What are human factors?
Human factors is the study of how people interact with systems, tools, procedures and one another, and how those interactions influence safety and performance. In maintenance, most incidents are not caused by a lack of technical skill but by predictable human limitations — fatigue, distraction, poor communication — acting at the wrong moment. Recognising these limitations is the first step to defending against them.
The Dirty Dozen
The “Dirty Dozen” names twelve of the most common preconditions for maintenance error: 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 (unwritten habits that drift away from proper procedure). None of these is exotic; each is an everyday state that, unmanaged, can lead to an error such as an incomplete reassembly or an overlooked inspection.
Why it matters
History is full of accidents whose root cause was a maintenance human-factors failure rather than a mechanical one — a fastener left loose, a task interrupted and never completed, a verbal handover that lost critical detail. Understanding the Dirty Dozen turns these from mysterious “human error” into recognisable, preventable patterns.
Building safety nets
The response is not to demand perfection but to design against error. Countermeasures include thorough shift handovers and documentation, independent inspections of critical tasks, realistic workload and fatigue management, a culture where anyone can raise a concern, and disciplined use of checklists so that pressure and distraction do not translate into missed steps. Good organisations treat these safety nets as seriously as any tool in the hangar.
Where it fits in your licence
Human factors is a formal part of the CAR-66 and EASA Part-66 syllabus (Module 9), and for good reason: it is examined because it saves lives. Internalising the Dirty Dozen early makes you not just a licensed engineer but a safer one.
Technical competence keeps aircraft flying; human-factors awareness keeps them — and the people who maintain them — safe.