Human Factors FAQ for EASA Part-66 Candidates
Human factors is the science of how people perform in the maintenance environment — and why errors happen despite good intentions. Module 9 (Human Factors) is a basic module required for every EASA Part-66 licence category, covering the Dirty Dozen, fatigue, shift turnover, communication, and error prevention. This FAQ covers the frameworks, the risks, and how Skylicence Europe prepares you for the human factors knowledge every Part-66 engineer is expected to have.
Skylicence Europe Team
EASA Part-66 exam preparation specialists — helping engineers earn their Part-66 licence since 2025
Human Factors in the EASA Part-66 System
Human factors knowledge is woven throughout the EASA Part-66 certification path. Module 9 (Human Factors) is a basic module required for every licence category — 34 questions in 45 minutes with a 75 percent pass mark (66.A.25). The Part-66 Appendix I syllabus and the AMC material supporting the regulation treat human factors as core professional knowledge, and Part-145 maintenance organisations are required to train personnel in error prevention.
The stakes are real. Research consistently shows that human error is a contributing factor in the majority of maintenance-related accidents and incidents. Errors range from minor documentation mistakes to catastrophic failures that have caused loss of life. By building human factors awareness into the licensing requirements for every category, EASA ensures that certified engineers enter the workforce conscious of human performance limitations — and equipped with the tools to manage them. This is not abstract theory; it is life-saving knowledge applied every day in the hangar.
What makes human factors knowledge unique is that it is universal. Every engineer — whether working on light piston aircraft or large transport-category jets — faces the same challenges: fatigue from shift work, communication barriers in the hangar, pressure to complete work on schedule, the temptation to cut corners on routine tasks, and the physical strain of awkward working positions. The skills taught in human factors training — recognising your own limitations, communicating assertively, managing stress, and building a safety culture — transfer across every maintenance environment. Skylicence Europe helps you internalise these skills through scenario-based practice that connects each concept to real maintenance situations.
The Dirty Dozen and Beyond
The Dirty Dozen is the most recognised human factors framework in aviation maintenance, and it occupies a central place in the Module 9 syllabus. It identifies twelve common precursors to human 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. Each factor is a condition that, when present, increases the likelihood of an error. Effective training tests not just whether you can name the twelve factors, but whether you can identify which factor is present in a given scenario and recommend the right countermeasure. For example, if a scenario describes an experienced technician skipping a required inspection step because they have performed the same task hundreds of times without incident, the factor is complacency — and a written checklist is the appropriate countermeasure.
Beyond the Dirty Dozen, the Module 9 syllabus uses complementary models. The SHELL model helps analyse interactions between the individual (Liveware) and the Software (procedures, checklists), Hardware (tools, equipment), and Environment (lighting, noise, temperature) elements of the workplace. The Reason Swiss Cheese Model explains how organisational defences — training, procedures, inspections, supervision — are breached when multiple conditions align. The PEAR model (People, Environment, Actions, Resources) provides a framework for task analysis. Together, these models give you a richer toolkit for analysing and preventing errors than the Dirty Dozen alone.
Frequently Asked Questions
What is human factors in aviation maintenance and why does EASA emphasise it?
Human factors is the study of how human performance — physical, psychological, and organisational — affects maintenance safety and quality. EASA emphasises it because studies consistently show that human error is a contributing factor in the majority of aviation maintenance errors, and roughly 12 to 15 percent of aviation accidents involve maintenance as a cause. EASA addresses this through Module 9 (Human Factors), a basic module required for every Part-66 licence category, and through the human factors training requirements for Part-145 maintenance organisations. Skylicence Europe includes human factors scenarios in its question bank so you internalise the concepts every certifying engineer is expected to know.
What is the Dirty Dozen and why is it important?
The Dirty Dozen is a human factors framework that identifies twelve common error precursors in aviation maintenance: 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. Originally developed in the 1990s by Gordon Dupont, it has been adopted worldwide — including by EASA-aligned training programmes and the ICAO-endorsed guidance used across Europe. You should know all twelve factors, understand what each means in a maintenance context, and be able to identify which factor is at play in a given scenario. For example, a technician who skips a required step because they have done the same task hundreds of times is experiencing complacency. Skylicence Europe includes scenario-based Dirty Dozen questions with realistic hangar situations.
How is fatigue tested in the EASA Part-66 Module 9 exam?
Fatigue is one of the most critical human factors in aviation maintenance, and it has a dedicated subject area in Module 9. The exam covers the causes of fatigue (sleep deprivation, circadian disruption, extended duty, physical exertion), its effects (reduced attention, slower reaction time, missed inspection items, procedural non-compliance), and countermeasures such as strategic napping, rest periods, and shift scheduling that limits overtime. Fatigue awareness also appears in MTO training curricula and in Part-145 organisation training programmes. You should be able to apply fatigue concepts to realistic maintenance scenarios — for example, identifying the fatigue risk in a night-shift engine change.
Why is shift turnover such a common source of maintenance errors?
Shift turnover — the handover of an aircraft and its work packages between shifts — is one of the most vulnerable moments in maintenance. Information can be lost, assumed, or never communicated: a task left incomplete, a component left disconnected, a test not yet run. Human factors research identifies this as a classic breakdown in communication. Best practices include face-to-face turnovers, written handover notes, reviewing the work package and logbook together, confirming aircraft configuration (such as which panels are open or which circuits are de-energised), and never assuming the next shift knows what you know. EASA-aligned training emphasises structured turnover processes. Skylicence Europe scenarios on shift handover test your ability to spot the communication gaps that lead to errors.
What other human factors models should I know?
Beyond the Dirty Dozen, the models most commonly covered in the Module 9 syllabus are the SHELL model (Software, Hardware, Environment, Liveware) for analysing the interfaces between people and their workplace; the Reason Swiss Cheese Model, which explains how organisational defences are breached when multiple failures align; and the PEAR model (People, Environment, Actions, Resources) used for task analysis. The ICAO Human Factors Digests and the UK CAA CAP 716 / CAP 718 publications draw on these frameworks and are standard references for the module. You should be able to apply the appropriate model to a maintenance scenario — for example, identifying a Liveware-Software mismatch when a checklist uses confusing language. Skylicence Europe covers each model with explanation cards and applied practice questions.
Is human factors training required for maintenance organisations?
Yes. Under the Part-145 requirements, approved maintenance organisations must include human factors in their training programmes, and the Module 9 syllabus is a basic requirement for every Part-66 licence category. This typically includes the Dirty Dozen, communication, fatigue awareness, error reporting, and just culture. Many Part-145 operators also run FOD prevention and safety management (SMS) programmes that reinforce human factors concepts daily. If you are working toward your Part-66 licence while employed at a maintenance organisation, you will likely receive this training on the job — and the concepts will appear again in your module exam.
How is human factors evaluated in the practical assessments?
Human factors are evaluated indirectly during your practical experience and assessments under 66.A.30: your supervisor and the assessors observe your communication, your use of technical data, your attention to detail, and your safety practices throughout the practical tasks. Expect questions about error prevention, using the correct manual, verifying your work, and how you would handle pressure or interruptions. An assessor may ask how you would respond if a colleague was about to install a part incorrectly. Demonstrating human factors awareness — speaking up, double-checking, following procedures — is part of earning a recommendation for licence issue. Skylicence Europe scenario questions help you practise these professional behaviours.
What are the most common maintenance error types the exams target?
Maintenance error data and the Module 9 syllabus focus on recurring error categories: incorrect installation (parts installed backwards, wrong torque, missing hardware), improper lubrication, incorrect part, incorrect assembly, foreign object damage (FOD), improper wiring, and missed inspection steps. Each of these traces back to one or more Dirty Dozen factors — typically complacency, distraction, pressure, or lack of knowledge. The EASA approach to error prevention is not punishment but system improvement: reporting culture, redundancy through independent inspection, checklists, and tool control. Understanding how errors happen — and how systems catch them — is core Module 9 knowledge. Skylicence Europe questions connect specific error types to the human factors behind them.
How should I study human factors for the Module 9 exam?
Human factors knowledge is best learned through scenarios, not memorisation. First, learn the key frameworks — the Dirty Dozen, SHELL, Swiss Cheese, PEAR — and what each contributes. Second, study the specific topics: fatigue, communication, teamwork, stress, complacency, pressure, and safety culture. Third, practise applying them to realistic maintenance situations: identify the factor at play, then choose the best corrective action. Use the Module 9 syllabus references — the ICAO Human Factors Digests, CAP 716 / CAP 718, and the AMC material supporting Part-66. Skylicence Europe supports this applied approach with scenario-based questions and explanations that walk through the reasoning step by step.
Can human factors knowledge really help my daily work as an engineer?
Absolutely — human factors knowledge is directly applicable to daily maintenance work, arguably more than any other subject. Understanding the Dirty Dozen helps you recognise when you or your teammates are at risk of error due to fatigue, complacency, or pressure. Knowing how to communicate assertively helps you speak up when you spot a potential safety issue. Understanding ergonomics helps you set up your workspace to reduce injury and error potential. Recognising stress and fatigue in yourself and others helps you decide when to continue work and when to stop. EASA requires human factors knowledge because it prevents maintenance errors before they happen. Skylicence Europe reinforces this practical connection by explaining how each concept applies to real hangar scenarios.
Do B2 avionics candidates need human factors too?
Yes. Module 9 is a basic module required for every Part-66 licence category — A, B1.1-B1.4, B2 and B3 — with the same 34-question, 45-minute exam and the same 75 percent pass mark. Avionics engineers face the same human factors risks as mechanical engineers: fatigue from shift work, communication barriers, pressure, and complacency. The scenarios in the module exams are sometimes framed around avionics tasks — wiring errors, incorrect software loading, or component interchange mistakes — but the underlying factors and countermeasures are identical. Skylicence Europe includes avionics-framed human factors scenarios alongside mechanical ones.
How does Skylicence Europe help me master human factors?
Skylicence Europe includes a dedicated Module 9 (Human Factors) question bank covering the Dirty Dozen, SHELL, Swiss Cheese, PEAR, fatigue, shift turnover, communication, and error prevention — with the 34-question, 45-minute format replicated in timed mock exams. Features include AI-powered adaptive difficulty, detailed explanations referencing the Module 9 syllabus and its recommended references, and scenario-based questions that mirror how human factors knowledge is applied in maintenance practice. Performance analytics show your accuracy across each human factors topic so you can focus your review. One licence category is free at Skylicence Europe — start practising today.
For a deeper look at human factors concepts, check out our Aviation Human Factors for EASA Part-66 guide and the study techniques guide. Visit the main Skylicence Europe FAQ for platform-related questions.
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