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to get the impression of
pitching up, making you want to
push the nose down (it's more
pronounced at night going into
a black hole from a well-lit
area). You get a pitch-down
illusion from deceleration. The
244 JAR Private Pilot Studies
danger here is that lowering the
gear or flaps causes the machine
to slow down, which makes you
think you are pitching down and
want to bring the nose up,
which could cause a stall at the
wrong moment on approach.
Respiratory System
Consists of the lungs, oronasal
passage, pharynx, larynx, trachea,
bronchi, bronchioles and alveoli:
Air is drawn into the lungs, from
where oxygen is diffused into the
haemoglobin in the blood under
pressure, which carries it to the
tissues of the body, especially the
brain, the most sensitive to lack of it.
Blood is pumped around by the
heart. Waste products in the form of
carbon dioxide go the other way, via
plasma to the lungs (it is the carbon
dioxide level in the blood that
regulates respiration, which is
monitored by chemical receptors in
the brain that are very sensitive to
CO2). The diffusion of oxygen into
the blood depends on partial pressure
(that is, the pressure in proportion to
the amount of an individual gas in
the mix), so as this falls, oxygen
assimilation is impaired (although
the air gets thinner, the ratio of gases
remains the same). Even if you
increase the proportion of oxygen to
100% as you climb, there is an
altitude (around 33,700 feet) where
the pressure is so low that the partial
pressure is actually less than that at
sea level, so just having oxygen is
not enough.
From 0-10,000 ft you can survive on
normal air; above this, an increasing
amount of oxygen relative to the
other ingredients is required, up to
33,700 feet, at which point you
require pure oxygen to survive
(breathing 100% oxygen at that
height is the same as breathing air at
sea level. At 40,000' it is the
equivalent of breathing air at 10,000
feet). Above 40,000 the oxygen
needs pressure (also, exposure to 03
becomes significant). Having said all
that, your learning ability can be
compromised as low as 6000 feet
(Source: RAF).
The normal rate of breathing is
around 18 times a minute,
exchanging .35-.65 litres of air.
Oxygen
Pure oxygen is a colourless, tasteless,
odourless and non-combustible gas
that takes up about 21% of the air
we breathe. Although it doesn't burn
itself, it does support combustion,
which is why we need it, because the
body turns food into heat. As we
can't store oxygen, we survive from
breath to breath.
How much you use depends on your
physical activity and/or mental
stress—for example, you need 4
times more for walking than sitting
quietly. The proportion of oxygen to
air (21%) actually remains constant,
but as the air gets less dense, each
lungful contains less oxygen in
Human Factors 245
proportion (that is, the partial pressure
becomes less), which is why high
altitude flight requires extra supplies.
Nothing more is required below
5000 feet, as 95% of what you would
find on the ground can be expected
there. However, at over 8000 feet,
you may find measurable changes in
blood pressure and respiration,
although healthy individuals should
perform satisfactorily.
Lack of oxygen leads to...
Hypoxia
A condition where you don't have
enough oxygen in the tissues,
resulting from inefficient transfer of
it into the blood, but anaemia can
produce the same effect, as can
alcohol (there are actually several
types of hypoxia, but we won’t
bother with that here). In other
words, there may really be too little
oxygen, or you don’t have enough
blood to carry what you need around
the body—you may have donated
some, or have an ulcer. You might
also be a smoker, with your
haemoglobin blocked by carbon
monoxide (anaemic hypoxia). A
blockage of 5-8%, typical for a heavy
smoker, gives you the equivalent
altitude of 5-7000 feet before you
even start!
The effects of hypoxia are similar to
alcohol but the classic signs are:
· Personality changes. You get jolly,
aggressive and less inhibited.
· Judgement changes. Your abilities
are impaired; you think you are
capable of anything and have
much less self-criticism.
· Muscle movement. Becomes
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