Human Factors and Maintenance Resource Management
This domain tests why competent mechanics still make errors, and what systems and habits reduce them. Questions often present a scenario and ask for the best barrier, not the best intention.
Models to know
- SHELL model: Software, Hardware, Environment and Liveware interact; most errors occur at the Liveware interfaces.
- The Dirty Dozen: lack of communication, complacency, lack of knowledge, distraction, lack of teamwork, fatigue, lack of resources, pressure, lack of assertiveness, stress, lack of awareness, and norms.
- Reason's Swiss cheese model: active failures at the sharp end pass through holes created by latent conditions such as poor procedures, high workload, or weak supervision.
- Error types: slips and lapses are execution errors; mistakes are planning errors; violations are deliberate deviations.
Practical barriers
Briefings, read-back communication, task interruption registers, torque stripes, independent inspections, shift handover checklists, and a just culture that encourages reporting all reduce error. Fatigue degrades vigilance and recall; a 12-hour shift is a risk factor, not a badge of commitment.
Worked example
A mechanic is torqueing an engine oil line when called away. He returns, believes he has already torqued the fitting, and signs the task off. The line leaks on the next flight. The active failure is the missed torque; the latent conditions are the interruption, no torque stripe, and no independent check. The best fix is a combination: mark torqued fasteners, record interruptions, and require an independent inspection of critical fittings.
Traps that cost marks
- Blaming the individual only, ignoring the system that allowed the error.
- Treating complacency as a personality flaw rather than a risk state.
- Assuming a just culture means no accountability.
- Confusing a mistake with a violation.