FAA Brochure - Hypoxia

HYPOXIABRIEFLY…

• When you breathe, you inhale oxygen and exhale

carbon dioxide.

• With each normal breath, you inhale about one-

half liter of air, 20% of which is oxygen.

• At 18,000’ MSL, you have half the sea level air

pressure; hence, only half the oxygen.

• Oxygen starvation first affects the brain; judgment

is impaired, so you may not know you are in

trouble.

• We all react differently to the effects of hypoxia.

Only physiological training can safely “break the

code” for you.

PHYSIOLOGICAL TRAINING

CLASSES FOR PILOTS

The effects of hypoxia can be safely experienced

under professional supervision at the Civil

Aeromedical Institute (CAMI) in Oklahoma City, or at

selected WINGS hypoxia demonstration events.

If you are interested in taking a one-day aviation

physiological training course with altitude chamber

and vertigo demonstrations or a one-day survival

course, learn about how to sign up for these courses

that are offered CAMI by visiting this FAA Web site:

https://www.faa.gov/go/aerophys

You’ll learn to recognize your symptoms of hypoxia. It

could mean the difference between life and death.

The Higher You Fly…

The Less Air In The Sky

OK-24-1154 9/18/2024

Provided by

Aerospace Medical Education Division, AAM-400

To obtain copies of this brochure online:

https://www.faa.gov/pilots/safety/

pilotsafetybrochures/

or contact:

Federal Aviation Administration

Civil Aerospace Medical Institute

AAM-400

P.O. Box 25082

Oklahoma City, OK 73125

(405) 954-4831

Breathing is one of the most automatic things we

do – over 20,000 times a day. Each breath does two

things for our body. It expels carbon dioxide when we

exhale, and takes in oxygen when we inhale. It’s a

delicate balance.

Exercise or stress increases the production of carbon

dioxide so we breathe faster to eliminate it and take in

more oxygen at a greater rate.

Because of the effects of gravity, the amount of air

containing oxygen is greater at sea level. For example, the

pressure at sea level is twice that found at 18,000 feet

mean sea level (MSL).

Although the percentage of oxygen contained in air at

18,000 feet is identical to that at sea level (a little over

20%), the amount of air our lungs take in with each

breath contains half the oxygen found at sea level.

Breathing faster or more deeply doesn’t help. In fact,

because you’re consciously over-riding a system that is

normally automatic, you’ll be compounding the problem

by exhaling too much carbon dioxide.

SUPPLEMENTAL OXYGEN

For Part 91 General Aviation operations the required

flight crew must use supplemental oxygen for any

portion of the flight that exceeds 30 minutes above a

cabin pressure altitude of 12,500 feet mean sea level

MSL up to and including 14,000 feet MSL. The flight

crew must use supplemental oxygen for the entire

duration of flight operations above a cabin pressure

altitude of 14,000 feet MSL (14 CFR § 91.211).

In Part 135 Commuter and On Demand or Part 121 Air

Carrier operations in unpressurized aircraft the required

minimum flight crew must use supplemental oxygen

for that part of the flight that exceeds 30 minutes above

10,000 feet through 12,000 feet MSL. Above 12,000

feet MSL each member of the flight deck crew must use

supplemental oxygen during the entire portion of the

flight at those altitudes (14 CFR § 135.89, § 135.157, §

121.327, & § 121.329).

For best protection, you are encouraged to use

supplemental oxygen above 10,000 feet MSL.

At night, because vision is particularly sensitive to

diminished oxygen, a prudent rule is to use supplemental

oxygen when flying above 6,000 feet MSL.

So, when you fly at high altitudes, supplemental oxygen

is the only solution. That’s because supplemental oxygen

satisfies the twin demands of having enough oxygen

to meet your body’s demands and a breathing rate that

excretes the right amount of carbon dioxide.

HYPOXIA

Unfortunately, our body doesn’t give us reliable signals

at the onset of hypoxia – oxygen starvation – unless

we have received special training to recognize the

symptoms. In fact, it’s quite the contrary. The brain is

the first part of the body to reflect a diminished oxygen

supply, and the evidence of that is usually a loss

of judgment.

HYPOXIA TESTS

Altitude chamber tests, in which high altitude flight

conditions are duplicated, have shown that some people

in an oxygen deficient environment actually experience

a sense of euphoria – a feeling of increased well-being.

These subjects can’t write their name intelligibly, or even

sort a deck of cards by suits…yet, they think they’re

doing just fine!Such is the insidious nature of oxygen deprivation. It

sneaks up on the unwary and steals the first line of

sensory protection – the sense that something is

wrong – dreadfully wrong.

THE HIGHER YOU GO

Bear in mind, the progressive reduction of oxygen

per breath will continue the higher you go. Flying

above a layer of clouds that doesn’t look too high, or

flying in the mountains on a clear day – are the very

environments that have caused many good “flat-land”

pilots to get into trouble.

SYMPTOMS

Everyone’s response to hypoxia varies. Unless, as

we’ve stated, you’ve had special training to recognize

its symptoms, hypoxia doesn’t give you much warning.

It steals up on you, giving your body subtle clues.

The order of symptoms varies among individuals:

increased breathing rate, headache, lightheadedness,

dizziness, tingling or warm sensations, sweating,

poor coordination, impaired judgment, tunnel vision,

and euphoria. Unless detected early and dealt with,

hypoxia can be a real killer.

CAUTION AND SAFETY

So, don’t decide you’ll try to fly over that range of

mountains, thinking you’ll turn back if you start to

feel badly. You may feel great…until it’s too late! Use

supplemental oxygen.

SMOKING AND ALTITUDE

A Western state pilot lived to tell about this one.

Cruising at 13,500 feet MSL over mountainous terrain

in his light single, he took a deep drag on his cigarette

and next remembered being in a screaming dive with

just enough altitude left in which to pull out! That

deep drag replaced precious oxygen in his brain with

carbon monoxide…and he passed out.