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company personnel) should be
conducted as per the Ops Manual.
Non-Passenger
When no passengers are carried, as
with training, air tests, delivery,
demonstration or empty positioning
flights, you must still follow the Ops
Manual, except that you don't need
to raise a mass and balance
document if remaining within the
appropriate limits, and neither do
you need licensed aerodromes (in
the UK, except for training),
provided performance and minima
requirements can be met.
Oxygen Requirements
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 supports combustion, which
is why we need it so much, because
the body turns food into heat
energy. 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
for quite a long way up, but as the air
gets less dense, each lungful contains
less oxygen in proportion (that is,
the partial pressure becomes less),
which is why high altitude flight
requires extra supplies. Nothing
more is required below 5000’, as
95% of what you would find on the
ground can be expected there.
However, at over 8000’, you may
find measurable changes in blood
pressure and respiration, although
healthy individuals should be OK.
As you creep up to 10,000 feet, the
symptoms of oxygen deficiency
(otherwise known as Hypoxia), that
is, impairment of vision (especially at
night), lassitude, drowsiness, fatigue,
sharp headaches and a false feeling
of well-being, can catch you
unawares. The intensity varies from
person to person according to
altitude, the exposure and amount of
exercise being undergone—the more
energy expended, the more severe
the symptoms. If they occur without
obvious cause, suspect Hypoxia (or
hyperventilation, described below)
and either descend or use
supplemental oxygen. It's important
to use it before the onset of
Hypoxia, because the condition itself
makes you think you don’t need it,
but if you’re flying high and get rapid
decompression, you may become
134 Operational Flying
unconscious before symptoms occur
– at 50,000 feet, you have about a
minute. You may get some
symptoms as low as 8000’, but these
are considered acceptable. There’s
more about this in the CRM chapter.
As mentioned above, Hypoxia
means lack of oxygen, whether
because there really is too little, or
because 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. A blockage of 5-8%,
typical for a heavy smoker, gives you
the equivalent altitude of 5-7000 feet
before you start!
Hyperventilation is breathing too
quickly, but the effect is not to
increase the blood’s oxygen content,
but decrease the carbon dioxide
level, making the blood more
alkaline so the blood vessels get
constricted, hence less oxygen to the
brain and maybe a headache.
The oxygen to be carried, and the
people to whom masks should be
made available, varies with altitude,
rate of descent and MSA. The latter
two are dependent on each other, in
that it's no good having a good rate
of descent if the MSA stops you. It
may well be that, although you're
flying at a level that requires fewer
masks, the MSA may demand that
you equip everybody.
Preflight stuff includes ensuring that
oxygen masks are accessible for the
crew, and that passengers are aware
of where their own masks are. Check
the security of the circular dilution
valve filter (a foam disc) on all of
them, together with the pressure.
Beards will naturally reduce their
efficiency. Briefings should include
the importance of not smoking and
monitoring the flow indicator. All
NO SMOKING signs should be on
when using it.
Non-pressurised Aeroplanes
Non-pressurised aeroplanes must
not go above 10 000 feet without
masks and supplies for:
· all the flight crew above 10 000
feet PA, for the whole time over
30 minutes between 10-13,000'.
· the cabin crew when above 13
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