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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.
The Eustachian Tubes are canals that
connect the throat with the middle
Human Factors 407
ear; their purpose is to equalise air
pressure. When you swallow, the
tubes open, allowing air to enter,
which is why swallowing helps to
clear the ears when changing
altitude. Blocked Eustachian tubes
can be responsible for split
eardrums, due to the inability to
equalise pressure. Since the eardrum
takes around 6 weeks to heal, the
best solution is not to go flying with
a cold, but commercial pressures
don't always allow this. If you have
to, make sure you use a decongestant
with no side effects.
The audible range of the human ear
is 20 Hz to 20 KHz.
Blocked Sinuses
Although associated with the
nose, the sinuses are actually
hollow spaces or cavities inside
the head surrounding the base
of the nose and the eye sockets.
Amongst other things, they act
as sound boxes for the voice.
Being hollow, they provide
structural strength whilst
keeping the head light; there are
normally between 15-20.
Blockages arise from fluid that
can't escape through the narrow
passages—pain results from
fluid pressure. Blocked sinuses
can also be responsible for
severe headaches.
Deafness
This can arise from many
causes; in aviation, high-tone
deafness from sustained
exposure to jet engines is very
common. Hearing actually
depends on the proper working
of the eighth cranial nerve, which
carries signals from the inner
ear to the brain. Obviously, if
this gets damaged, deafness
results. The nerve doesn't have
to be severed, though;
deterioration will occur if you
don't get enough Vitamin BComplex
(deafness is a
symptom of beriberi or pellagra,
for example, from Vitamin B
deficiency).
You can recover from some
deafness, such as that caused by
illness, but not that caused by
damage to the fibres in the fluid.
Disorientation
　
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