Definition
A condition in which the body's tissues, particularly the brain, do not receive enough oxygen to function normally. In aviation, it is most commonly caused by reduced atmospheric pressure at altitude, which lowers the amount of oxygen the lungs can absorb into the bloodstream.
Plain English
Not enough oxygen reaching your body and brain. As you fly higher, the air gets thinner and your body struggles to take in the oxygen it needs, which affects how clearly you can think, see, and react.
Context Anchor
Seen in night flying and human factors discussions, especially when the handbook explains why altitude, fatigue, and oxygen supply affect vision.
Derivation
From Greek 'hypo-' meaning 'under' or 'below,' and '-oxia' from 'oxygen.' Literally 'below-oxygen.' The 'hypo-' prefix is a useful anchor — it shows up in other medical terms like 'hypothermia' (below normal temperature) and signals 'less than enough.'
Why Pilots Care
Hypoxia first degrades night vision and judgment, then coordination and consciousness, creating an immediate safety risk during flight.
Grounding Statement
At night, even a moderate shortage of oxygen can make dim lights and terrain harder to see before the pilot realizes anything is wrong.
Intuition Check
Hypoxia does not always feel like choking or shortness of breath. A pilot can be hypoxic while still breathing normally and feeling confident.
Example Sentence 1
To prevent hypoxia, the pilot began using supplemental oxygen as the flight climbed above 10,000 feet.
Example Sentence 2
Descending promptly to a lower altitude reversed the hypoxia symptoms before they affected control of the aircraft.