B-09 Human Factors PDF - CASA Part 66 Training Materials

MODULE 09 Category B1 and B2 Licences CASA B-09 Human Factors  Copyright © 2020 Aviation Australia All rights reserved. No part of this document may be reproduced, transferred, sold or otherwise disposed of, without the written permis...

MODULE 09 Category B1 and B2 Licences CASA B-09 Human Factors  Copyright © 2020 Aviation Australia All rights reserved. No part of this document may be reproduced, transferred, sold or otherwise disposed of, without the written permission of Aviation Australia. CONTROLLED DOCUMENT 2023-01-12 B-09 Human Factors Page 2 of 340 CASA Part 66 - Training Materials Only  Knowledge Levels Category A, B1, B2 and C Aircraft Maintenance Licence Basic knowledge for categories A, B1 and B2 are indicated by the allocation of knowledge levels indicators (1, 2 or 3) against each applicable subject. Category C applicants must meet either the category B1 or the category B2 basic knowledge levels. The knowledge level indicators are defined as follows: LEVEL 1 Objectives: The applicant should be familiar with the basic elements of the subject. The applicant should be able to give a simple description of the whole subject, using common words and examples. The applicant should be able to use typical terms. LEVEL 2 A general knowledge of the theoretical and practical aspects of the subject. An ability to apply that knowledge. Objectives: The applicant should be able to understand the theoretical fundamentals of the subject. The applicant should be able to give a general description of the subject using, as appropriate, typical examples. The applicant should be able to use mathematical formulae in conjunction with physical laws describing the subject. The applicant should be able to read and understand sketches, drawings and schematics describing the subject. The applicant should be able to apply his knowledge in a practical manner using detailed procedures. LEVEL 3 A detailed knowledge of the theoretical and practical aspects of the subject. A capacity to combine and apply the separate elements of knowledge in a logical and comprehensive manner. Objectives: The applicant should know the theory of the subject and interrelationships with other subjects. The applicant should be able to give a detailed description of the subject using theoretical fundamentals and specific examples. The applicant should understand and be able to use mathematical formulae related to the subject. The applicant should be able to read, understand and prepare sketches, simple drawings and schematics describing the subject. The applicant should be able to apply his knowledge in a practical manner using manufacturer's instructions. The applicant should be able to interpret results from various sources and measurements and apply corrective action where appropriate. 2023-01-12 B-09 Human Factors Page 3 of 340 CASA Part 66 - Training Materials Only  Table of Contents Human Factors - General (9.1) 14 Learning Objectives 14 Summary 14 The Need to Take Human Factors into Account 15 What Is Meant by the Term Human Factors? 15 Human and Environmental Attributes Included in Human Factors Awareness 17 Why Study Human Factors? 18 Short History of CRM and HF Training 19 The SHELL Model 20 The Interface Between Each SHELL Model Component 21 Incidents Attributable to Human Factors / Human Error 25 Human Failure vs Other Causes 25 Human-Related Maintenance Causes of Significant Accidents 25 Case Study Examples of Incidents and Accidents 27 Characteristics of the Case Studies 30 Good People Doing Good Work 31 The Error Chain 32 The 'Swiss Cheese' Model 33 Murphy’s Law 35 Murphy’s Law and Human Complacency 35 Murphy-Proofing 35 Promote 'Constructive Worrying' 36 Human Errors in Aircraft Maintenance Are Not Random 38 Strategies for Error Management 39 Vision and Hearing (9.2.1-2) 41 Learning Objectives 41 Introduction 42 Summary 42 Human Performance Limitations Must be Taken into Account 42 Vision 45 Factors Affecting Clarity of Sight 45 Physical Factors 46 Environmental Factors 48 The Nature and Angle of the Object Being Viewed 50 2023-01-12 B-09 Human Factors Page 4 of 340 CASA Part 66 - Training Materials Only  Ingestion of Foreign Substances that Affect Eyesight 54 Vision for Aircraft Maintenance 55 Ambient and Task Lighting 56 Hearing 58 Performance and Limitations of the Ear 58 Impact of Noise on Hearing 58 Hearing Impairment 59 Presbycusis 61 Hearing Protection 61 Hearing Awareness When Conducting Aircraft Maintenance 62 Information Processing and Attention and Perception (9.2.3-4) 64 Learning Objectives 64 Summary 64 Information Processing 65 An Information Processing Model 65 Sensory Receptors and Short-Term Sensory Memory 65 Attention and Perception 67 Attention 67 Factors Affecting Attention 68 Perception 68 Situational Awareness 69 Decision-Making 70 Memory, Claustrophobia and Physical Access (9.2.5-6) 73 Learning Objectives 73 Memory 74 Summary 74 Memory Processes 74 Types of Memory 74 Motor Programs 76 Situational Awareness in Aircraft Maintenance 77 Information Processing Limitations 79 Deficiencies in Attention and Perception 80 Biases and Expectations 81 Memory Limitations 84 The Danger in Relying on Memory in Aircraft Maintenance 85 Claustrophobia and Physical Access 87 Introduction 87 2023-01-12 B-09 Human Factors Page 5 of 340 CASA Part 66 - Training Materials Only  Claustrophobia 87 Confined Space Access 87 Fear of Heights 88 Social Psychology (9.3) 90 Learning Objectives 90 Summary 90 Responsibility: Individual and Group 91 Introduction 91 Working as an Individual or within a Group 91 Individual Responsibility 92 Group or Team Responsibility 93 Motivation and Demotivation 96 Introduction 96 External and Internal Motivation 97 What Do People Want from Work? 97 Maslow’s Hierarchy of Needs 98 Demotivation 100 Personal Characteristics 101 Dealing with People with Conflicting Motivations 102 Peer Pressure 104 Introduction 104 Positive and Negative Peer Pressure and Conformity 105 Culture Issues 107 Aspects of Organisational Culture 107 Influences on Organisational Culture 108 Safety Culture 108 Key Components of a Safety Culture 110 Social Culture 111 Just Culture and Reporting Culture 112 The Blame Cycle 114 Blame Free Culture is not Desirable 117 Liability, Culpability and Employer’s Expectations 117 Disciplinary Policy 118 The Substitution Test 119 Culpability 120 Team Work 122 What is a Team? 122 2023-01-12 B-09 Human Factors Page 6 of 340 CASA Part 66 - Training Materials Only  Team Work 122 Important Elements of Team Work 124 Management, Supervision and Leadership 126 Managers and Supervisors 126 Characteristics of a Leader 127 Fitness, Stress and Time Pressure (9.4.1-3) 131 Learning Objectives 131 Summary 131 Overall Fitness and Health 132 Introduction 132 Pre-employment Health 133 Fitness to Conduct Aircraft Maintenance 134 Positive Measures to Maintain Health 135 An Ideal Diet 136 Hydration 137 Dehydration 138 Replenishing Fluids 139 Stress: Domestic and Work-Related 141 Introduction 141 Acute or Chronic Stress 141 Causes and Symptoms of Stress 141 Types of Stressors 142 Effects of Stress 143 Domestic Stress 144 Work-Related Stress 145 Stress Management 146 Strategies for Coping with or Defusing Stress 147 Time Pressure and Deadlines 149 Introduction 149 Operational Conflict 149 The Effects of Time Pressure and Deadlines 150 Managing Time Pressure and Deadlines 150 Workload, Sleep and Alcohol, Drugs and Drug Abuse (9.4.4-6) 152 Learning Objectives 152 Workload: Overload and Underload 153 Introduction 153 Factors Determining Workload 154 2023-01-12 B-09 Human Factors Page 7 of 340 CASA Part 66 - Training Materials Only  Overload 155 Coping with Overload 155 Underload 157 Workload Management 158 Sleep, Fatigue and Shift Work 160 Sleep 160 Sleep Cycles 161 Circadian Rhythms 162 Quality of Sleep 164 Age and Sleep 165 Informal Sleep 165 Sleep Disorders 167 Fatigue 167 Causes of Fatigue 168 Potential Effects of Fatigue on Performance 171 Personal Management of Fatigue and Performance 172 Shift Work 173 Rolling Shift Patterns 175 Alcohol, Medication and Drug Abuse 177 Precautions and Responsibilities 177 Alcohol 177 Medication 179 Drugs 180 Tobacco 181 Prescription Drugs 182 Drug and Alcohol Management Plan (DAMP) 182 Physical Environment (9.5) 184 Learning Objectives 184 Summary 184 Noise and Fumes 185 Noise 185 Fumes 186 Illumination 188 The Need for Light 188 Ambient Lighting 188 Task Lighting 189 Climate and Temperature 191 2023-01-12 B-09 Human Factors Page 8 of 340 CASA Part 66 - Training Materials Only  Human Performance Outside a Comfortable Temperature Range 191 Operational Pressures 192 Motion and Vibration 193 Motion When Working at Heights 193 Inspection Tasks 193 Vibration 194 Working Environment 195 Working Safely and Efficiently 195 Suitability of the Working Environment 195 Components of the Working Environment 197 Safety in the Working Environment 198 Confined Spaces 199 Working at Heights 199 Workplace Layout and Signage 200 Working Outdoors 200 Training and Personal Protective Equipment (PPE) 201 Physical Work and Repetitive Tasks (9.6.1-2) 203 Learning Objectives 203 Summary 203 Physical Work 204 Planning for the Work 204 Resources 204 Skills and Proficiency Required 205 Physical Tasks 205 Physical Condition of Workers 206 Design of Aircraft to Allow Access 206 Tools to Help with Physical Tasks 207 Fatigue 208 Repetitive Tasks 209 Introduction 209 Beware of Bias, Complacency and Assumptions 209 Visual Inspection and Complex Systems (9.6.3-4) 211 Learning Objectives 211 Visual Inspection 212 Eyesight 212 Visual Aids 212 Other Senses to Assist Visual Inspection 212 2023-01-12 B-09 Human Factors Page 9 of 340 CASA Part 66 - Training Materials Only  Reference Information 214 Introduction 214 Conducting the Visual Inspection 214 Preparation 215 Systematic Inspection 216 Finish 217 Concentration for Visual Inspection 217 Visual Techniques with Non-destructive Inspection 218 The Physical Environment Can Affect Visual Inspection 218 Complex Systems 220 Inputs, Processing, Response and Outputs 220 Procedures, Data and Reference Material 220 Communication Within and Between Teams (9.7.1) 222 Learning Objectives 222 Summary 222 Within and Between Teams 223 Communication to Assist Teamwork 223 What do we Communicate? 223 How do we Communicate? 223 Types of Communication 225 Communication within Teams 228 Communication between Teams 229 Shift Handover 230 Task Handover 241 Communication Problems 245 Work Logging and Recording (9.7.2) 248 Learning Objectives 248 Work Logging and Recording 249 Chances for Uncertainty and Miscommunication 249 How and When to Record Information 249 Words and Pictures 249 Recording Information for Handover and Complex Tasks 250 Electronic Ways of Recording 251 Keeping Up to Date, Currency and Dissemination of Information (9.7.3-4) 253 Learning Objectives 253 Keeping Up to Date, Currency 254 2023-01-12 B-09 Human Factors Page 10 of 340 CASA Part 66 - Training Materials Only  New Information 254 Ways of Keeping Current 254 Continuing Professional Development 255 Dissemination of Information 258 Shared Responsibility 258 Distributing and Checking for New Information 258 Error Models and Theories (9.8.1) 260 Learning Objectives 260 Summary 260 Error Models and Theories 261 Types of Human Error 261 Design versus Operator - Induced Errors 261 Variable versus Constant Errors 264 Reversible versus Irreversible Errors 264 Slips, Lapses and Mistakes 265 Misperceptions 266 Violations 267 Skill-, Rule- and Knowledge-Based Behaviours and Associated Errors 268 Memory Failures 271 Memory Input Failures 272 Memory Storage Failures 273 Memory Retrieval Failures 274 Failures Due to Attention 275 Common Errors in Aircraft Maintenance 276 The ‘Swiss Cheese Model’ 278 Types of Error in Maintenance Tasks (9.8.2) 281 Learning Objectives 281 Types of Errors in Maintenance Tasks 282 Errors During Maintenance Tasks 282 Errors Due to Individual Practices and Habits 283 Violations in Aircraft Maintenance 284 Why People Violate Rules 287 How Violations Differ from Errors 291 Main Causes of Error in Aircraft Maintenance 292 Implications, Avoiding and Managing Errors (9.8.3-4) 295 Learning Objectives 295 Implications of Errors 296 2023-01-12 B-09 Human Factors Page 11 of 340 CASA Part 66 - Training Materials Only  Incidents and Accidents 296 Reporting 297 Avoiding and Managing Errors 300 Introduction 300 Error Management 300 The Importance of Following Approved Procedures 301 Responsibility for Error Management 301 Error Management Systems 302 Proactivity and Reactivity 303 The Targets of Error Management 304 Changing the Future 307 Maintenance Error Decision Aid (MEDA) 308 The MEDA Process 310 Maintaining Safety in Aviation 312 Recognising and Avoiding Hazards (9.9.1) 316 Learning Objectives 316 Summary 316 Recognising and Avoiding Hazards 317 Potential Hazards in Aircraft Maintenance 317 Workplace Health and Safety Legislation 317 Maintenance and Repair (MRO) Organisation Responsibilities 318 Warning Signs 319 Maintenance Workers' Individual Responsibilities 321 Safety in the Aircraft Maintenance Environment 322 Safety When Working on Aircraft 323 Dealing with Emergencies (9.9.2) 325 Learning Objectives 325 Dealing with Emergencies 326 Types of Emergencies 326 Actions in an Emergency 326 Practice for an Emergency 328 Safety Management in Your Organisation (9.9.3) 329 Learning Objectives 329 Safety Management in Your Organisation 330 Safety Management System (SMS) 330 Risk Assessment and Management 331 Steps for Conducting Risk Assessment 332 2023-01-12 B-09 Human Factors Page 12 of 340 CASA Part 66 - Training Materials Only  'Just' Culture 334 Disciplinary Policy 335 Reporting Errors 335 Error Investigation 336 Action to Address Problems 337 Feedback to Employees 338 Human Factors Training Program 338 HF Continuation Training 338 2023-01-12 B-09 Human Factors Page 13 of 340 CASA Part 66 - Training Materials Only  Human Factors - General (9.1) Learning Objectives 9.1.1.1 Describe the need to take human factors into account (Level 2). 9.1.1.2 Compare and contrast HF for maintenance with flight crew CRM (Level 2). 9.1.2 Describe typical examples of aviation incidents attributable to human factors and human error (Level 2). 9.1.3.1 Explain Murphy's Law and give an example of how it applies in an aircraft maintenance environment (Level 2). 9.1.3.2 Describe a simple strategy for 'Murphy-proofing' (Level 2). Summary This topic introduces the term Human Factors (HF) and explains its importance within the aviation industry. This training course will be the initial introduction to the subject, but employees will be regularly refreshed in their HF knowledge and competence throughout their careers. The subject examines the relationship between humans and incidents or accidents in terms of human error. It also discusses 'Murphy’s Law', which states ‘if something can possibly go wrong, then one day it will go wrong’. 2023-01-12 B-09 Human Factors Page 14 of 340 CASA Part 66 - Training Materials Only  The Need to Take Human Factors into Account What Is Meant by the Term Human Factors? In aviation, human error is responsible for operational incidents and accidents. The study of human factors in aircraft maintenance seeks to examine the people, environment, the actions and resources involved in the conduct of aircraft maintenance. It recognises that humans make mistakes and don’t work well under some conditions. Further, it seeks to challenge and, if possible, rectify the chance for poor human performance, including errors, to have aviation safety consequences, including operational incidents and accidents. Image by Marcelino James from Pixabay Aircraft on ramp Human factors in aircraft maintenance are an evolution of the original Cockpit Resource Management (CRM) awareness training that was introduced for commercial pilots in the 1970s. This training later included cabin crew and was referred to as Crew Resource Management. CRM was introduced to reduce incidents and accidents attributable to human error, or to poor human interaction, such as in communication or teamwork. It was determined that other job roles in the aviation system were also susceptible to human error and poor human interaction, with the potential to cause undesirable incidents and accidents. Human factors training was then adapted to these other job roles, including aircraft maintenance. 2023-01-12 B-09 Human Factors Page 15 of 340 CASA Part 66 - Training Materials Only  Aircraft maintenance personnel work in a vastly different environment to flight crew and cabin crew. Therefore, HF training for maintenance professionals is very different to CRM. Some of the theory of human physiology and behaviour is common across all groups, but each job role has different tasks, different resources, and different environmental conditions. Image by Eugen Visan from Pixabay Pilot at flight deck window There are many definitions of HF available. A simple definition could be: Human factors refers to the study of human capabilities and limitations in the workplace. In aircraft maintenance, this study centres on the interaction among maintenance personnel, the equipment they use, the written and verbal procedures and rules they follow, and the environmental conditions of their system. 2023-01-12 B-09 Human Factors Page 16 of 340 CASA Part 66 - Training Materials Only  Image by David Mark from Pixabay Engine maintenance The aim of human factors for aircraft maintenance could be written: "To optimise the relationship between maintenance personnel and systems with a view to improving safety, efficiency and well-being." 2023-01-12 B-09 Human Factors Page 17 of 340 CASA Part 66 - Training Materials Only  Human and Environmental Attributes Included in Human Factors Awareness Human factors include such attributes as: Human physiology Psychology (including perception, cognition, memory, social interaction) Workplace design Environmental conditions Human-machine interface Anthropometrics (the scientific study of measurements of the human body). Image by delo from Pixabay Propeller maintenance 2023-01-12 B-09 Human Factors Page 18 of 340 CASA Part 66 - Training Materials Only  Why Study Human Factors? The aviation regulators insist that we study human factors because the human is the most unreliable piece of the aviation system. Aircraft and other machinery have become more sophisticated and reliable, but humans will always make mistakes. This imperfection is part of being human and can never be entirely eliminated. HF training seeks to make people aware of these limitations, and to examine the organisations where the work is carried out, so that mechanisms may be put in place to capture human error before it can have bad consequences. An understanding of the importance of human factors to aircraft maintenance engineering is essential to anyone considering a career as an, Aircraft Maintenance Engineer (AME) or working in the many support or managerial roles within a Maintenance and Repair Organisation (MRO). This is because human factors will affect everything they do in the course of their job in one way or another. 2023-01-12 B-09 Human Factors Page 19 of 340 CASA Part 66 - Training Materials Only  Short History of CRM and HF Training As early aircraft evolved into more complex machines, systems were designed to complement the human abilities of pilots, so the need for consideration of human/machine interface became apparent, as did the need for maintenance personnel to have more and more complex skills and knowledge from maintenance personnel. From the very early days it was obvious, mistakes made when designing, building, controlling or maintaining aircraft could lead to catastrophic results. Over time, it became clear that, no matter how experienced or well-trained, no person is infallible. Expensive and tragic accidents in aviation were consistently attributable to human error. For human factors in aircraft maintenance, significant accidents in the 1970s, 1980s and 1990s highlighted the fact that aircraft maintenance is a highly technical job, particularly dependent on knowledge and skill. It became evident that the job of ensuring the safety of the aircraft is extremely sensitive to human error, but the nature of the work and the environment in which the work is conducted makes it almost inevitable that errors will occur. Photo by Austrian National Library on Unsplash Historical aircraft parts manufacturing 2023-01-12 B-09 Human Factors Page 20 of 340 CASA Part 66 - Training Materials Only  The SHELL Model When trying to understand the nature of work in aircraft maintenance, and how to develop strategies to make the work safer, it is often useful to consult a model. A common model to explain the interactions in any complex environment is the SHELL model. © Aviation Australia SHELL Model 2023-01-12 B-09 Human Factors Page 21 of 340 CASA Part 66 - Training Materials Only  The Interface Between Each SHELL Model Component The study of human factors focuses on the interfaces between the human individual (the 'L' in the centre) and the other elements of the SHELL Model. The SHELL Model provides an overview of human factors by showing how humans interact with all other things in the workplace and life in general: The SHELL elements are: Software - For example, maintenance procedures, maintenance manuals, checklist layout, etc. Hardware - For example, tools, test equipment, the physical structure of aircraft, design issues, warning and lockout devices, equipment maintenance etc. Environment - For example, physical environment such as conditions in the hangar, conditions on the line, etc. and work environment such as work patterns, management structures, public perception of the industry, etc. Liveware - The individuals or groups of people with whom a person has to interact. For example, supervisors, customers, team members. Liveware - The person or people at the centre of the model and their own physical and psychological strengths and limitations. Sometimes the interfaces between elements are shown as blurred or wavy lines to indicate the interface is never perfect. This represents how errors can occur. © Aviation Australia SHELL Model (Imperfect) 2023-01-12 B-09 Human Factors Page 22 of 340 CASA Part 66 - Training Materials Only  For example: S - misinterpretation of procedures, badly written manuals, poorly designed checklists, untested or difficult to use computer software. H - not enough tools, people not trained to use tools, inappropriate equipment, poor aircraft design for maintainability. E - uncomfortable workplace, inadequate hangar space, extreme temperatures, excessive noise, poor lighting. L - relationships with other people, shortage of manpower, lack of supervision, lack of support from managers. Since Liveware is at the centre of the model, all other aspects (Software, Hardware and Environment) must be designed or adapted to assist human performance and respect human limitations. If these two aspects are ignored, the human, in this case the maintenance engineer, will not perform to the best of their abilities and may make errors or jeopardise safety. The goal when studying how humans interact with other aspects of their work environment is to improve these relationships, which will improve efficiency and safety. Thanks to modern design and manufacturing standards, aircraft are becoming more and more reliable. However, it is not possible to redesign the human being. We can educate, train, mentor and support people in certain ways, but we must accept the fact that the human being is fundamentally unreliable. We can challenge that unreliability by providing procedures and tools, performing Independent Inspections, etc. We can also reduce the potential for error by improving aircraft design such that, for example, it is physically impossible to reconnect something the wrong way around. This is known as 'Murphy-proofing' and is discussed further in this course. These measures are implemented to support people when doing their job and attempt to minimise errors. But if errors cannot be eliminated, then implementing procedures and other interventions can help capture human errors before they can do any harm. 2023-01-12 B-09 Human Factors Page 23 of 340 CASA Part 66 - Training Materials Only  Image by Dirk Wouters from Pixabay Measures can be implemented to support people when doing their job. 2023-01-12 B-09 Human Factors Page 24 of 340 CASA Part 66 - Training Materials Only  Incidents Attributable to Human Factors / Human Error Human Failure vs Other Causes Boeing have reported that in the early days of flight, approximately 80% of accidents were caused by the machine and 20% were caused by human error. Today that statistic has reversed. Approximately 80% of airplane accidents are due to human error (pilots, air traffic controllers, mechanics, etc.) and 20% are due to machine (equipment) failures. © Aviation Australia Incidents attributable to human factors/human error. In a further breakdown, according to FAA, approximately 80% of all maintenance failures involve human factors and undetected maintenance failures often lead to accidents. Human-Related Maintenance Causes of Significant Accidents A detailed study (noted in UK CAA CAP 718) of 93 major world-wide accidents between 1959 and 1983- found that 12% of the accidents were attributed to maintenance and inspection factors (4th on the list). 2023-01-12 B-09 Human Factors Page 25 of 340 CASA Part 66 - Training Materials Only  Causes/major contributory factors % of accidents in which this was a factor Pilot deviated from basic operational procedures 33 Inadequate cross-check by second crew member 26 Design faults 13 Maintenance and inspection deficiencies 12 Absence of approach guidance 10 Captain ignored crew inputs 10 Air traffic control failures or errors 9 Improper crew response during abnormal conditions 9 Insufficient or incorrect weather information 8 Runway hazards 7 Air traffic control/crew communication deficiencies 6 Improper decision to land 6 The UK CAA carried out a similar exercise in 1998, looking at causes of 621 global fatal accidents between 1980 and 1996. Again, the area 'maintenance or repair oversight/error/inadequate' featured as one of the top 10 primary causal factors. It is clear from such studies that human factors problems, in aviation generally and aircraft maintenance engineering in particular, are a significant issue warranting serious consideration. As stated, the human is the most unreliable piece of the aviation system. Aircraft and other machinery have become more sophisticated and reliable, but humans will always tend to make mistakes. This imperfection is part of being human and can never be entirely eliminated. 2023-01-12 B-09 Human Factors Page 26 of 340 CASA Part 66 - Training Materials Only  Image by Frederik Schweiger on Unsplash Humans will always tend to make mistakes Case Study Examples of Incidents and Accidents This module describes a number of systematic failures and past incidents and accidents that have been important in highlighting human error in aircraft maintenance or have prompted changes in the way people work or how our industry operates. When referencing past incidents and accidents in these notes, the [CS] denoting 'Case Studies' will be applied to the title. Some of the case studies are listed below. If searching for resources related to these incidents, it is far more common to find videos, etc., related to the in-flight aspects of the event. You will often need to refine your search to find resources that describe the circumstances surrounding the maintenance of the aircraft involved. Aloha Airlines Flight 243, Boeing 737 in 1988 Accident en route to Maui, Hawaii on 28 April 1988; Section of upper fuselage structure ripped off in flight; Deficiency in structural inspection methods. 2023-01-12 B-09 Human Factors Page 27 of 340 CASA Part 66 - Training Materials Only  British Airways Flight 5390, BAC 1-11 in 1990 Accident near Didcot, UK, on 10 June 1990; Cockpit windscreen blew out in flight; Cockpit windscreen installed with many incorrect fasteners. Excalibur Airways Charter Flight, Airbus A320 in 1993 Incident on take-off from London Gatwick Airport on 26 August 1993; Uncommanded roll after take-off; Spoilers left in disabled mode after maintenance. British Midland Airways Charter Flight, Boeing 737 in 1995 Incident near Daventry, UK, on 23 February 1995; Loss of oil pressure in both engines; Engines not restored to correct condition after maintenance. Aloha Airlines Boeing 737 in 1988 In the accident involving Aloha Flight 243 in April 1988, an explosive cabin decompression occurred as 6 metres of the upper cabin fuselage structure were suddenly ripped away in flight due to structural failure. The Boeing 737 involved in this accident had been examined, as required by US regulations, by two of the engineering inspectors. One inspector had 22 years' experience and the other, the chief inspector, had 33 years' experience. Neither found any cracks in their inspection. Post-accident analysis determined there were over 240 cracks in the skin of this aircraft at the time of the inspection. The ensuing investigation identified many human-factors-related problems leading to the failed inspections. As a result of the Aloha accident, the US instigated a research program to examine the problems associated with human factors and aircraft maintenance, with particular emphasis upon inspection techniques and ageing aircraft. The full NTSB (US) accident investigation report can be found at: https://www.ntsb.gov/investigations/AccidentReports/Pages/AAR8903.aspx Relevant Youtube link: The accident on Aloha Airlines Flight 243 For more information, search: ‘Aloha Airlines flight 243’ 2023-01-12 B-09 Human Factors Page 28 of 340 CASA Part 66 - Training Materials Only  British Airways BAC 1-11 in 1990 On 10 June 1990 in the UK, a BAC 1-11, British Airways Flight 5390 was climbing through 5300 m on departure from Birmingham International Airport when the left windscreen, which had been replaced prior to the flight, was blown out under the effects of cabin pressure. The windscreen blew out when the cabin pressure overcame the securing bolts, of which 84 of a total of 90 were smaller than the specified diameter. The commander was sucked halfway out of the windscreen frame and was restrained by cabin crew while the co-pilot flew the aircraft to a safe landing at Southampton Airport. The Shift Maintenance Manager (SMM), undermanned on a night shift, had decided to carry out the windscreen replacement himself. He consulted the Aircraft Maintenance Manual (AMM) and concluded that it was a straightforward job. He decided to replace the old bolts and, taking one of the bolts with him (a 7D diameter bolt), he looked for replacements. The storeman advised him that the job required 8D diameter bolts, but since there were not enough 8Ds, the SMM decided that 7Ds would do, since these size bolts had been in place previously. However, he used sight and touch to match the bolts and incorrectly selected 8Cs instead, which were longer but thinner. He failed to notice that the countersink was lower than it should be once the bolts were in position. He completed the job himself and certified for the task, the procedures not requiring a pressure check or Independent Inspection. Several human factors issues contributed to this incident, including perceptual errors made by the SMM when identifying the replacement bolts, poor lighting in the stores area, failure to wear spectacles, circadian effects, working practices, and possible organisational and design factors. The full AAIB (UK) accident investigation report can be found at: https://www.gov.uk/aaib-reports/1- 1992-bac-one-eleven-g-bjrt-10-june-1990 For more information search: ‘British Airways flight 5390’. 2023-01-12 B-09 Human Factors Page 29 of 340 CASA Part 66 - Training Materials Only  Excalibur Airways Airbus A320 in 1993 An incident in the UK in August 1993 involved a charter airline Airbus A320 which, during its first flight after a flap change, exhibited an uncommanded roll to the right after take-off. The aircraft returned to Gatwick and landed safely. The investigation discovered that during maintenance, in order to replace the right outboard flap, the spoilers had been placed in maintenance mode and moved using an incomplete procedure. Specifically, locking collars and flags were not fitted to the spoilers. The purpose of the collars and the way in which the spoilers functioned was not fully understood by the AMEs. This misunderstanding was due, in part, to familiarity of the engineers with another aircraft type. This contributed to a lack of adequate briefing on the status of the spoilers during the shift handover. The locked spoiler was not detected during standard pilot functional checks. The full AAIB (UK) accident investigation report can be found at: https://www.gov.uk/aaib-reports/2- 1995-airbus-a320-212-g-kmam-26-august-1993 For more information search: ‘Excalibur Airways Airbus A320’ British Midland Airways Boeing 737 in 1995 In the UK in February 1995, a British Midland Airways Boeing 737-400 suffered a loss of oil pressure in both engines. The aircraft diverted and landed safely at Luton Airport. The investigation discovered that borescope inspections had been carried out on both aircraft engines during the preceding night. The investigation also found the high pressure (HP) rotor drive covers had not been refitted, resulting in the loss of almost all the oil from both engines during flight. A line engineer was originally going to carry out the task, but for various reasons he swapped jobs with the base maintenance controller. The base maintenance controller did not have the appropriate paperwork with him. The base maintenance controller and a fitter completed the work despite many interruptions, but failed to refit the rotor drive covers. No ground idle engine runs were carried out. This step would have revealed an oil leak with the drive covers not fitted. The job was certified as complete. The full AAIB (UK) accident investigation report can be found at: https://www.gov.uk/aaib-reports/3- 1996-boeing-737-400-g-obmm-23-february-1995 For more information search: ‘British Midland engine failure Luton’ 2023-01-12 B-09 Human Factors Page 30 of 340 CASA Part 66 - Training Materials Only  Characteristics of the Case Studies In all of these incidents, the engineers involved were considered by their companies to be well qualified, competent and reliable employees. They were working within the expectations of their employers. All of the incidents were characterised by the following: There were staff shortages; Time pressures existed; Errors occurred at night or under poor inspection conditions; Shift or task handovers were involved; They involved supervisors doing long hands-on tasks; There was an element of a 'can-do' attitude; The inspections and tasks were characterised by interruptions; There was some failure to use approved data or company procedures; Manuals and other maintenance documentation were confusing; and There was inadequate pre-planning, equipment or spares. Incidents and Accidents Should Serve to Improve Standards The errors shown in the four case studies above are very common when studying human factors in aircraft maintenance. They all involve human performance deficiencies and, like many incidents and accidents, have served to improve standards in the industry and initiate changes in procedure. Some additional relevant case studies are given in Module 9.8 of this course. 2023-01-12 B-09 Human Factors Page 31 of 340 CASA Part 66 - Training Materials Only  Good People Doing Good Work Most incidents and accidents involve good people trying to do the right thing. In all the examples above, the incident or accident involved good people trying to do the right thing, but falling short in some way. All these incidents were preventable and could have been avoided if any one of a number of things had been done differently. In some cases, several individuals were involved, and the outcome could have been different if any one of them had reacted or queried a particular action. In each situation, the individuals failed to recognise or react to signs of potential hazards, did not react as they would normally be expected to, or allowed themselves to be distracted or diverted from giving their attention to the task in hand. By doing these things, they left themselves open to a greater likelihood of committing an error. Image by Miguel A. Amutio on Unsplash Incidents or accidents can be caused by good people trying to do the right thing, but falling short. 2023-01-12 B-09 Human Factors Page 32 of 340 CASA Part 66 - Training Materials Only  The Error Chain The error chain represents a series of events that lead to an incident or accident. As with many incidents and accidents, the examples given above all involve a series of problems which formed an error chain. When complete, the links in the chain allowed errors to progress causing an incident or accident. However, if any of the links in this chain had been broken, these incidents may have been prevented. Additional safety measures built into the organisation and maintenance processes, such as better procedures, enhanced inspection methods or better training, would contribute to breaking the error chain. Image by Clker-Free-Vector-Images from Pixabay Breaking the error chain Accidents result from a chain of events. If the error chain is broken, incidents and accidents are prevented. 2023-01-12 B-09 Human Factors Page 33 of 340 CASA Part 66 - Training Materials Only  The 'Swiss Cheese' Model The error chain can also be explained by Professor James Reason's well-known 'Swiss Cheese' Model of accident causation. In this model, the slices or layers of Swiss cheese represent barriers of defence between hazards or errors and the bad consequences possibly arising from those errors, e.g. accidents. Like the error chain, barriers might represent better procedures, enhanced inspection methods, better training or other enhancements. Any of the barriers has the ability to prevent an accident from occurring. But, like Swiss cheese, the barriers are usually not perfect, or complete. They have deficiencies, represented by holes, which allow the hazard situation to move progressively closer to causing undesirable consequences. If circumstances allow all the holes in the layers of defence to line up, then a particular hazard will cause an undesirable event: an incident or accident. Model created by Dante Orlandella and James T. Reason of the University of Manchester Reason's Swiss Cheese Model 2023-01-12 B-09 Human Factors Page 34 of 340 CASA Part 66 - Training Materials Only  Murphy’s Law Murphy’s Law and Human Complacency A common way of expressing Murphy’s Law is: “If something can go wrong, it will.” The belief that an accident will never happen to me or to my company can be a major problem when attempting to inform individuals or organisations about human factors issues, to recognise risks and to implement improvements. It is necessary to make human factors issues relevant and important rather than merely paying lip service to them. Complicating Murphy’s Law, there is a tendency among human beings towards complacency. Complacency is sometimes described as a feeling of security while unaware of some potential danger or defect. Complacency in aircraft maintenance may come about because an organisation is very safe and the maintenance workers have never experienced an accident or incident. Thus, they may feel as though because an accident HAS NEVER happened, an accident WILL NEVER happen. The belief that an accident will never happen to me or to my company can be a major problem when attempting to inform individuals or organisations about human factors issues, where the challenge is to recognise risks and to implement improvements. Image by William Daigneault from Unsplash The belief that an accident will never happen to me can be a major problem. 2023-01-12 B-09 Human Factors Page 35 of 340 CASA Part 66 - Training Materials Only  Murphy-Proofing Defences against Murphy’s Law are often known as ‘Murphy-proofing’ (sometimes called ‘poka- yoke’). For example, the two identical electrical connectors are side by side, and it is physically possible for the connectors to be reversed, i.e. the left-hand connector can be fitted to the right-hand receptacle, then from the paragraph above, Murphy's Law says this mistake of mis-connecting the wiring will eventually happen. Murphy-proofing in this situation may mean replacing one of the connectors with a connector of different size or shape, meaning that reversing the connectors is not physically possible. © Jonathan Trout, Noria Corporation modified by Aviation Australia Error elimination by design 2023-01-12 B-09 Human Factors Page 36 of 340 CASA Part 66 - Training Materials Only  Promote 'Constructive Worrying' Complacency in aircraft maintenance is dangerous. Keep thinking about ways to improve. If everyone could be persuaded to acknowledge Murphy’s Law, this might help overcome the complacent belief that accidents will never happen. It is certainly not true that accidents happen only to people who are irresponsible or sloppy. Some errors are unavoidable due to poor design, organisational pressure or other underlying factors. Image by Scottslm from Pixabay Keep thinking about ways to improve. The incidents and accidents described show that errors can be made by experienced, well-respected individuals and that accidents can occur in organisations previously thought to be safe. When working in an organisation that hasn't had a workplace incident or accident for a long time, the sense of complacency can be magnified. To combat this, a conscious effort needs to be made to keep thinking that a bad accident is just around the corner and to keep trying to proactively improve workplace conditions and procedures. 2023-01-12 B-09 Human Factors Page 37 of 340 CASA Part 66 - Training Materials Only  Image by skeeze from Pixabay Maintenance environment can contribute to complacency. 2023-01-12 B-09 Human Factors Page 38 of 340 CASA Part 66 - Training Materials Only  Human Errors in Aircraft Maintenance Are Not Random Past human factors research has shown that maintenance-related errors are not random events. They fall into recurrent patterns shaped by situation and task factors characteristic of maintenance activities in general. For example, if a task has a complex, multi-step process, then it is well known that people cannot remember too many steps without memory aids. So, it is good practice to provide a detailed checklist for workers to follow. It is also good practice to alert other members of the working group not to interrupt these people when they are concentrating on their complex task. Human limitations are obvious in many aircraft maintenance situations. Once you have worked in the industry for a while, you will recognise the potential for error in the aircraft maintenance system. For example, aircraft maintenance often involves people conducting detailed inspections in the middle of the night. Considering humans are not nocturnal animals, this situation is not ideal. Image by Soumya Ranjan from Pexels Aircraft maintenance often involves people conducting detailed inspections in the middle of the night. Errors are not committed by a few careless or incompetent individuals. One of the basic principles of error management is that the best people can make the worst mistakes. Data shows that different people in different organisations keep on making the same mistakes. Because of this, we can leverage well-defined business risk processes to focus limited resources for maximum remedial effect. 2023-01-12 B-09 Human Factors Page 39 of 340 CASA Part 66 - Training Materials Only  Strategies for Error Management Human performance is part of the aircraft maintenance system, so it must be accounted for. Human limitations may be countered through strategic design of the workplace, work practices and machines. It should be stressed, however, that there is no single best way of limiting and containing human error. Effective error management requires a wide variety of countermeasures directed at different levels of the system: The individual The team The task The workplace The organisation as a whole. © Aviation Australia Strategies for Error Management This training material is one strategy to highlight the causes and effects of human error as well as ways to contain it. Your awareness of human factors is critical to how you perform the important work of aircraft maintenance. 2023-01-12 B-09 Human Factors Page 40 of 340 CASA Part 66 - Training Materials Only  Vision and Hearing (9.2.1-2) Learning Objectives 9.2.1 Explain the importance of vision to aircraft maintenance workers and how vision may be affected in individuals and under certain conditions (Level 2). 9.2.2.1 Explain the importance of hearing to aircraft maintenance workers and how hearing may be affected in individuals and under certain conditions (Level 2). 9.2.2.2 Describe strategies for protecting hearing in an aircraft maintenance environment (Level 2). 2023-01-12 B-09 Human Factors Page 41 of 340 CASA Part 66 - Training Materials Only  Introduction Summary Humans are very capable animals, yet our capability has limitations. We perform poorly at night and in the cold. We are sometimes not strong enough, or our vision is not sharp enough and we need tools to assist us. We often cannot remember things and our brain does not work well when we are under stress or dealing with competing priorities. The intention of this chapter is to provide an overview of those key physical and mental human performance characteristics which are likely to affect an aircraft maintenance engineer in their working environment, such as vision, hearing, information processing, attention and perception, memory, judgement and decision-making. 2023-01-12 B-09 Human Factors Page 42 of 340 CASA Part 66 - Training Materials Only  Human Performance Limitations Must be Taken into Account Humans are an integral part of the maintenance engineering system, so human performance limitations must be taken into account when considering aircraft maintenance and workplace safety. Just as certain mechanical components used in aircraft maintenance engineering have limitations, engineers themselves have certain capabilities and limitations that must be considered when looking at the maintenance engineering system. Rivets will eventually fail if enough force is applied to them. The same principles apply to human performance, which is likely to degrade and eventually ‘fail’ under certain conditions (e.g., stress). Humans are limited by our physiology and psychology. Humans need tools, vehicles, clothes, air conditioning, computers and Personal Protective Equipment (PPE) all because we lack physical or mental characteristics that are needed to do certain tasks. People can also fail to function properly in certain situations. Physically, humans become fatigued, are affected by the cold, can break bones in workplace accidents and suffer other physical ailments. Mentally, humans can make errors, have limited perceptual powers and can exhibit poor judgement due to lack of skills and knowledge. Unlike mechanical components, human performance is also affected by social and emotional factors. Failure by aircraft maintenance personnel will likely be to the detriment of aircraft safety. Image by Herry Sutanto on Unsplash Humans are limited by our physiology and psychology 2023-01-12 B-09 Human Factors Page 43 of 340 CASA Part 66 - Training Materials Only  The AME is the central part of the aircraft maintenance system. It is therefore very useful to have an understanding of how various parts of their body and mental processes function and how performance limitations can influence their effectiveness at work. Image by Maria Teneva on Unsplash People can also fail to function properly in certain situations 2023-01-12 B-09 Human Factors Page 44 of 340 CASA Part 66 - Training Materials Only  Vision Factors Affecting Clarity of Sight The eye is very sensitive in the right conditions (e.g. clear air, good light). The eye has approximately 1.2 million nerve cells leading from the retinas to the area of the brain responsible for vision, while there are only about 50 000 from the inner ears, making the human eye about 24 times more sensitive than the ear. Visual acuity is the ability of the eye to discriminate sharp detail at varying distances. Various factors can affect and limit the visual acuity of the eye. These include: Physical factors, such as: Physical imperfections in one or both eyes (short sightedness, long sightedness) Age. Environmental factors, such as: Amount of light available Clarity of the air (e.g., dust, mist, rain, etc.). Nature of the object being viewed, such as: Size and contours of the object Contrast of the object with its surroundings Relative motion of the object Vibration of the object Distance of the object from the viewer. The angle of the object from the viewer. The ingestion of foreign substances, such as: Drugs Medication Alcohol Cigarettes. 2023-01-12 B-09 Human Factors Page 45 of 340 CASA Part 66 - Training Materials Only  Image by Peter Heeling from Skitterphoto Various factors can affect and limit the visual acuity of the eye 2023-01-12 B-09 Human Factors Page 46 of 340 CASA Part 66 - Training Materials Only  Physical Factors Lens Imperfections Long sightedness is caused by a shorter than normal eyeball which means that the image is focused behind the retina. If the cornea and the lens cannot use their combined focusing ability to compensate for this, blurred vision will result when looking at close objects. A convex lens overcomes long sightedness by bending light inwards before it reaches the cornea. Short sightedness occurs when the eyeball is longer than normal, causing the image to be formed in front of the retina. If the accommodation of the lens cannot counteract this then distant objects are blurred. A concave lens overcomes short-sightedness by bending light outwards before it reaches the cornea. Image by Dani Link from Pixabay A concave lens overcomes short-sightedness by bending light outwards before it reaches the cornea 2023-01-12 B-09 Human Factors Page 47 of 340 CASA Part 66 - Training Materials Only  Ageing As a person grows older, the lens becomes less flexible meaning it is unable to adjust sufficiently. This is known as presbyopia and is a form of long sightedness. Consequently, after the age of 40, spectacles may be required for near vision, especially in poor light conditions. Fatigue can also temporarily affect the lens’ ability to accommodate, causing blurred vision for close work. Blind Spot The blind spot is a normal visual deficiency at the point where the optic nerve enters the retina (between the rods and cones). At this point the retina is not sensitive to any light shining on it. Facial features such as the nose can also contribute to this problem. Other Visual Imperfections include: Cataracts - clouding of the lens usually associated with exposure to UV light and ageing; Astigmatism - a misshapen cornea causing objects to appear irregularly shaped; Glaucoma - a build-up in pressure of the fluid within the eye which can cause damage to the optic nerve and even blindness; Migraine - severe headaches that can cause visual disturbances. 2023-01-12 B-09 Human Factors Page 48 of 340 CASA Part 66 - Training Materials Only  Environmental Factors Light Vision can be improved by increasing the lighting level, but only up to a point. Increased illumination often causes increased glare. Older people are more affected by the glare of reflected light than younger people. Moving from an extremely bright environment to a dimmer one has the effect of reducing vision being reduced until the eyes get used to less light being available. This is because the eyes become adapted to ambient light. Moving from a bright hangar, or from inside an aircraft, to a dark apron area at night can mean that maintenance workers must wait for their eyes to adapt to the lower ambient light. In low light conditions, it is often easier to focus if you look slightly to one side of an object. This allows the image to fall onto the part of the retina that has many rods. Image by Mihai Paraschiv from Pixabay Environmental factors like poor lighting can affect vision Airborne Particles Any particles in the air such as dust, rain or mist can interfere with the transmission of light through the air, distorting what is seen. This can be even worse when spectacles are worn, as they are susceptible to getting dirty, wet, misted up or scratched. 2023-01-12 B-09 Human Factors Page 49 of 340 CASA Part 66 - Training Materials Only  Contact Lenses in Dry and Dusty Atmospheric Conditions The maximum wear time for contact lenses is usually 8 to 12 hours. Extended wear may have adverse effects on the eyes, such as dryness and irritation. This is particularly important if working in an environment which is excessively dry or dusty, as airborne particles may also affect contact lens wear. Goggles should be worn where necessary to exclude dust from the eyes. 2023-01-12 B-09 Human Factors Page 50 of 340 CASA Part 66 - Training Materials Only  The Nature and Angle of the Object Being Viewed Size Visual cues often refer to the comparison of objects of known size to those of objects of unknown size. An example of this is that we learn as a child to associate small objects with being further away. In general terms, larger objects are more easily seen than smaller objects, but it is no use moving too close. There needs to be an appreciation of the micro and macro view. Contrast Similarly, if an object does not stand out well from its background (poor contrast with its surroundings), it is harder to distinguish its edges and hence its shape. Movement and Vibration Movement and relative motion of an object, as well as distance and angle of the object from the viewer, can increase visual demands. If the object, or the viewer is vibrating, then the view of the object will not be clear. Image by Johannes Rapprich from Pexels Movement and relative motion of an object can increase visual demands 2023-01-12 B-09 Human Factors Page 51 of 340 CASA Part 66 - Training Materials Only  Colour Although not directly affecting visual acuity, inability to see particular colours can be a problem for the aircraft maintenance engineer. Among other things, good colour vision for maintenance engineers is important for: Recognising components Distinguishing between electrical wires Using various diagnostic tools Recognising various lights on the airfield (e.g., warning lights). The most common type is colour vision deficiency is distinguishing between red and green. More rarely, it is possible to confuse blues and yellows. Ageing also causes changes in colour vision. This is a result of progressive yellowing of the lens, resulting in reduced colour discrimination in the blue-yellow range. Image by MichaelGaida from Pixabay Good colour vision for maintenance engineers is important for recognising tarmac markings 2023-01-12 B-09 Human Factors Page 52 of 340 CASA Part 66 - Training Materials Only  Colour Loss at Night Central vision is poor at night or with low illumination. Better results are obtained by looking slightly to one side of an object, rather than directly at it. This effect can be demonstrated by counting a group of faint lights in the distance when looking directly at them, then by looking some 10 degrees to one side. It will be possible to see more lights. Some people who have perfect day vision may be myopic (short-sighted) at night. Night myopia is often not recognised well by people who have it, but can present a significant hazard, particularly because of the false confidence instilled from having good vision by day. Image by skeeze from Pixabay Central vision is poor at night or with low illumination 2023-01-12 B-09 Human Factors Page 53 of 340 CASA Part 66 - Training Materials Only  The Angle of the Object from the Viewer Objects are never as clear when they are looked at from an angle, compared to front-on. In addition, the background behind an object may change if the observer changes position. This may affect the clarity of the object. ‘Parallax' refers to the way an object seems to change its position when your own point of observation changes. Instrument reading can suffer from parallax error if the instrument is not read from directly in front. Older instruments are particularly susceptible to this, as there is often a physical gap between the instrument pointer/needle and the face of the dial. Tel-Tru Parallax error 2023-01-12 B-09 Human Factors Page 54 of 340 CASA Part 66 - Training Materials Only  Ingestion of Foreign Substances that Affect Eyesight Vision can be adversely affected by using certain drugs and medications, drinking alcohol, and smoking cigarettes. With smoking, carbon monoxide builds up in the bloodstream allowing less oxygen to be carried in the blood to the eyes. This is known as hypoxia and can rapidly impair the sensitivity of the rods. Alcohol can have similar effects, even hours after the last drink. Image by Karolina Grabowska from Pexels Vision can be adversely affected by using certain drugs and medications 2023-01-12 B-09 Human Factors Page 55 of 340 CASA Part 66 - Training Materials Only  Vision for Aircraft Maintenance Vision is critical for aircraft maintenance, especially when conducting inspection tasks. It is important for maintenance workers, particularly those who are involved in inspection tasks, to have adequate vision to meet the task requirements. As discussed previously, age and problems developing in the eye itself can gradually affect vision. Without regular vision testing, AMEs may not notice that their vision is deteriorating. Often, airline companies or airports will set the eyesight standards for reasons other than aircraft maintenance safety, for insurance purposes, or for driving on the airfield. It is important for the individual to recognise when their vision is adversely affected, either temporarily or permanently, and to consider carefully the possible consequences should they continue to work if the task requires good vision. Photo by Adrian Smith on Unsplash It is important for the individual to recognise when their vision is adversely affected 2023-01-12 B-09 Human Factors Page 56 of 340 CASA Part 66 - Training Materials Only  Ambient and Task Lighting A maintenance organisation must provide a well-lit area for aircraft inspection tasks or provide supplementary lighting if the ambient lighting is not sufficient. Individual maintenance workers must ensure that illumination is adequate for the inspection tasks they must perform. Western Technology Task lighting 2023-01-12 B-09 Human Factors Page 57 of 340 CASA Part 66 - Training Materials Only  Hearing Performance and Limitations of the Ear The performance of the ear is associated with the range of sounds that can be heard, both in terms of the pitch (frequency) and the volume of the sound. The audible frequency range that a young person can hear is typically between 20 and 20 000 cycles per second or (Hertz), with greatest sensitivity at about 3000 Hz. Volume (or intensity) of sound is measured in decibels (dB). The audible frequency range that a young person can hear is typically between 20 and 20 000Hz 2023-01-12 B-09 Human Factors Page 58 of 340 CASA Part 66 - Training Materials Only  Impact of Noise on Hearing Noise can have various negative effects in the workplace. It can: Be annoying (e.g. sudden sounds, constant loud sound). Interfere with verbal communication between individuals in the workplace. Cause accidents by masking warning signals or messages. Be fatiguing and affect concentration, decision-making. Damage workers’ hearing (either temporarily or permanently). Intermittent and sudden noise are generally considered to be more disruptive than continuous noise at the same level. In addition, high frequency noise generally has a more adverse effect on performance than lower frequency. Noise tends to increase errors and variability rather than directly affect work rate. Image by @chairulfajar from Unsplash. Noise can damage workers’ hearing (either temporarily or permanently) 2023-01-12 B-09 Human Factors Page 59 of 340 CASA Part 66 - Training Materials Only  Hearing Impairment Hearing loss can result from exposure to noise of even relatively short duration noise. The degree of impairment is influenced mainly by the intensity of the noise. The hearing loss can be temporary, lasting from a few seconds to a few days, or permanent. Temporary hearing loss may be caused by relatively short exposure to very loud sound. Impact of noise on hearing Within the inner ear, hair-like cells convert the physical pulse of sound in the air to electrical signals that are sent to the brain. With loud sound, the hair-like cells in the inner ear are pushed over and take time to recover and stand upright again. When the hair-like cells are pushed over, hearing performance is reduced and, in some people, this also causes a ringing sound called tinnitus. With additional exposure, the extent of recovery gradually decreases, and hearing loss becomes permanent. Thus, regular exposure to high levels of noise over a long period may permanently damage the hair-like cells in the cochlea, leading to irreversible hearing impairment. Typical workplace health and safety regulations state that an employer must assess the risk to employees’ hearing, tell the employees about the risks provide employees with personal ear protection devices and explain their use. 2023-01-12 B-09 Human Factors Page 60 of 340 CASA Part 66 - Training Materials Only  For especially loud areas, employers must do all that is possible to reduce exposure to the noise and mark zones where noise reaches a dangerous level and post signs to restrict entry. Efforts should be made to exclude people from noisy areas as much as possible by means of physical barriers with specific signage. Other work areas must also be isolated from the severe noise. Presbycusis Hearing deteriorates naturally as one grows older. This is known as presbycusis. It affects the ability to hear high-pitched sounds first and may occur gradually from age 30 onwards. When this natural decline is exacerbated by noise-induced hearing loss, it can obviously occur rather sooner. Cochlea.org Hearing is impacted by age 2023-01-12 B-09 Human Factors Page 61 of 340 CASA Part 66 - Training Materials Only  Hearing Protection Hearing protection is available, to a certain extent, by using ear plugs or earmuffs. Noise levels can be reduced (attenuated) by up to 20 dB using ear plugs and 40 dB using earmuffs. However, using ear protection will tend to interfere with verbal communication. Despite this pitfall, it must be used consistently and as instructed to be effective. It is good practice to reduce noise levels at the source or move the noise away from workers. Often this