HYPOXIA

The Higher You Fly...

The Less Air In The Sky

BRIEFLY...

• When you breathe, you inhale oxygen and exhale 

carbon dioxide.

• With each normal breath, you inhale about onehalf 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.

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

OK-20-0926 4/29/2020
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 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.