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smaller than it actually is, will
also appear to be nearer, and
vice versa. If the object is
brighter than its surroundings (a
well-lit runway), you will think
you are higher than you are, so
on an approach, you might start
early and be lower than you
should. In haze, objects appear
to be further away.
An approach to a downsloping
runway should be started
higher, with a steeper angle, and
one to an upsloping runway
should be started lower, at a
shallower angle.
When mountain flying, it's often
difficult to fly straight and level
because the sloping ground
around affects your judgment.
Similarly, you can't judge your
height when landing on a peak.
Even going to the cinema is an
optical illusion; still frames are
shown so quickly it looks as if
movement is taking place—the
switching is done in the brain.
Vectional illusions are caused by
movement, as when sitting in a
railway carriage and wondering
whether it's the train next to you
or the one you're in that is
moving. The autokinetic effect is
the illusion that an object is
moving, where it is actually your
eye that is moving. Distant
objects become less colourful
and less distinct.
A high speed aircraft
approaching head on will grow
the most in size very rapidly in
the last moments, so it's
possible for an approaching
aircraft to be hidden by a bug
on the windscreen for a high
proportion of its approach time
250 Canadian Private Pilot Studies
(you might only see it in the last
few seconds). Lack of relative
movement makes an object
more difficult to detect.
Ears
These are important because an
auditory stimulus is the one most
often attended to. How many times
do you answer the phone when
you're busy, even though you've
ignored everything else for hours?
Sound waves make the eardrum
vibrate, and the vibrations are
transmitted by a chain of linked
bones known as the hammer, anvil and
stirrup to the inner ear, which is full
of fluid. There are thousands of
fibres of different lengths within the
inner ear which vibrate in sympathy
according to different frequencies.
As some of the fibres get damaged
(through too severe vibration), the
ability to hear that frequency goes
(they do not regenerate). Presbycusis is
hearing loss with age, where the high
tones go first. Noise Induced Hearing
Loss, or NIHL, occurs through
prolonged exposure to loud noise,
usually 90 db and above. The fibres
are linked to the brain and, as with
sight, it is now, when the signal
reaches the brain, that we "hear".
The semicircular canals are what we use
to keep balanced:
They use the fluid in the inner ear,
which acts against sensors to send
electrical signals to the brain so you
can tell which way up you are (they
detect angular acceleration). The
leans happen because your
semicircular canals get used to a
particular sustained motion in a very
short time. If you start a turn and
keep it going, your canals will think
this is normal, because they lag, or
are slow to respond. When you
straighten up, they will try to tell you
you're turning, where you're actually
flying straight and level. Your natural
inclination is to obey your senses,
but your instruments are there as a
cross-reference. In fact, the whole
point of Instrument Training is to
overcome your dependence on your
senses. Particularly dangerous is
recovering from a spin of 2-3 turns,
where you think you are actually
turning the opposite way and enter
another spin when you try to correct
it. Eventually an extreme nose-up
condition results, which turns into
an extreme nose-down attitude and a
tight graveyard spiral before entering
Terrain Impact Mode.
The coriolis illusion is easily
demonstrated with a revolving chair
– sit in one, and get someone to spin
it while you have your chin on your
breast. When you raise your head
sharply, you will find yourself on the
floor inside two seconds. This has
obvious parallels with flying, so
make all your head movements as
gently as possible, especially when
making turns or other manoeuvres
in IMC.
You can get problems from colds,
etc as well, particularly a spinning
sensation caused by a sudden
difference in pressure between the
inner portions of each ear.
Human Factors 251
The Eustachian Tubes are canals that
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