Flight Training - July 2021 - 51

ADVANCED PILOT AEROMEDICAL FACTORS
THE AIR UP THERE
A BEGINNER'S GUIDE TO OXYGEN USE
BY JILL W. TALLMAN
The cannula is one of the most popular supplemental oxygen delivery methods used in general aviation, because the pilot can wear it while talking or
eating. However, it is less effective than other types of masks, and it can be only used up to 18,000 feet.
EVERY PRIVATE PILOT NEEDS TO KNOW
the essentials of supplemental oxygen
use, but for most of us this important
knowledge doesn't go beyond memorizing
the rules set out in FAR 91.211.
FAR 91.211 requires pilots to use
supplemental oxygen when flying at
cabin pressure altitudes of 14,000 feet
and higher, and for any portion of a flight
at 12,500 to 14,000 feet that exceeds 30
minutes. Above 15,000 feet, all occupants
must use oxygen.
Supplemental oxygen use usually
doesn't come into consideration for
the average GA pilot. You're not flying
high enough, or in an airplane that has a
service ceiling enabling it to fly at higher
altitudes. If you transition to turbine aircraft,
or if you fly in the mountains in an
airplane that can climb higher than 11,500
feet, you'll want to become best friends
with supplemental oxygen equipment.
First, a quick explainer as to why and
when pilots need supplemental oxygen
in a nonpressurized airplane. Some
people say the air at high altitudes gets
" thinner. " The makeup of the atmosphere
doesn't change at any altitude-it
is composed of approximately 21 percent
oxygen and about 78 percent nitrogen.
But the atmospheric pressure does
change. Atmospheric pressure forces
oxygen into your bloodstream through
your lungs' membranes. At higher altitudes,
atmospheric pressure decreases,
and the amount of oxygen forced into
your bloodstream decreases.
Now you need supplemental oxygen
and a delivery system to get that
oxygen into your lungs and into your
bloodstream, lest you suffer the effects
of hypoxia: a range of symptoms
including dizziness, nausea, and even
unconsciousness.
Supplemental oxygen can be delivered
in one of several ways: Continuous
flow, like it sounds, means air flows
continuously to your nose or mouth. It
is a popular portable delivery system for
nonpressurized aircraft, and it can be
used up to 25,000 feet. A typical system
uses a high pressure cylinder and a regulator,
which reduces the oxygen flow to a
lower pressure.
Altitude adjustable systems employ
an adjustable control on their regulators.
This allows the user to dial in the necessary
oxygen flow for the appropriate
altitude.
Altitude compensating systems are
typically not portable. Oxygen flow
changes automatically with changes in
altitude.
Demand systems, designed for
airplanes that can fly up to 35,000 feet,
provide oxygen in short bursts whenever
the pilot inhales. A demand system's
tight-fitting mask has switches that let
the user select between a normal and
a 100-percent oxygen setting. And if
you're going above 35,000 feet, you're
going to look like Tom Cruise in Top
AOPA.ORG/FT
51
CHRIS ROSE

http://www.AOPA.ORG/FT

Flight Training - July 2021

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