Aeromedical factorsQuestion 709 of 934

A pilot climbs to a high altitude. Why does hypoxic hypoxia occur?

  1. Oxygen partial pressure falls as altitude increases
  2. The percentage of oxygen in the air falls with altitude
  3. Carbon dioxide replaces oxygen in the air at altitude
  4. Nitrogen in the air blocks the hemoglobin in the blood
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Correct answer: Oxygen partial pressure falls as altitude increases

The percentage of oxygen stays the same, but the partial pressure falls as atmospheric pressure decreases.

Source: Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Chapter 17: Aeromedical Factors — Hypoxic Hypoxia, page 425

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Questions last reviewed: 18 October 2026