Human Factors and 'Dirty Dozen' — why people make mistakes in maintenance
The twelve factors behind most human errors — and what Just Culture does about them
Planes rarely break down because metal fails without warning. Far most maintenance-related incidents can be traced back to human factors — a misread manual a forgotten bolt a misunderstanding between two shifts. Therefore 'human factors' takes up as much space in your education as mechanics and electronics and it is a mandatory element in the approved basic training.
§The 12 factors — Dirty Dozen
In 1993 Gordon Dupont while working for Transport Canada developed a list of the twelve most common human factors behind errors in aircraft maintenance. The list — called 'Dirty Dozen' — has since become a permanent part of human factors teaching in the entire industry including in the European Part-145 regulation.
| Factor. | What it means in practice |
|---|---|
| Missing communication | Important information is lost between shift changes or colleagues |
| Complacency | You expect everything to be as it was last time, and check less thoroughly |
| Missing knowledge | You perform a task without fully understanding the procedure behind it. |
| Distraction | An interruption in the middle of a task causes you to skip a step... |
| Missing teamwork | Tasks requiring collaboration are solved separately without coordination |
| Fatigue | Reduced attention and judgment after long shifts or night work |
| Missing resources | Incorrect tool, time or documentation forces you to improvise |
| Press | Time pressure or expectations make you compromise on safety |
| Missing self-assertion | You don't dare speak up even though something seems wrong. |
| Stress | Personal or work-related stress impairs concentration |
| Missing attention | You lose sight of the consequences of an action. |
| Standards | 'That's how we usually do it' replaces the written procedure |
§Just Culture – a culture without scapegoating
The purpose of knowing the twelve factors is not to point fingers but to understand why even experienced and skilled technicians can make mistakes under the wrong circumstances. European safety culture is based on the Just Culture principle: errors must be reported and investigated openly so the organisation can learn from them without the individual automatically being punished — unless there is gross negligence or deliberate violation.
§What it means for you as a student
- 01PLACEHOLDER_41
- 02Speak up if something seems wrong, even towards a more experienced colleague
- 03Report near-misses, even when nothing went wrong — that is how patterns are detected
- 04Use breaks and shift handovers actively; this is where information is typically lost
§From theory to habit
Human factors teaching can easily be perceived as 'soft' theory in a training otherwise filled with mechanics, moments, and electronics. But in practice it is the part of the trade that most often determines whether an otherwise technically correct action ends with a good or bad result. Two students can know exactly the same procedure, but only one avoids the mistake because they have learned to recognize their own tiredness, their own time pressure, or their own tendency to rely too much on memory rather than documentation. That kind of self-awareness is what the training tries to give you, long before you yourself have full responsibility as a certifying employee.
Many workshops also build their daily routines directly around the twelve factors — for example by requiring double-checks from another person on critical tasks by regular breaks during long tasks to counteract fatigue or by written checklists that explicitly must be ticked off instead of being performed 'from memory'. The earlier you get used to such structures as an apprentice the more natural they become later in your career.