Hypoxia
Hypoxia, simply put, is the starving of the body (and brain) of oxygen. To pilots it means a dangerous situation that could turn a good flight very bad. We must do what we can — as pilots and instructors — to keep the dangers of hypoxia to a minimum.
What Hypoxia Does
There is wide variation between people, which creates a large degree of susceptibility to hypoxia. In general, flights below 10,000 MSL in daylight and 7,000 MSL at night do not need supplemental oxygen. The onset of hypoxia is usually slow and does not always have obvious symptoms.
The first reactions are usually: impaired reactions, impaired color vision, confused thinking, poor judgment, unusual fatigue, and a dull headache. These may occur together or one at a time. There is also a possible feeling of “well being”, or euphoria.
As the Aircraft Climbs
Symptoms (and dangers) get worse with altitude. The body gives more signs of impending hypoxia: a tingling feeling on the skin, racing heart, blue lips and nails, fuzzy vision (especially trouble reading small print), and tunnel vision.
The major problem of hypoxia is the pilot’s inability — or disinterest — to correct the problem once it has started. A pilot feeling a sense of well-being and drowsiness is not likely to try to fix it, much like a driver who is impaired yet keeps driving because their poor reasoning tells them everything is fine.
Prevention
Rule of thumb: “Don’t let hypoxia get its foot in the door.” Carry supplemental oxygen and don’t gauge your need by how your body feels — it may be too late by the time you notice.
- Do not fly above 12,000 MSL unless you have supplemental oxygen.
- Use oxygen on all flights above 12,500 MSL — you may not realize you need it, and it’s cheap insurance.
- Use oxygen on flights at night above 7,000 MSL.
- Breathe normally.
- Don’t use lip balm — petroleum and oxygen can spontaneously ignite.
How High Is Too High?
| Altitude | Effect |
|---|---|
| Around 12,500 MSL | Hypoxia typically becomes significant without supplemental oxygen. |
| Above 20,000 MSL | Vision deteriorates — you may not see at all. |
| Above 25,000 MSL | Unconsciousness or possible death. |
Who Is Susceptible?
Everyone. You are more susceptible if you are a smoker, unhealthy, or older — but don’t assume a “healthy non-smoker” can make the flight without oxygen. Never try to prove you can.
Experiencing Hypoxia Safely
The FAA offers aviation physiology training through its Civil Aeromedical Institute and at many military facilities across the United States. The Physiological Training Program lets pilots safely experience hypoxia in a controlled chamber. Contact the Civil Aeromedical Institute, Mike Monroney Aeronautical Center, Oklahoma City, OK, at (405) 954-6212.