General
The need to take human factors into account; incidents attributable to human factors; Murphy's Law.
General, summary notes
- Human factors is the study of how people interact with the tasks, equipment and environment around them, in maintenance, the goal is to design procedures and workplaces that make the correct action the easy action.
- Around 80% of aviation maintenance-related occurrences trace back to human performance, not a mechanical root cause, this is why EASA Part-145 organisations must run a human factors programme.
- "Murphy's Law", if a component can be fitted incorrectly, sooner or later it will be, is the working assumption behind poka-yoke design: asymmetric connectors, keyed fittings and torque-striping exist because relying on care alone eventually fails.
- Human factors does not mean assigning blame to an individual; it means understanding the conditions (the "error trap") that made the error likely, so the same trap does not catch the next technician.
- ⚠ Exam trap: the SHEL(L) model puts Liveware (the person) at the centre, interfacing with Software, Hardware, Environment and other Liveware, most error occurs at a poor-fitting interface, not from one bad decision.
Two experienced technicians independently cross-connect the same pair of hydraulic lines on the same aircraft type over six months. What does this repetition suggest?
A repeated error by different, competent people points to a systemic error trap (e.g. two identical connectors with no keying) rather than two unrelated individual mistakes, the fix is to redesign the interface (mismatched fittings, colour coding), not to retrain the individuals.
SHELL model
SHELL Model
General quiz
General, quiz
1. What proportion of aviation maintenance occurrences are generally attributed to human factors rather than a purely mechanical cause?
Around 80%Around 20%Around 5%2. "Murphy's Law" as applied to maintenance design means:
If a part can be fitted incorrectly, eventually it will beOnly careless technicians make errorsErrors are always the fault of the last person to touch the aircraft3. The primary purpose of a human factors programme in an EASA Part-145 organisation is to:
Reduce the conditions that make error likelyIdentify individuals to discipline after an errorReplace technical training entirely4. The same wiring error is made independently by three different qualified technicians over a year. This most strongly suggests:
A systemic error trap in the design or procedureThree unrelated instances of carelessnessThe technicians need no further consideration5. "Poka-yoke" design features such as keyed connectors exist to:
Make the incorrect action physically difficult or impossibleSpeed up the task regardless of correctnessReplace the need for inspection6. Human factors as a discipline is primarily concerned with:
How people interact with tasks, equipment and each otherThe chemical composition of aircraft materialsEngine thermodynamics7. The SHEL(L) model describes the interfaces between the human and:
Software, hardware, environment and other people (liveware)Speed, height, endurance and liftOnly the aircraft structure8. In the SHEL model, a checklist or work card is part of the:
SoftwareHardwareEnvironment