Human Factors: Performance, Error and the Maintenance Environment
The SHELL and Dirty Dozen frameworks
Human factors questions test whether you can link a concept to a realistic maintenance scenario. Understand the SHELL model (Software, Hardware, Environment, Liveware) and how mismatches at the interfaces create error. Learn the Dirty Dozen (fatigue, complacency, distraction, lack of communication, lack of resources, pressure, lack of assertiveness, stress, lack of awareness, norms, lack of knowledge, teamwork) and be able to match each to an example.
Performance limitations
Know the effects of fatigue (circadian rhythm, cumulative sleep debt, reduced vigilance), stress (optimum arousal versus overload), and noise, temperature and lighting on task performance. Understand the limits of memory and how checklists, placards and task cards compensate; understand complacency after repetitive tasks and the role of independent inspection.
Error and violation
Distinguish slips and lapses (skill-based), mistakes (rule- or knowledge-based) and violations (routine versus exceptional). Understand a just culture: reporting is encouraged, but reckless behaviour is still accountable. Know the purpose of the MEDA-style maintenance error investigation model.
Traps
- Assuming more stress always improves performance; the Yerkes-Dodson curve shows an optimum.
- Confusing a violation with an error; the intent differs.
- Forgetting that communication failure includes shift handover, not just radio calls.
Rule of thumb
For any scenario, name the interface (S-H, S-L, H-L, L-L, or L-E) and the Dirty Dozen element at play; that framing usually identifies the answer.