to do the correct thing, to take the correct action. We can know and be aware, but, if we do not want to make the correct moves, knowledge and awareness go sadly to waste.

Finally, discipline speaks to the determination to do the correct thing each and every time. Discipline does not seem to come naturally to many of us, myself included. It requires a level of commitment and determination and decision-making that, to many people, seems artificial. However, checking for sediment in our fuel is something we would hopefully choose to do each and every time we fly and not just when the spirit moves us.

There are several illusions that plague us on takeoff and landing.  It is very helpful to know about them, to maintain an awareness of them, to choose to take the necessary corrective actions, and to be committed to taking those actions each and every time we takeoff and land.

Over the past couple of months, we have talked about the effects of slope and wind on the performance of an aircraft on takeoff and landing. Slope, wind, and manoeuvring close to the ground are also able to produce some very interesting and potentially dangerous illusions pilots. If we know what these illusions are, how they function, and what we must do the respond to them in a positive manner, our flying safety will be greatly enhanced.

In and of themselves, illusions are not a problem nor are they dangerous. Responding to them as thought they were the truth is.

So, let’s take a look at some of the common illusions we might experience on takeoff and landing.

Sloping runways can produce some very interesting illusions called shape constancy illusions. We are genetically terrestrial beings evolved over a long period of time to deal with living, working, and protecting ourselves from harm on the surface of the planet. Our visual equipment works best and most efficiently when we are using it to view things in the horizontal plane.

Why does the moon appear so much larger just as it emerges over the horizon than it does when high in the sky? Our visual equipment is designed to magnify and detail items of interest to our survival—those things on our own plane of action. Historically, our delights and our threats come at us in the horizontal plane so our perceptual equipment has evolved to make that information most clearly available to our brains for evaluation and possible action.

Slope distorts our perception. This distortion is the natural result of our experience and our genetic perception. We can, however, learn to deal with information for what it is rather than the illusion it presents.

On approach for landing, an up-sloping runway presents us with the illusion that we are too high; a down-sloping runway presents us with the illusion we are too low.

The easiest way to simulate the illusions resulting from a sloping runway is to hold your arm straight out from your shoulder toward the front, palm down with your hand flat, level with horizontal plane. This is what a level runway looks like on a normal 3-5approach. Now, tilt your hand up 10. This is the view you see when setting up for landing on an up-slope runway. The illusion tells you you are too high. The potential danger is that you will respond to the illusion rather than the reality and approach too low.

Tilting your hand downward simulates the illusion of the down-slope runway. The illusion is that you are too low and, thus, the potential difficulties arise when we approach the runway with excess altitude. Landing on a down-sloped runway is particularly difficult because, as you flair, the runway drops away and you risk running out of airspeed while still well above the landing surface. Gently does it.

Knowledge, awareness, attitude, and discipline to the rescue. We know the slope because prior to the flight we have investigated the characteristics of our destination aerodrome. We know the illusion will present itself. We can choose to respond to the reality rather than the illusion and execute a safe and accurate landing. It’s just like watching a magic show. We can enjoy an illusion, we can be amused by it, but we don’t have to be fooled into accepting it as real.

Size constancy illusions are a product of runway dimensions.  If we are used to operating out of a runway with particular dimensions, approaching to land on a runway of a different size—wider or narrower, longer or shorter—can induce some complex illusions.

A wider runway gives us the illusion of being too low; a narrower runway induces the illusion of being too high. Due to our experience, our brain has an image of what a runway “should” look like at various altitudes and when faced with a different set of visual inputs can easily interpret the information incorrectly.

Wind, as well, can present some interesting illusions and, once again, it is not the illusion that is the problem. The problem develops when we respond to the illusion rather than the reality.

When flying close to the ground either into or with the wind, we are presented with illusions of speed. With the wind behind us, the illusion we must deal with is that we are traveling at excessive speed; the danger is that we will respond to the illusion and reduce power to slow down, perhaps dangerously approaching stall speed.

With the wind in our face, the illusion is of traveling at too low a speed; the danger is that we will add unnecessary power to counter the illusion and perhaps have excess airspeed that will cause difficulties particularly on landing. This illusion can be particularly apparent and dangerous when on approach into a stiff headwind.

An aircraft flies on airspeed; that’s what we must focus on and trust regardless of the illusion we may be experiencing.

When turning across the wind from into wind to downwind, for example from crosswind to downwind, we are presented with the illusion of slipping. The aircraft is being pushed by the wind relative to the ground toward the direction of the turn. The potential danger is that we may be tempted to add too much inside rudder and actually produce a skid. Remember how you execute a spin entry? From a low speed skid. Yikes. Not such a great idea when flying low and slow.

When turning across the wind from downwind to into wind, for example from base to final, the illusion is that of skid. The wind is carrying the aircraft away from the direction of the turn in relation to the ground. Unfortunately, the typical response to this illusion is also to add too much inside rudder producing the very thing we would like to avoid: a skidding turn at low altitude and low airspeed. It’s a recipe for disaster and has been the cause of more approach accidents than anyone would like to see.

In all of these cases, what happens is quite simple: your eyes and your butt lie to you. Don’t take their word for what is happening. Airspeed is airspeed: go to the source of correct information, your airspeed indicator. The airplane flies on airspeed. For information about slipping and skidding, the little ball on your turn and bank or turn coordinator is the correct source of information, not your eyes or your butt. Act on the reality not the illusion.

Acceleration and deceleration illusions, called somatogravic illusions, can also be very challenging. These illusions tend to present a more difficult problem at night or in limited visibility when we do not have all the other visual clues on which to rely.

Somatogravic illusions are a result of the changes in gravitational vector on our inner ear canals. The semi-circular canals in the ear are filled with fluid that responds to changes in gravitational pull.  Acceleration “...creates a backward inertial force that combines with gravity to produce a resultant gravito inertial vector rotated backward from the pilot... The false climb illusion demonstrates the limitations of the otolith organs in providing accurate information to the brain, when there is insufficient visual information to correct the misinformation” (1).  

When the aircraft accelerates, for example on takeoff, we experience the illusion of pitching up resulting from the effect of that acceleration on the fluid inside our semi-circular canals. The danger is in responding to the illusion and pitching the aircraft’s nose down rather than trusting our airspeed, attitude, and VSI indicators. Some of us are old enough to remember Buddy Holly and the Big Bopper: a classic somatogravic illusion accident.

Understanding illusions is a very important part of being a safe and competent pilot. Knowing them for what they are and training ourselves to respond to reality rather than illusion is a key factor to reducing risk and increasing flight safety. As amusing as they may be, illusions are simply a trick of the senses. Through knowledge, awareness, attitude, and discipline we can avoid being tricked into actions that may prove both embarrassing and dangerous.


1. Lessard, Charles S., et. al., “Visual Scene Effects on the Somatogravic Illusion”