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Instrument Flying Handbook
Human factors
Optical illusions

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Instrument Flying
Handbook

Preface

Table of Contents

Chapter 1. Human Factors
Chapter 2. Aerodynamic Factors
Chapter 3. Flight Instruments
Chapter 4. Section I
Airplane Attitude Instrument
Flying
Using Analog Instrumentation
Chapter 4. Section II
Airplane Attitude Instrument
Flying
Using an Electronic Flight
Display

Chapter 5. Section I
Airplane Basic
Flight Maneuvers
Using Analog Instrumentation
Chapter 5. Section II
Airplane Basic
Flight Maneuvers
Using an Electronic Flight
Display

Chapter 6. Helicopter
Attitude Instrument Flying

Chapter 7. Navigation Systems
Chapter 8. The National
Airspace System

Chapter 9. The Air Traffic
Control System

Chapter 10. IFR Flight
Chapter 11. Emergency
Operations

Most importantly, become proficient in the use of
flight instruments and rely upon them. Trust the
instruments and disregard your sensory perceptions.

The sensations that lead to illusions during instrument
flight conditions are normal perceptions experienced by
pilots. These undesirable sensations cannot he completely
prevented, but through training and awareness, pilots can
ignore or suppress them by developing absolute reliance
on the flight instruments. As pilots gain proficiency in
instrument flying, they become less susceptible 10 these
illusions and their effects.

Optical ilusions

Of the senses, vision is the most important for safe flight.
However, various terrain features and atmospheric conditions
can create optical illusions. These illusions are primarily
associated with landing. Since pilots must transition from
reliance on instruments to visual cues outside the flight
deck for landing at the end of an instrument approach, it is
imperative they he aware of the potent al problems associated
with these illusions, and take appropriate corrective action.
The major illusions leading to landing errors are described
below.

Runway Width Illusion
A narrower-than-usual runway can create an illusion the
aircraft is at a higher altitude than it actually is, especially
when runway length-to-width relationships are comparable.
[Figure 1-94] The pilot who does not recognize this illusion
will fly a lower approach, with the risk of striking objects
along the approach path or landing short. A wider-than-usual
runway can have the opposite effect, with the risk of leveling
out high and landing hard, or overshooting the runway.

Runway and Terrain Slopes Illusion
An upsloping runway, upsloping terrain, or both, can create
an illusion the aircraft is at a higher altitude than it actually
is. [Figure J-9B/ The pilot who does not recognize this
illusion will fly a lower approach. Downsloping runways and
downsloping approach terrain can have the opposite effect,

Featureless Terrain Illusion
An absence of surrounding ground features, as in an
over water approach, over darkened areas, or terrain made
featureless by snow, can create an illusion the aircraft is at
a higher altitude than it actually is. This illusion, sometimes
referred to as the "black hole approach," causes pilots to fly
a lower approach than is desired.

Water Refraction
Rain on the windscreen can create an illusion of being at a
higher altitude due to the horizon appearing lower than it is.
This can result in the pilot flying a lower approach.

Haze
Atmospheric haze can create an illusion of being at a greater
distance and height from the runway. As a result the pilot
will have a tendency to be low on the approach. Conversely,
extremely clear air (clear bright conditions of a high attitude
airport) can give die pilot the illusion of being closer than he
or she actually is, resulting in a high approach, which may
result in an overshoot or go around. The diffusion of light
due to water particles on the windshield can adversely affect
depth perception. The lights and terrain features normally
used to gauge height during landing become less effective
for the pilot.

Fog
Flying into fog can create an illusion of pitching up. Pilots
who do not recognize this illusion will often steepen the
approach quite abruptly.

Ground Lighting Illusions
Lights along a straight path, such as a road or lights on moving
trains, can be mistaken for runway and approach lights. Bright
runway and approach lighting systems, especially where
few lights illuminate the surrounding terrain, may create the
illusion of less distance to the runway. The pilot who does not
recognize this illusion will often fly a higher approach.

How To Prevent Landing Errors Due to
Optical Illusions

To prevent these illusions and their potentially hazardous
consequences, pilots can:
I. Anticipate the possibility of visual illusions during
approaches to unfamiliar airports, particularly at
night or in adverse weather conditions. Consult
airport diagrams and the Airport Facility Directory
(AFD) for infonnation on runway slope, terrain, and
lighting.
2. Make frequent reference to the altimeter, especially
during all approaches, day and night.
3. If possible, conduct aerial visual inspection of
unfamiliar airports before landing.

 

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