Human Factors
Core content
Human factors examines how people interact with aircraft, tools, procedures and each other. The SHELL model describes software, hardware, environment and liveware, with the central liveware representing the person. You should understand error types: slips, lapses, mistakes and violations. Fatigue, stress, complacency, distraction, pressure, lack of resources and poor communication are recognised contributors. Situational awareness, decision making, teamwork, leadership and assertiveness are core skills. Vision and hearing change with age and environment, and circadian rhythms affect alertness. A just culture encourages reporting without punishing honest error, while still holding people accountable for reckless acts.
Traps
Do not treat complacency as a root cause; it is usually a symptom of repeated success and low perceived risk. Distinguish an error from a violation: a violation is a deliberate deviation from a rule or procedure. Fatigue is not simply tiredness; it impairs reaction time, memory and judgement, and cannot be overcome by motivation. Another trap is assuming more communication is always better: communication must be clear, timely and confirmed. Also remember that stress can improve performance at low levels but degrades it at high levels.
Worked example
A technician working a second consecutive night shift is asked to sign off a complex avionics modification. The correct response is to recognise fatigue risk, use the checklist, request an independent cross-check, and defer non-urgent tasks if possible. Rule of thumb: when fatigue or pressure is high, increase verification rather than relying on memory.
Key points
- SHELL links software, hardware, environment and liveware.
- Slips and lapses are skill-based; mistakes are judgement-based.
- A violation is a deliberate deviation from a rule.
- Fatigue impairs memory, reaction time and judgement.
- Cross-checking and checklists reduce error under pressure.