Basic Aviation Physiology and Health Maintenance
What the exam tests
Basic Aviation Physiology and Health Maintenance tests the body's response to altitude, pressure change, oxygen and self-medication, and the rules that keep a pilot fit to fly. Expect gas laws, hypoxia, hyperventilation, decompression sickness, barotrauma, vision and fitness or medical limits.
Core rules
- Dalton's law: total pressure is the sum of partial pressures. At altitude, alveolar PO2 falls even though the percentage of oxygen stays 21%.
- Boyle's law: gas volume expands as pressure falls. Trapped gas in ears, sinuses, gut and teeth causes barotrauma; expanding gas during ascent is the greater risk for ears if not vented.
- Henry's law: more gas dissolves in liquid at higher pressure. After diving, nitrogen can come out of solution during flight, causing decompression sickness; follow dive-to-fly intervals.
- Hypoxia signs: euphoria, impaired judgement, cyanosis, headache, fatigue; onset is insidious. Time of useful consciousness at FL350 is roughly 30-60 s after rapid decompression, less with exertion.
- Hyperventilation blows off CO2, causing dizziness, tingling, cramps and vasoconstriction; it can mimic hypoxia. Treatment: control breathing, and if altitude is in doubt, use 100% oxygen and descend.
- Night vision: rods are slow to adapt (20-30 min), poor at colour and detail; use off-centre viewing and avoid bright white light.
Worked example
At FL350 a window seal fails. The pilot feels euphoric and slow. Actions: don oxygen mask immediately, establish communication, descend to FL100 or below. The euphoria is hypoxia, not fatigue; the mask must come before troubleshooting.
Traps
- Treating hyperventilation and hypoxia as mutually exclusive.
- Assuming '21% oxygen' means normal partial pressure at altitude.
- Flying after scuba diving too soon.
- Self-medicating with sedating antihistamines.