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:

45.Sensory Register: Brief storage of sensory information (visual, auditory, tactile)

46.Working Memory: Active processing of information (limited capacity, approximately 7±2 items)

47.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:

327.Lack of communication – Failure to share information effectively

328.Complacency – Overconfidence from familiarity

329.Lack of knowledge – Insufficient training or experience

330.Distraction – Interruption of attention

331.Lack of teamwork – Poor collaboration

332.Fatigue – Physical or mental exhaustion

333.Lack of resources – Insufficient tools, equipment, or personnel

334.Pressure – Time or organisational pressure

335.Lack of assertiveness – Failure to speak up about concerns

336.Stress – Physical or psychological strain

337.Lack of awareness – Failure to recognise the situation

338.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:

390.Identifying hazards

391.Determining who might be harmed and how

392.Evaluating the risk (likelihood and severity)

393.Implementing control measures

394.Recording and reviewing the assessment

Hierarchy of Control:

396.Elimination: Remove the hazard entirely

397.Substitution: Replace with a less hazardous alternative

398.Engineering controls: Isolate people from the hazard

399.Administrative controls: Change how people work

400.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:

453.Review all written documentation (logbook, task cards, worksheets)

454.Conduct a verbal briefing with the outgoing shift

455.Walk around the aircraft/work area to verify status

456.Confirm understanding of all outstanding items

457.Sign for receipt of handover information

458.Record any discrepancies or concerns

Error Reporting Procedure:

460.Immediately report the error to supervision

461.Complete an occurrence report (confidential where possible)

462.Document the circumstances (what, when, where, how)

463.Participate in the investigation (without blame)

464.Contribute to the development of preventive measures

Fatigue Management Procedure:

466.Self-assessment of fitness for duty

467.Report fatigue to supervision before starting work

468.Request rest or reassignment if fatigued

469.Use strategic napping during breaks (20-30 minutes)

470.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

577.Read scenarios carefully: Many questions present a maintenance scenario. Identify the key human factor involved before selecting an answer.

578.Distinguish between similar concepts: For example, complacency vs. memory lapse vs. distraction. Consider the specific circumstances described.

579.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.

580.Remember the regulatory context: Answers that involve falsifying records, signing without verification, or using unapproved tools are always incorrect.

581.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:

585.Human error is inevitable – the goal is to prevent errors from causing harm

586.Error is influenced by many factors – individual, environmental, organisational, and task-related

587.Communication is critical – effective communication prevents errors and catches them when they occur

588.Fatigue and stress degrade performance – recognising and managing these factors is a professional responsibility

589.Procedures exist for a reason – following approved procedures and documentation is a legal and ethical obligation

590.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.

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