Lack of oxygen is the
greatest single danger to man at high altitudes, despite the importance
of pressure and temperatures. The shortage of oxygen in the human body
results in a condition called hypoxia, which simply means oxygen
starvation. When a pilot inhales air at high altitudes, there isn't
enough oxygen pressure to force adequate amounts of this vital gas
through the membranes of the lungs into the blood stream, so that it can
be carried to the tissues of the body. The function of various organs,
including the brain, is then impaired.
nature of hypoxia makes you, the pilot, the poorest judge of when you
are its victim. The first symptoms of oxygen deficiency are misleadingly
pleasant, resembling mild intoxication from alcohol. Because oxygen
starvation strikes first at the brain, your higher faculties are dulled.
Your normal self-critical ability is out of order. Your mind no longer
functions properly; your hands and feet become clumsy without being
aware of it; you may feel drowsy, languid, and nonchalant; you have a
false sense of security; and, the last thing in the world you think you
need is oxygen.
As the hypoxia gets
worse, you may become dizzy or feel a tingling of the skin. You might
have a dull headache, but you are only half aware of it. Oxygen
starvation gets worse the longer you remain at a given altitude, or if
you climb higher. Your heart races, your lips and the skin under the
fingernails begin to turn blue, your field of vision narrows, and the
instruments start to look fuzzy. But hypoxia - by its nature, a grim
deceiver - makes you feel confident that you are doing a better job of
flying than you have ever done before. You are in about the same
condition as the fellow who insists on driving his car home from a New
Year's Eve party when he can hardly walk. Regardless of his
acclimatization, endurance, or other attributes, every pilot will suffer
the consequences of hypoxia when he is exposed to inadequate oxygen
What do you do about
it? There is one general rule: Don't let hypoxia get a foot in the
door. Carry oxygen and use it before you start to become hypoxic. Don't
gauge your "oxygen hunger" by how you feel. Gauge it by the altimeter.
Here are some general
suggestions which apply to young healthy flyers.
1. Carry oxygen in your plane or don't fly above 12,500 feet. If bad
weather lies ahead, go around it if you can't get over it.
2. Use oxygen on every flight above 12,500 feet. You'll probably
need it, and when you do, you might not realize it.
3. Use oxygen on protracted flight near 12,500 feet. It won't hurt
you and you'll be a lot sharper pilot.
4. Use oxygen on all night flights above 5,000 feet. If you want to
give your night vision the best protection, use oxygen from the ground
5. Breathe normally when using oxygen. Rapid or extra deep
breathing can cause loss of consciousness also. (See Chapter 5,
Flying above 12,500 feet
without using oxygen is like playing Russian roulette - the odds are
than you may not get hurt, but it's a deadly game! At 20,000 feet your
vision deteriorates to the point that seeing is almost impossible. The
engine sounds become imperceptible, breathing is labored, and the heart
beats rapidly. You haven't the vaguest idea what is wrong, or whether
anything is wrong. At 25.000 feet you will collapse and death is
imminent unless oxygen is restored.
No one is exempt from
the effects of hypoxia. Everyone needs an adequate supply of oxygen.
Some pilots may be able to tolerate a few thousand feet more of altitude
than some others, but no one is really very far from average. Remember
this: Serious trouble is waiting for the pilot who tries to test
himself to prove how much higher he can fly or how much longer he can
function without supplemental oxygen. Pilots who are older, fatter, out
of condition, or smoke heavily should limit themselves to a ceiling of
8,000 to 10,000 feet unless oxygen is available.
Many executive aircraft
now have pressurized cabins and regularly operate up to 40,000 feet.
Most of these aircraft are equipped with pressure-breathing oxygen
systems which provide a supply of oxygen under a slight pressure. In
case of a loss of cabin pressure at altitudes in excess of 38,000 feet,
the oxygen pressure within the lungs cannot be maintained without an
increase in the inhaled oxygen pressure, therefore, hypoxia will develop
rapidly. The addition of positive pressure to pure oxygen is necessary
in order to restore the body to a non-hypoxic state. Pressure breathing
includes the reverse of the normal respiratory cycle, in that the lungs
must perform work during exhaling instead of inhaling. Although pressure
breathing can increase a pilot's tolerance to higher altitudes, it
should not be considered for routine flights. The pressure-breathing
installation is a back-up system only and should be reserved for the
occasion when cabin pressurization fails. Oxygen would then be available
during descent to lower altitudes where it would not be required.