Module 9A: Human Factors (A/B1/B2)

Module 9A: Human Factors (B2)

1. Overview

Module 9A introduces the essential principles of human factors that underpin safe and effective aircraft maintenance. It recognises that the vast majority of aviation accidents and incidents are attributable to human error, not technical failure. This module equips the certifying engineer with the knowledge to understand why errors occur and, more importantly, how to prevent them. The syllabus covers the interaction between individuals, their physical environment, their social and organisational context, and the tasks they perform. For the B2 avionics engineer, this is particularly relevant given the high cognitive demand, complexity of systems, and the criticality of precise, procedure-driven work.

The module is structured around the "Dirty Dozen" – twelve common human error preconditions – and explores the broader topics of human performance and limitations, social psychology, the physical environment, and the factors that shape a positive safety culture. The ultimate goal is to foster a professional mindset where safety is the primary driver of every action, from task planning to certification.

2. Key Concepts Explained in Detail

2.1 Human Performance and Limitations (Syllabus 9.2)

This section addresses the inherent capabilities and limitations of the human body and mind that directly affect maintenance tasks.

• Vision: Visual acuity, the ability to distinguish fine details, is critical for reading part numbers, identifying wire colours, and inspecting components. Factors affecting vision include:
• Lighting: Inadequate or glare-producing lighting (typically below 500 lux for detailed work) forces the eyes to strain, increasing error rates and fatigue.
• Colour Perception: For B2 engineers, the ability to correctly distinguish coloured wires and indicator lights is paramount. Colour vision deficiencies (e.g., red-green colour blindness) must be known and mitigated.
• Accommodation: The eye's ability to focus on near objects diminishes with age (presbyopia), necessitating corrective lenses for detailed work.
• Hearing: Essential for detecting abnormal noises during functional tests (e.g., bearing whine, relay chatter) and for receiving verbal instructions. High ambient noise levels in hangars or on the flight line can mask these cues and impair communication.
• Information Processing: The brain has a limited capacity for conscious, simultaneous processing. This is why multi-tasking is inefficient and error-prone. Our memory is also fallible:
• Short-term (working) memory holds information for seconds and is easily disrupted by interruptions.
• Long-term memory is for stored knowledge but is susceptible to recall errors, especially under stress or fatigue.
• Perception: We interpret the world based on our expectations and past experience. This can lead to "seeing what we expect to see" rather than what is actually there.
• Health and Hygiene: General health, including proper nutrition and hydration, directly impacts cognitive function. Illness, dehydration, and poor sleep quality degrade concentration, reaction time, and decision-making.

2.2 Social Psychology (Syllabus 9.3)

This area examines how we interact with others and how those interactions can influence behaviour.

• Communication: Effective communication is a two-way process. The sender must encode a clear message, and the receiver must actively listen, decode, and confirm understanding. Key principles:
• Clarity: Use unambiguous language, standard terminology, and avoid jargon or slang.
• Feedback: The receiver must confirm what they have heard and understood. For shift handovers, this means asking clarifying questions, not just passively accepting a report.
• Assertiveness: The ability to state one's position or concerns respectfully, even in the face of authority or pressure. A junior technician must be able to challenge a senior engineer if they believe a procedure is unsafe.
• Shift Handover: A formal, structured process for transferring responsibility. It must include the status of the aircraft, incomplete tasks, unresolved faults, and any specific hazards or cautions. The incoming engineer must actively seek clarification to build their own situational awareness.
• Teamwork: Effective teams have clear roles, shared goals, and open communication. A lack of teamwork can lead to tasks being performed in isolation without the benefit of a second check or a different perspective.
• Leadership and Management: The behaviour of supervisors and managers sets the tone for the entire organisation. A manager who prioritises schedule over safety creates a culture where shortcuts are implicitly condoned. Conversely, a manager who values safety and encourages reporting fosters a positive safety culture.
• Peer Pressure: The desire to conform to group norms can be powerful. This can be positive (e.g., a norm of strict adherence to procedures) or negative (e.g., a norm of "getting the job done no matter what").

2.3 Factors Affecting Performance (Syllabus 9.4)

These are the individual and situational conditions that can positively or negatively influence a person's ability to perform a task.

• Fatigue: A state of physical and/or mental exhaustion that reduces alertness, impairs cognitive function, slows reaction time, and degrades decision-making. It is a major contributor to maintenance errors, especially during night shifts, long shifts, or after periods of inadequate rest. Mitigation: Recognise the symptoms (decreased concentration, increased errors, yawning), take planned breaks, and communicate your state to supervision. Continuing to work while fatigued is a violation of safety principles.
• Stress: The body's response to demands placed upon it. Some stress (eustress) can improve performance, but excessive stress (distress) is detrimental. Sources of stress include time pressure, workload, personal problems, and poor working relationships. Mitigation: Manage workload, take breaks, and use structured troubleshooting techniques to avoid becoming overwhelmed by complex problems.
• Complacency: A state of self-satisfaction and overconfidence born from repeated success. It leads to a reduction in vigilance and a failure to recognise risks. The engineer who has performed a task "a hundred times" is at high risk of missing a critical step. Mitigation: Always approach every task as if it were the first time, use checklists, and actively cross-check your work against the approved data.
• Distraction: Anything that diverts attention away from the task at hand. This can be an interruption (e.g., a phone call), a secondary task, or even a thought. The risk is that the engineer forgets where they were in a procedure and misses a step. Mitigation: If interrupted, stop the task, complete the interruption, and then re-verify your position in the procedure from the last completed step before resuming.
• Lack of Assertiveness: The failure to speak up when something is wrong or unclear. This can be due to personality, fear of reprisal, or a perceived power imbalance. Mitigation: Training and a positive safety culture that encourages questioning and empowers all personnel to stop a task if they have concerns.
• Norms: Unwritten rules or habits that develop within a group or organisation and deviate from approved procedures. They are often rationalised as "the way we do things here" or "it works fine." Norms are extremely dangerous because they become accepted practice despite being non-compliant. Mitigation: A strong safety culture that challenges unsafe practices and reinforces that approved procedures are the only acceptable way.
• Hazardous Attitudes: Specific negative mindsets that increase the risk of unsafe behaviour. These include:
• Anti-authority: "Don't tell me what to do."
• Impulsivity: "Do something quickly."
• Invulnerability: "It won't happen to me."
• Macho: "I can do it."
• Resignation: "What's the use?"
• Pressure: The real or perceived need to complete a task quickly. This can come from management, peers, or self-imposed. Pressure can lead to shortcuts, skipped steps, and a focus on speed over safety. Mitigation: The engineer must recognise that safety is non-negotiable and that any pressure to violate procedures must be resisted and reported.
• Lack of Resources: The unavailability of the correct tools, equipment, data, or personnel to perform a task safely. This includes using non-approved tools or working with unstable power supplies. Mitigation: Stop the task and secure the correct resources before proceeding.

2.4 Physical Environment (Syllabus 9.5)

The working environment has a direct impact on human performance.

• Lighting: As discussed, poor lighting is a major cause of errors. The engineer must ensure adequate illumination for the specific task.
• Noise: High noise levels can cause hearing damage, increase stress, and interfere with communication. Hearing protection must be used, and communication methods must be adapted.
• Temperature and Humidity: Extreme temperatures cause discomfort, fatigue, and reduced dexterity. High humidity can cause condensation and electrical hazards.
• Vibration: Prolonged exposure to vibration can cause fatigue and reduce fine motor control.
• Hazardous Materials: Exposure to chemicals (fuels, solvents, sealants) can cause acute or chronic health effects. Material Safety Data Sheets (MSDS) must be consulted, and personal protective equipment (PPE) worn.
• Electromagnetic Radiation: High-power RF emitters, such as weather radar, pose a burn hazard. Metal objects (jewellery, watches) can act as antennas and concentrate RF energy, causing severe burns. The radar must be de-energised or the area cleared before any work is performed in the beam path.

2.5 Tasks (Syllabus 9.6)

The design and nature of the task itself can influence error rates.

• Repetitive Tasks: These lead to boredom and complacency. The engineer's mind may wander, and critical steps can be missed.
• Complex Tasks: These place a high demand on cognitive resources, increasing the potential for overload and errors.
• Physical Tasks: These can cause fatigue and musculoskeletal injuries.
• Task Design: Good task design includes clear, unambiguous instructions, logical sequencing, and appropriate tooling. The use of checklists is a key defence against error, especially for multi-step procedures.

2.6 Communication (Syllabus 9.7)

This is a dedicated topic reinforcing the principles from social psychology. It covers the importance of clear, concise, and confirmed communication in all aspects of maintenance, including:

• Shift handovers.
• Verbal instructions.
• Written documentation (task cards, log books).
• Reporting errors and defects.

2.7 Human Error (Syllabus 9.8)

This section focuses on the nature of error itself.

• Error Models: The "Swiss Cheese Model" (James Reason) illustrates how multiple layers of defence (procedures, training, inspections) can all have holes (latent conditions), and an error can pass through all of them if they align.
• Types of Error:
• Slips and Lapses: Errors of execution where the plan is correct but the action is not performed correctly (e.g., missing a step due to distraction).
• Mistakes: Errors of planning where the action is performed correctly but the plan is wrong (e.g., using the wrong test procedure).
• Violations: Deliberate deviations from approved procedures. These are not errors but conscious choices, often driven by pressure, norms, or hazardous attitudes.

2.8 Hazards in the Workplace (Syllabus 9.9)

This covers the general safety risks in a maintenance environment, including:

• Mechanical hazards (moving aircraft, rotating machinery).
• Electrical hazards (high voltage, static discharge).
• Chemical hazards (fuels, solvents).
• Physical hazards (noise, radiation, working at height).
• The use of PPE and adherence to safety data sheets and local safety regulations.

3. Important Regulations, Procedures, and References

• Regulation (EU) No 1321/2014, Annex III (Part-66): This is the core regulation. Appendix I defines the basic knowledge syllabus, and Module 9A is a mandatory requirement for all B1, B2, and B3 licence categories.
• Acceptable Means of Compliance and Guidance Material (AMC/GM) to Part-66: These documents provide the detailed interpretation of the regulation. They emphasise that human factors training is not just theoretical but must be integrated into the engineer's daily practice and the organisation's safety culture.
• AMC/GM to Part-145: While Part-145 is for maintenance organisations, its AMC/GM heavily references human factors principles. It requires organisations to have procedures for shift handover, error reporting, and fatigue risk management.
• AMC 20-8: This is a general AMC on "Human Factors" that provides a comprehensive framework for understanding and managing human error in aviation maintenance.
• The "Dirty Dozen": A list of 12 common human error preconditions developed by Transport Canada and adopted globally. They are: 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.

4. Common Relationships Between Concepts

The "Dirty Dozen" factors are not isolated; they are deeply interconnected. Understanding these relationships is key to effective error prevention.

• Fatigue → Complacency → Distraction: A fatigued engineer is more likely to become complacent about a task they have done many times, and their reduced attention makes them more susceptible to distraction, leading to a missed step.
• Pressure → Norms → Violations: A manager's pressure to meet a deadline can lead to a team developing a norm of skipping certain checks. This norm, now an accepted practice, is a violation of the approved procedure.
• Poor Communication → Lack of Situational Awareness → Error: An incomplete shift handover leaves the incoming engineer with poor situational awareness. They may then make a wrong decision or perform a task incorrectly because they lack the full picture.
• Lack of Resources → Stress → Poor Decision-Making: When the correct tool or data is unavailable, the engineer experiences stress. This stress can impair their judgment, leading them to make a poor decision, such as using a non-approved substitute.
• Hazardous Attitude (Invulnerability) → Violation: An engineer with an "it won't happen to me" attitude is more likely to take shortcuts or use defective equipment, directly violating safety procedures.

5. Typical Exam Focus Points

For the B2 Module 9A exam, candidates should be prepared to:

• Identify the "Dirty Dozen" factor in a given scenario. The questions will describe a realistic maintenance situation, and you must correctly diagnose the primary human factor at play (e.g., is it complacency or distraction? Is it a norm or a violation?).
• Understand the difference between similar factors. For example, know the distinction between:
• Complacency (overconfidence from familiarity) and Distraction (an interruption that breaks focus).
• Norms (unwritten, accepted group behaviour) and Violations (a deliberate, individual act against a rule).
• Physiological factors (vision, hearing) and Psychological factors (stress, motivation).
• Apply the principles of communication, especially regarding shift handover. The correct action is always to seek clarification and confirm understanding.
• Know the correct action to mitigate a risk. For fatigue, it is to stop and rest/communicate. For poor lighting, it is to stop and correct the lighting. For pressure, it is to follow the approved data and not take shortcuts.
• Recognise the importance of situational awareness and how it can be degraded (e.g., by working alone, using a mirror, or receiving a poor handover).
• Identify hazards in the physical environment, such as RF radiation from radar, and know the correct safety precautions.
• Understand the regulatory framework (Part-66, Part-145, AMC 20-8) and the role of human factors training in maintaining a positive safety culture.