Human Performance and Limitations
What the exam tests
Human performance tests hypoxia, vision, spatial disorientation, fatigue, stress, decision-making, CRM and error models.
Core concepts
- Time of useful consciousness: about 3–5 min at FL250, 1–2 min at FL300, 30–60 s at FL350 and 15–20 s at FL400.
- Hypoxia symptoms include euphoria, cyanosis, impaired judgement and tunnel vision; hyperventilation causes dizziness and tingling but not cyanosis.
- Spatial disorientation: the somatogravic illusion during acceleration feels like a climb; the leans follow a slow roll.
- Vision: cones for colour and acuity in the fovea; rods for night vision, needing about 30 min dark adaptation.
- Fatigue is cumulative; circadian low points are around 03:00–05:00 and 15:00–17:00.
- The SHELL model and Swiss-cheese error model explain how latent conditions combine with active failures.
Worked example
A rapid decompression at FL380 gives roughly 15–20 s of useful consciousness. The first actions are oxygen mask on, establish communication, then emergency descent to 10,000 ft or the minimum safe altitude.
Traps
Confusing hypoxia with hyperventilation; assuming oxygen removes all fatigue; and forgetting that the somatogravic illusion is most dangerous on takeoff and go-around.