Human Performance and Limitations
Human Performance and Limitations tests physiology, sensory illusions, fatigue, stress, decision-making and crew cooperation. The examiner wants practical recognition and response, not lists of symptoms alone.
Hypoxia and hyperventilation
Hypoxic hypoxia occurs when oxygen partial pressure falls with altitude; symptoms include euphoria, poor judgement, headache, cyanosis and impaired vision. Hyperventilation lowers carbon dioxide and causes dizziness, tingling, cramps and a feeling of breathlessness. Both can occur together. If hypoxia is suspected at altitude, use oxygen and descend; do not diagnose from the ground.
Spatial disorientation
The leans, somatogravic illusion and black-hole approach all occur when the senses conflict with instruments. In a black-hole approach over dark water or unlit terrain, the pilot may fly too low. Trust the flight instruments and use a published glidepath, PAPI or ILS.
Fatigue and decision-making
Fatigue impairs vigilance, reaction time and judgement. Circadian disruption, sleep debt, alcohol and some medicines increase risk. Use checklists, set personal limits, and apply crew resource management: brief, monitor, speak up and cross-check.
Worked example
On a night VFR approach to a runway with few lights and dark terrain before the threshold, the pilot feels high and descends. The illusion is a black-hole effect: the lack of visual cues makes the aircraft seem higher than it is. The correct response is to maintain the instrument or published glidepath, use PAPI or ILS, and not chase the picture outside.
Traps
Assuming hyperventilation is always harmless; ignoring carbon monoxide from a heater; believing experience prevents disorientation; pressing on with fatigue because the flight is short.