Module 9A: Human Factors (A/B1/B2) – EASA Part-66 Study Material

1. Module Overview

Module 9A addresses the critical relationship between human performance and aviation maintenance safety. It is a mandatory module for all B1, B2, and B3 licence categories, reflecting the industry's recognition that human error is a primary contributing factor in aviation incidents and accidents. The module is designed to provide certifying staff with the knowledge and awareness necessary to recognise, manage, and mitigate the effects of human factors in their daily work.

The syllabus is divided into ten sub-modules, each addressing a specific aspect of human factors:

9.1 General – The need to take human factors into account
9.2 Human Performance and Limitations – Vision, hearing, information processing, memory, and attention
9.3 Social Psychology – Communication, teamwork, leadership, and organisational culture
9.4 Factors Affecting Performance – Physical environment, stress, fatigue, and time pressure
9.5 Physical Environment – Noise, lighting, temperature, and vibration
9.6 Tasks – Physical work, repetitive tasks, and inspection requirements
9.7 Communication – Verbal, written, and non-verbal communication; shift handover
9.8 Human Error – Error models, error types, and error prevention
9.9 Hazards in the Workplace – Risk assessment and safety management
9.10 Managing Human Factors in Maintenance – Organisational factors and safety culture

The knowledge levels for this module are typically Level 2 (general knowledge) for most sub-modules, with some areas requiring Level 3 (detailed theory) understanding.

2. Key Concepts Explained in Detail

2.1 The Need for Human Factors Awareness (9.1)

Aviation maintenance is a complex, safety-critical activity where the consequences of error can be catastrophic. Historical accident data demonstrates that approximately 80% of aviation accidents involve human error at some level. In maintenance specifically, studies have shown that human factors issues contribute to between 12% and 20% of all aviation accidents and incidents.

The evolution of human factors in aviation began with the recognition that purely technical solutions were insufficient to prevent accidents. The shift from a "blame culture" to a "just culture" represents a fundamental change in how the industry approaches error. Rather than punishing individuals for mistakes, modern safety management systems seek to understand the underlying conditions that allowed the error to occur.

Key regulatory references:

Regulation (EU) No 1321/2014, Annex III (Part-66) – establishes the licensing requirements
Regulation (EU) No 1321/2014, Annex II (Part-145) – requires approved maintenance organisations to have human factors programmes
AMC/GM to Part-145 – provides detailed guidance on human factors training and error management

2.2 Human Performance and Limitations (9.2)

Vision

The human visual system is the primary sensory channel used in maintenance tasks. Understanding its limitations is essential for effective inspection and task performance.

Visual Acuity: The ability to resolve fine detail is measured in terms of the minimum angle of resolution. A person with 20/20 vision can resolve details subtending an angle of 1 arc-minute. Visual acuity decreases with:

Age (presbyopia – loss of near focusing ability)
Fatigue
Poor lighting
Certain medications and medical conditions

Contrast Sensitivity: The ability to distinguish an object from its background. This is particularly important when inspecting for cracks, corrosion, or other defects on surfaces of similar colour. Contrast sensitivity declines with age and under poor lighting conditions.

Colour Vision: Approximately 8% of males have some form of colour vision deficiency. This can affect tasks such as identifying coloured wiring, reading indicator lights, or interpreting colour-coded documentation.

Peripheral Vision: The ability to detect objects outside the central field of view. Peripheral vision is more sensitive to movement but has poor detail resolution.

Depth Perception: The ability to judge distances and spatial relationships. This is critical for tasks such as inserting pins, aligning components, or using tools in confined spaces.

Hearing

Hearing is essential for detecting abnormal noises during engine runs, recognising warning signals, and effective communication. Age-related hearing loss (presbycusis) typically affects high frequencies first. Prolonged exposure to noise above 85 dB(A) can cause permanent hearing damage.

Key hearing considerations:

The ear requires approximately 16 hours to recover from a single day's exposure to high noise levels
Hearing protection must be worn when noise levels exceed 85 dB(A)
Communication in noisy environments requires specific techniques (e.g., headsets, hand signals, or written communication)

Information Processing

The human brain processes information through a series of stages:

Sensory Register: Brief storage of sensory information (visual, auditory, tactile)
Working Memory: Active processing of information (limited capacity, approximately 7±2 items)
Long-Term Memory: Permanent storage of knowledge and skills

Attention: The ability to focus on relevant information while ignoring distractions. Attention is a limited resource that can be:

Selective: Focusing on one source of information while ignoring others
Divided: Splitting attention between multiple tasks (leads to degraded performance)
Sustained: Maintaining attention over extended periods (declines after 20-30 minutes)

Vigilance: The ability to maintain attention on a task over time. Vigilance declines significantly after 30 minutes of continuous monitoring, particularly in tasks with low event rates (e.g., visual inspection).

Memory

Memory is not a perfect recording system; it is reconstructive and subject to error.

Short-term (Working) Memory:

Limited capacity (approximately 7±2 chunks of information)
Information decays within 15-30 seconds unless rehearsed
Susceptible to interference from competing information
Degraded by stress, fatigue, and distraction

Long-term Memory:

Effectively unlimited capacity
Information is stored semantically (by meaning)
Retrieval is influenced by context and emotional state
Subject to distortion over time

Memory Errors in Maintenance:

Prospective memory failures: Forgetting to perform an intended action (e.g., forgetting to record a torque value)
Retrospective memory failures: Forgetting information that was previously learned
Source monitoring errors: Confusing whether an action was actually performed or only planned

Mitigation strategies:

Use of checklists and documentation
Written handover records
"Touch and confirm" techniques
Structured task cards with sign-off requirements

2.3 Social Psychology (9.3)

Social psychology examines how individuals interact with others and how these interactions affect performance and safety.

Communication

Effective communication is fundamental to safe maintenance. Communication failures are implicated in a significant proportion of maintenance errors.

Communication Channels:

Verbal: Face-to-face, telephone, radio – subject to misunderstanding, accent, and language barriers
Written: Logbooks, task cards, technical documentation – subject to illegibility and ambiguity
Non-verbal: Body language, facial expressions, gestures – can contradict verbal messages

Barriers to Effective Communication:

Language differences (particularly in international operations)
Technical jargon and abbreviations
Assumptions about shared understanding
Hierarchical barriers (junior staff reluctant to question senior staff)
Time pressure and workload
Environmental noise

Communication Techniques:

Closed-loop communication: The receiver repeats back the message to confirm understanding
Challenge and response: One person reads the procedure aloud while another performs the steps
Read-back/hear-back: Used in radio communication to verify message accuracy
Structured handover: Using standardised formats for shift changes

Teamwork and Leadership

Maintenance is increasingly a team activity. Effective teamwork requires:

Clear roles and responsibilities
Open communication channels
Mutual respect and trust
Willingness to raise concerns
Effective leadership that encourages input from all team members

The "Just Culture" Concept:

A just culture recognises that errors will occur but distinguishes between:

Honest errors: Mistakes made despite best intentions – should be reported and learned from
At-risk behaviour: Actions that increase risk without malicious intent – should be addressed through training and awareness
Reckless behaviour: Deliberate disregard for safety – should be subject to disciplinary action

2.4 Factors Affecting Performance (9.4)

Stress

Stress is the body's response to demands placed upon it. Some stress (eustress) can enhance performance, but excessive stress (distress) degrades it.

Sources of Stress in Maintenance:

Time pressure and deadlines
Workload (both overload and underload)
Organisational factors (management style, job security)
Personal factors (family, health, finances)
Environmental factors (noise, temperature, lighting)

Effects of Stress on Performance:

Reduced attention and concentration
Impaired decision-making
Tunnel vision (focusing on one aspect while ignoring others)
Increased error rate
Reduced communication effectiveness
Physical symptoms (headaches, muscle tension, fatigue)

The Yerkes-Dodson Law:

Performance improves with increasing arousal up to an optimal level, after which further increases in arousal degrade performance. The optimal level varies with task complexity – simple tasks require higher arousal, complex tasks require lower arousal.

Fatigue

Fatigue is a state of reduced physical and mental capability resulting from inadequate rest, prolonged wakefulness, or sustained cognitive or physical effort.

Types of Fatigue:

Acute fatigue: Short-term, resulting from a single period of activity or sleep deprivation
Chronic fatigue: Long-term, resulting from cumulative sleep debt or persistent overwork
Physical fatigue: Muscular exhaustion from sustained physical activity
Mental fatigue: Cognitive exhaustion from sustained mental activity

Effects of Fatigue:

Reduced vigilance and attention
Impaired memory and decision-making
Slower reaction times
Reduced manual dexterity
Increased error rates
Reduced motivation and mood
Impaired communication

Circadian Rhythms:

The human body operates on approximately 24-hour cycles that regulate sleep-wake patterns, body temperature, and hormone secretion. The body's natural "low point" occurs between approximately 03:00 and 05:00, when alertness and performance are at their lowest. Night shifts disrupt circadian rhythms, leading to:

Reduced alertness during work hours
Poor quality daytime sleep
Cumulative sleep debt
Increased error risk

Fatigue Management Strategies:

Recognition of personal limitations
Reporting fatigue to supervision
Strategic napping (20-30 minutes) during breaks
Proper sleep hygiene (dark, quiet, cool sleeping environment)
Limiting consecutive night shifts
Adequate rest between shifts

Time Pressure

Time pressure is a significant stressor in line maintenance, where aircraft must be returned to service to meet schedules.

Effects of Time Pressure:

Increased error rates
Skipping or rushing steps
Reduced checking and verification
Poor communication
Increased risk-taking behaviour

Managing Time Pressure:

Prioritising safety over schedule
Communicating concerns about unrealistic deadlines
Using checklists to ensure completeness
Seeking assistance when workload is excessive
Recognising that the cost of an error far exceeds the cost of a delay

2.5 Physical Environment (9.5)

The physical environment significantly affects human performance. Understanding and managing environmental factors is essential for safe maintenance.

Lighting

Adequate lighting is critical for visual inspection and precision tasks.

Lighting Requirements:

General work areas: 200-500 lux
Detailed inspection tasks: 500-1000 lux
Precision work (e.g., instrument calibration): 1000-2000 lux
Emergency lighting: minimum 50 lux

Effects of Poor Lighting:

Reduced visual acuity
Increased eye strain and fatigue
Missed defects during inspection
Misreading instruments and documentation
Increased error rates

Lighting Considerations:

Uniformity of illumination (avoid shadows and glare)
Colour rendering (ability to distinguish colours accurately)
Flicker (can cause eye strain and headaches)
Positioning of light sources (avoid direct glare into eyes)

Noise

Noise is unwanted sound that can interfere with communication and cause physiological and psychological effects.

Noise Levels:

Normal conversation: 60 dB(A)
Busy workshop: 80-90 dB(A)
Jet engine run-up: 120-140 dB(A)
Hearing damage threshold: 85 dB(A) over 8 hours

Effects of Noise:

Hearing damage (permanent or temporary)
Interference with communication
Increased stress and irritability
Reduced concentration
Masking of warning signals

Noise Management:

Hearing protection (earplugs, earmuffs) when noise exceeds 85 dB(A)
Engineering controls (acoustic enclosures, sound barriers)
Administrative controls (limiting exposure time)
Communication systems (headsets, signal lights)

Temperature and Humidity

Extreme temperatures affect both physical and cognitive performance.

Cold Environments:

Reduced manual dexterity (particularly below 15°C)
Reduced tactile sensitivity
Impaired cognitive function
Increased error rates
Risk of hypothermia in extreme conditions

Hot Environments:

Fatigue and lethargy
Reduced concentration
Increased error rates
Risk of heat exhaustion and heat stroke
Sweating can affect grip and tool handling

Comfort Range:

Physical work: 15-25°C
Precision work: 20-25°C
Humidity: 40-60% relative humidity

Vibration

Prolonged exposure to vibration can cause:

Reduced manual dexterity
Hand-arm vibration syndrome (white finger)
Fatigue and discomfort
Reduced sensory feedback

2.6 Tasks (9.6)

Task design significantly influences human performance and error rates.

Physical Work

Maintenance tasks often involve:

Lifting and carrying heavy components
Working in awkward positions
Reaching and stretching
Working in confined spaces
Repetitive movements

Ergonomic Considerations:

Task design should minimise physical strain
Proper lifting techniques should be used
Adequate access and working space should be provided
Tools should be appropriate for the task
Regular breaks should be taken during physically demanding work

Repetitive Tasks

Repetitive tasks lead to:

Boredom and reduced vigilance
Loss of concentration
Increased error rates
Physical fatigue and discomfort

Managing Repetitive Tasks:

Task rotation to vary activities
Regular breaks
Self-checking techniques
Awareness of the increased risk of complacency

Inspection Tasks

Inspection is a critical maintenance activity that is particularly susceptible to human error.

Factors Affecting Inspection Performance:

Visual acuity and lighting
Time pressure
Task complexity
Experience and training
Fatigue and stress
Expectations (seeing what you expect to see)

Inspection Techniques:

Systematic scanning patterns
Use of appropriate magnification aids
Adequate lighting
"Fresh eyes" inspections (second inspector)
Structured inspection procedures

2.7 Communication (9.7)

Communication is the exchange of information between individuals. In maintenance, effective communication is essential for safety.

Shift Handover

The shift handover is a critical communication point where information is transferred between outgoing and incoming shifts.

Information to be Transferred:

Status of ongoing tasks
Completed and incomplete work
Snags and discrepancies
Tooling and equipment status
Aircraft configuration
Any safety concerns

Handover Requirements:

Written documentation (logbook entries, task cards)
Verbal briefing (face-to-face)
Walk-around inspection (where appropriate)
Confirmation of understanding

Risks of Inadequate Handover:

Loss of critical information
Duplication or omission of work
Incorrect aircraft configuration
Latent errors (errors that remain undetected until later)

Written Communication

Maintenance documentation must be:

Legible (readable handwriting or printed)
Accurate (correct information)
Complete (all required entries made)
Timely (completed at the time of the task)
Signed and dated by the responsible person

Common Documentation Errors:

Illegible handwriting
Incomplete entries
Incorrect data (wrong part numbers, serial numbers)
Signing without performing the work
Using unauthorised abbreviations

2.8 Human Error (9.8)

Human error is the failure to perform a task within specified limits. Understanding error mechanisms is essential for error prevention.

Error Models

The Shell Model:

The Shell model (Software, Hardware, Environment, Liveware) is a conceptual framework for analysing human factors in aviation.

Software (S): Procedures, documentation, checklists, computer programs
Hardware (H): Tools, equipment, aircraft systems, physical components
Environment (E): Physical environment, organisational culture, regulatory framework
Liveware (L): The human element – individuals and teams

The model focuses on the interfaces between these components:

Liveware-Software: The interaction between humans and procedures/documentation
Liveware-Hardware: The interaction between humans and tools/equipment
Liveware-Environment: The interaction between humans and the working environment
Liveware-Liveware: The interaction between individuals and teams

Mismatches at these interfaces are the root causes of human error.

The Reason Model (Swiss Cheese Model):

James Reason's model describes how accidents occur when multiple layers of defence are breached.

Active failures: Errors committed by frontline personnel (e.g., a technician making a mistake)
Latent conditions: Underlying organisational factors that create the conditions for error (e.g., poor procedures, inadequate training, time pressure)
Defences: Barriers that prevent errors from causing harm (e.g., inspections, checklists, testing)

An accident occurs when the "holes" in the defences align, allowing the error to pass through all layers.

The Dirty Dozen:

The Dirty Dozen is a list of twelve common human error precursors identified by Gordon Dupont:

Lack of communication – Failure to share information effectively
Complacency – Overconfidence from familiarity
Lack of knowledge – Insufficient training or experience
Distraction – Interruption of attention
Lack of teamwork – Poor collaboration
Fatigue – Physical or mental exhaustion
Lack of resources – Insufficient tools, equipment, or personnel
Pressure – Time or organisational pressure
Lack of assertiveness – Failure to speak up about concerns
Stress – Physical or psychological strain
Lack of awareness – Failure to recognise the situation
Norms – Unwritten rules that deviate from procedures

Error Types

Skill-based Errors:

Occur during routine, well-learned tasks
Result from attention failures or memory lapses
Examples: forgetting a step, omitting a check, using the wrong tool

Rule-based Errors:

Occur when applying rules or procedures
Result from misapplication of a good rule or application of a bad rule
Examples: using an outdated procedure, applying the wrong checklist

Knowledge-based Errors:

Occur in novel situations requiring problem-solving
Result from incomplete knowledge or incorrect mental models
Examples: misdiagnosing a fault, making an incorrect decision

Error Prevention

Individual Strategies:

Use of checklists and documentation
Self-checking techniques (e.g., "touch and confirm")
Taking breaks to maintain vigilance
Reporting errors and near-misses
Seeking clarification when uncertain

Organisational Strategies:

Effective procedures and documentation
Adequate training and competency assessment
Appropriate staffing levels
Safety management systems
Just culture (encouraging error reporting)
Continuous improvement based on error analysis

2.9 Hazards in the Workplace (9.9)

Workplace hazards in maintenance environments include:

Physical Hazards:

Moving aircraft and vehicles
Rotating machinery
Electrical hazards
Pressurised systems
Lifting operations
Confined spaces
Working at height
Hazardous materials (fuels, chemicals, composites)

Chemical Hazards:

Fuels and solvents
Lubricants and hydraulic fluids
Cleaning agents
Composite materials (carbon fibre, resins)
Battery acids and electrolytes

Biological Hazards:

Mould and bacteria in aircraft systems
Contaminated fuel or water systems

Risk Assessment:

The process of identifying hazards and evaluating the risk they present. Risk is a function of the likelihood of an event and the severity of its consequences.

Risk = Likelihood × Severity

Risk assessment involves:

Identifying hazards
Determining who might be harmed and how
Evaluating the risk (likelihood and severity)
Implementing control measures
Recording and reviewing the assessment

Hierarchy of Control:

Elimination: Remove the hazard entirely
Substitution: Replace with a less hazardous alternative
Engineering controls: Isolate people from the hazard
Administrative controls: Change how people work
Personal protective equipment: Protect the individual

2.10 Managing Human Factors in Maintenance (9.10)

Organisational factors significantly influence individual performance and error rates.

Organisational Culture

Safety Culture: The shared values, beliefs, and attitudes that determine how safety is prioritised within an organisation. A positive safety culture is characterised by:

Leadership commitment to safety
Open communication about errors and hazards
Learning from incidents and near-misses
Fair and just treatment of individuals
Continuous improvement

Reporting Culture: An environment where individuals feel able to report errors and hazards without fear of punishment. This requires:

Confidential reporting systems
Non-punitive response to honest errors
Feedback on reported issues
Visible action on reported concerns

Safety Management Systems (SMS)

A Safety Management System is a systematic approach to managing safety, including:

Safety policy and objectives
Safety risk management (hazard identification and risk assessment)
Safety assurance (monitoring and measurement)
Safety promotion (training and communication)

Regulatory Requirements

Part-145 Requirements:

Maintenance organisations must have a human factors programme
Human factors training must be provided to all personnel
Error management systems must be in place
Occurrence reporting systems must be established

Part-66 Requirements:

Certifying staff must demonstrate knowledge of human factors
Human factors training is a mandatory module in the licence syllabus
Continued competency requires periodic human factors refresher training

3. Important Formulas, Regulations, and Procedures

Key Regulatory References

Regulation	Content
Regulation (EU) No 1321/2014, Annex II (Part-145)	Maintenance organisation requirements, including human factors programmes
Regulation (EU) No 1321/2014, Annex III (Part-66)	Licensing requirements, including Module 9A syllabus
Regulation (EU) No 1321/2014, Annex IV (Part-147)	Training organisation requirements
AMC/GM to Part-145	Acceptable means of compliance and guidance material
AMC/GM to Part-66	Guidance on licence requirements and human factors training
ICAO Annex 19	Safety Management Systems
ICAO Doc 9859	Safety Management Manual

Key Formulas

Risk Assessment:

\[ \text{Risk} = \text{Likelihood} \times \text{Severity} \]

Noise Exposure (Daily Dose):

\[ D = \frac{C_1}{T_1} + \frac{C_2}{T_2} + ... + \frac{C_n}{T_n} \]

Where:

\( C \) = Actual exposure time at a given noise level
\( T \) = Permitted exposure time at that noise level

Permitted Exposure Time (for 85 dB(A) criterion with 3 dB exchange rate):

\[ T = \frac{8}{2^{(L - 85)/3}} \]

Where:

\( T \) = Permitted exposure time (hours)
\( L \) = Noise level (dB(A))

Visual Acuity:

\[ \text{Visual Acuity} = \frac{\text{Test Distance}}{\text{Reference Distance}} \]

Standard acuity is 1.0 (20/20 vision)

Key Procedures

Shift Handover Procedure:

Review all written documentation (logbook, task cards, worksheets)
Conduct a verbal briefing with the outgoing shift
Walk around the aircraft/work area to verify status
Confirm understanding of all outstanding items
Sign for receipt of handover information
Record any discrepancies or concerns

Error Reporting Procedure:

Immediately report the error to supervision
Complete an occurrence report (confidential where possible)
Document the circumstances (what, when, where, how)
Participate in the investigation (without blame)
Contribute to the development of preventive measures

Fatigue Management Procedure:

Self-assessment of fitness for duty
Report fatigue to supervision before starting work
Request rest or reassignment if fatigued
Use strategic napping during breaks (20-30 minutes)
Maintain proper sleep hygiene between shifts

4. Common Relationships Between Concepts

The Relationship Between Complacency and Error

Complacency arises from over-familiarity with a task. When a technician has performed a task many times, they may:

Skip steps (particularly checklist use)
Reduce vigilance and attention
Fail to verify their work
Ignore discrepancies

Complacency is most dangerous in experienced personnel who have a high level of skill but reduced attention. The relationship between experience and error is not linear – error rates can increase with experience if complacency develops.

Mitigation: Regular task rotation, self-checking techniques, and a personal commitment to following procedures regardless of familiarity.

The Relationship Between Fatigue and Performance

Fatigue degrades performance across multiple dimensions:

Cognitive: Reduced attention, memory, decision-making
Physical: Reduced dexterity, strength, coordination
Psychological: Reduced motivation, mood, communication

The relationship is cumulative – fatigue builds over consecutive shifts, particularly night shifts. The body's circadian rhythm creates predictable periods of reduced performance (approximately 03:00-05:00 and 15:00-17:00).

Mitigation: Recognition of fatigue as a safety risk, reporting fatigue, and appropriate shift scheduling.

The Relationship Between Communication and Error

Communication failures are implicated in a significant proportion of maintenance errors. The relationship is:

Incomplete information transfer → misunderstanding → error
Verbal-only communication → memory decay → error
Ambiguous language → misinterpretation → error

Mitigation: Written documentation, closed-loop communication, structured handover procedures, and challenge-and-response techniques.

The Relationship Between Environment and Performance

The physical environment directly affects human performance:

Poor lighting → reduced visual acuity → missed defects
Noise → communication interference → misunderstanding
Temperature extremes → reduced dexterity/concentration → errors
Vibration → physical discomfort → reduced precision

Mitigation: Environmental assessment before starting work, use of appropriate lighting and hearing protection, and recognition of environmental limitations.

The Relationship Between Stress and Performance

The Yerkes-Dodson Law describes an inverted-U relationship between arousal (stress) and performance:

Low stress → low arousal → reduced performance (boredom, inattention)
Optimal stress → peak performance (alert, focused)
High stress → high arousal → reduced performance (tunnel vision, errors)

The optimal stress level varies with task complexity:

Simple tasks: Higher optimal arousal
Complex tasks: Lower optimal arousal

Mitigation: Workload management, realistic deadlines, and recognition of personal stress limits.

5. Typical Exam Focus Points

Knowledge Level Expectations

For Module 9A, the typical knowledge levels are:

Level 1 (Overview): General awareness of the need for human factors
Level 2 (General Knowledge): Understanding of key concepts and their application
Level 3 (Detailed Theory): In-depth understanding of error models and prevention strategies

Common Exam Topics

1. The Dirty Dozen

Identify the twelve error precursors
Recognise scenarios that illustrate each precursor
Understand mitigation strategies for each

Exam focus: Scenario-based questions where you must identify which human factor is most directly involved.

2. Error Models

The Shell model (Software, Hardware, Environment, Liveware)
The Reason/Swiss Cheese model (active failures, latent conditions, defences)
The relationship between models and accident causation

Exam focus: Understanding the purpose and application of each model, not just memorising the components.

3. Communication

Shift handover requirements
Barriers to effective communication
Techniques for improving communication (closed-loop, challenge-and-response)
The risks of verbal-only communication

Exam focus: Scenario-based questions about handover situations and appropriate actions.

4. Fatigue

Effects of fatigue on performance
Circadian rhythm effects
Shift work considerations
Fatigue management strategies

Exam focus: Recognising fatigue in scenarios and identifying appropriate actions.

5. Physical Environment

Lighting requirements for different tasks
Noise exposure limits and hearing protection
Temperature effects on performance
Environmental factors in inspection tasks

Exam focus: Identifying the most appropriate action when environmental conditions are inadequate.

6. Complacency

Definition and causes
Relationship to experience and familiarity
Consequences (skipping steps, ignoring limits)
Prevention strategies

Exam focus: Recognising complacency in experienced technicians and understanding its risks.

7. Memory and Attention

Working memory limitations
Effects of interruptions and distractions
Memory lapse scenarios
Mitigation through checklists and documentation

Exam focus: Distinguishing between memory lapses and other error types.

8. Human Error

Error types (skill-based, rule-based, knowledge-based)
Active failures vs. latent conditions
Error prevention strategies
The "sign-off without doing" error

Exam focus: Understanding the mechanisms of error and appropriate responses.

9. Workplace Hazards

Risk assessment principles
Hierarchy of control
Common maintenance hazards
Reporting procedures

Exam focus: Identifying hazards and appropriate control measures.

10. Organisational Factors

Safety culture and just culture
Reporting systems
Management commitment
Regulatory requirements (Part-145, Part-66)

Exam focus: Understanding the role of organisational factors in error prevention.

Exam Strategy

Read scenarios carefully: Many questions present a maintenance scenario. Identify the key human factor involved before selecting an answer.
Distinguish between similar concepts: For example, complacency vs. memory lapse vs. distraction. Consider the specific circumstances described.
Apply the "most appropriate action" principle: Questions often ask what the technician should do. The correct answer is typically the action that prioritises safety, follows procedures, and maintains documentation integrity.
Remember the regulatory context: Answers that involve falsifying records, signing without verification, or using unapproved tools are always incorrect.
Consider the human factors model: When in doubt, apply the Dirty Dozen or Shell model to analyse the situation.

Summary

Module 9A provides certifying staff with the knowledge and awareness to recognise and manage human factors in aviation maintenance. The key principles are:

Human error is inevitable – the goal is to prevent errors from causing harm
Error is influenced by many factors – individual, environmental, organisational, and task-related
Communication is critical – effective communication prevents errors and catches them when they occur
Fatigue and stress degrade performance – recognising and managing these factors is a professional responsibility
Procedures exist for a reason – following approved procedures and documentation is a legal and ethical obligation
Reporting and learning – a just culture that encourages error reporting leads to continuous improvement

The professional certifying staff member integrates these principles into daily practice, maintaining a questioning attitude, using checklists and documentation diligently, and prioritising safety over schedule or convenience.