Basic Aviation Physiology and Health
This domain tests how the body responds to altitude, pressure change and the cabin environment: hypoxia, hyperventilation, trapped gas, decompression sickness and common health threats such as carbon monoxide and alcohol. The exam expects applied recognition and immediate action, not deep physiology.
Hypoxia
- Hypoxic hypoxia begins when alveolar oxygen partial pressure falls with altitude. Effects are insidious: euphoria, poor judgement, tunnel vision, cyanosis and eventually unconsciousness.
- Approximate time of useful consciousness (TUC): FL180 about 20–30 minutes, FL250 3–5 minutes, FL350 30–60 seconds, FL400 15–20 seconds. Cold, exertion and illness shorten it.
- Treat suspected hypoxia with 100% oxygen and descent. Do not wait to confirm the diagnosis.
Pressure and gas laws
- Boyle's law: trapped gas expands as cabin altitude climbs and contracts on descent, causing ear, sinus, dental and gut barotrauma.
- Dalton's law: each gas exerts a partial pressure; Henry's law: dissolved nitrogen comes out of solution when pressure falls rapidly, causing decompression sickness.
- Equalise early and often; do not fly with a severe cold or sinus block.
Other health threats
- Carbon monoxide binds haemoglobin far more strongly than oxygen; headache, confusion and tachycardia occur, and a pulse oximeter can read falsely normal.
- Alcohol, recreational drugs and some medications impair judgement and worsen hypoxia; dehydration and fatigue compound the effect.
Worked example
A pilot at FL350 becomes euphoric, stops scanning and feels warm. Hypoxia is the default explanation at that altitude. The correct response is oxygen first and descent, not troubleshooting. At FL350 the TUC may be under a minute, so any delay risks unconsciousness.
Traps that cost marks
- Confusing hyperventilation with hypoxia: both cause dizziness and tingling, so give oxygen anyway.
- Assuming a normal oximeter excludes carbon monoxide.
- Forgetting that gas expands on climb and must be equalised on descent.