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Ground School: Hypoxia

This introduction to hypoxia is excerpted from the FAA’s Pilot’s Handbook of Aeronautical Knowledge, available from ASA.

Hypoxia means “reduced oxygen” or “not enough oxygen.” Although any tissue will die if deprived of oxygen long enough, usually the most concern is with getting enough oxygen to the brain, since it is particularly vulnerable to oxygen deprivation. Any reduction in mental function while flying can result in life-threatening errors. Hypoxia can be caused by several factors, including an insufficient supply of oxygen, inadequate transportation of oxygen, or the inability of the body tissues to use oxygen.

Symptoms of Hypoxia
Oxygen starvation causes the brain and other vital organs to become impaired. One noteworthy attribuite of the onset of hypoxia is that the first symptoms are euphoria and a carefree feeling. With increased oxygen starvation, the extremities become less responsive and flying becomes less coordinated. The symptoms of hypoxia vary with the individual, but common symptoms include:

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  • Cyanosis (blue fingernails and lips)
  • Headache
  • Decreased reaction time
  • Impaired judgment
  • Euphoria
  • Visual impairment
  • Drowsiness
  • Lightheaded or dizzy sensation
  • Tingling in fingers and toes
  • Numbness

As hypoxia worsens, the field of vision begins to narrow, and instrument interpretation can become difficult. Even with all these symptoms, the effects of hypoxia can cause a pilot to have a false sense of security and be deceived into believing everything is normal. The treatment for hypoxia includes flying at lower altitudes and/or using supplemental oxygen.

All pilots are susceptible to the effects of oxygen starvation, regardless of physical endurance or acclimatization. When flying at high altitudes, it is paramount that oxygen be used to avoid the effects of hypoxia. The term “time of useful consciousness” describes the maximum time the pilot has to make rational, life-saving decisions and carry them out at a given altitude without supplemental oxygen. As altitude increases above 10,000 feet, the symptoms of hypoxia increase in severity, and the time of useful consciousness rapidly decreases.

Time of useful consciousness.

Time of useful consciousness.

Since the symptoms of hypoxia can be different for each individual, the ability to recognize hypoxia can be greatly improved by experiencing and witnessing the effects of it during an altitude chamber “flight.” The FAA provides this opporotunity through aviation physiology training, which is conducted at the FAA Civil Aerospace Medical Institute (CAMI) and at many military facilities across the United States. For information about the FAA’s one-day physiology training course with altitude chamber and vertigo demonstrations, visit the FAA Aerospace Physiology Training website (a link to the CAMI enrollment application can be found here).

More information about aeromedical factors, including physiological factors affecting pilot performance, can be found in the FAA’s Pilot’s Handbook of Aeronautical Knowledge, available from ASA.

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