ATPL
Human
Performance
ATPL Human Performance and Limitations ii 27 November 2003
© Atlantic Flight Training
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CHAPTER 1
Introduction to Human Factors
Introduction ...1-1 Accidents and Incidents ...1-2 Public Transport Accident Data...1-2 The Meaning of Human Factors...1-3 A Conceptual Model of Human Factors – The SHEL Model ...1-4 Human Error ...1-6 Pilot Error ...1-7 James Reason Model ...1-7 Confidential Human Factors Incident Reporting Programme (CHIRP) ...1-8 Study and Sleep...1-9 Learning Styles ...1-9 Lecture and Revision Notes ...1-9 Review of Notes...1-10 Methods of Learning ...1-10 Revision Style ...1-11 Revision Method ...1-11 Relaxation ...1-12 Sleep...1-12 CHAPTER 2
Aviation Medicine - Respiration and Circulation
The Atmosphere ...2-1 Measurement of Atmospheric Pressure...2-2 The Standard Atmosphere ...2-2 Standard Atmosphere Pressures and Temperatures for Different Altitudes ...2-2 Physical Divisions of the Atmosphere ...2-2 Gas Laws ...2-4 The Human Need for Oxygen ...2-5 Respiration...2-6 Inspiration and Expiration...2-7 Gaseous Exchange...2-7 Control of Breathing ...2-8 The Circulatory System...2-9 Composition of the Blood ...2-11 Blood Circulation...2-12 Further Uses of Blood Circulation ...2-13
CHAPTER 3
Aviation Medicine - The Effects Of Altitude
Introduction ...3-1 Tracheal air ...3-1 Alveolar Air...3-1 Forms of Hypoxia...3-3 Oxygen Requirements ...3-3 Alveolar Partial Pressure...3-3 Summary of Oxygen Requirements ...3-4 Hypoxia ...3-4 Signs and Symptoms of Hypoxia ...3-5 Stages of Hypoxia...3-6 Susceptibility to Hypoxia ...3-6 Time of Useful Consciousness...3-7
ATPL Human Performance and Limitations iv 27 November 2003
Limitations of Time at Altitude ...3-7 Hyperventilation ...3-8 Symptoms of Hyperventilation ...3-8 Treatment of Hypoxia and Hyperventilation ...3-8 Cabin Decompression...3-9 Climb and Descent...3-10 Climb...3-10 Decompression Sickness...3-10 Re-exposure ...3-11 Treatment of Decompression Sickness...3-12 Flying and Diving ...3-12 Descent...3-12 Sinuses ...3-12 The Ear ...3-13 Prevention...3-14
CHAPTER 4
Aviation Medicine – Health and Hygiene
Introduction ...4-1 Joint Aviation Requirements ...4-1 JAR-FCL and ICAO Annex 1 ...4-1 Medical Fitness ...4-1 Fitness ...4-1 Requirement for Medical Certificate...4-2 Aeromedical Disposition...4-2 Decrease in Medical Fitness ...4-2 Fitness to Fly...4-3 Blood Pressure ...4-3 Hypertension...4-5 Orthostatic Hypotension...4-5 Causes of Orthostatic Hypotension...4-5 Coronary Heart Disease...4-6 Atherosclerosis ...4-6 Risk Factors of Coronary Heart Disease...4-7 Reducing the Risk of Coronary Heart Disease...4-7 Detection and Treatment of CHD...4-8 Stroke ...4-8 Anaemia...4-8 Obesity...4-8 Body Mass Index ...4-9 Effects of Obesity...4-9 Exercise ...4-10 Hypoglycaemia ...4-10 Tropical Diseases ...4-11 Water ...4-11 Food...4-12 Diarrhoea ...4-12 Cholera ...4-12 Amoebic Dysentery, Amoebiasis ...4-12 Diseases Transmitted by Insects ...4-12 Insects and Insect vectors...4-12 Mosquito-Borne diseases...4-13 Malaria ...4-13 Diseases Transmitted by Flies ...4-13 Other Insects...4-13 Hepatitis ...4-14 Immunisations...4-14 Rabies...4-14 Tobacco and Smoking ...4-14
Carbon Monoxide...4-15 Nicotine ...4-15 Drugs and Medication ...4-16 General Health...4-16 Drugs ...4-16 Allergic Reactions ...4-16 Idiosyncrasies ...4-17 Synergistic Effects ...4-17 Effect of Drug Combinations ...4-17 Alcohol ...4-18 Unit of Alcohol...4-18 JAR-OPS 1.115 - Alcohol and Drugs ...4-19 Recommended Amounts of Alcohol...4-19 Alcoholism...4-19 Physical Problems ...4-20 Alcohol and Sleep ...4-20 Toxic Materials...4-20 Toxicology...4-20 Aviation Gasoline (AVGAS) ...4-21 JP4-JP5 ...4-21 Ethylene Glycol ...4-21 Methyl Alcohol...4-21 Chlorobromo Methane (CBM) ...4-21 Halon ...4-21 Hydraulic Fluid ...4-21 Plastics...4-21 Mercury ...4-22 Incapacitation...4-22 Fits and Faints ...4-22 Epilepsy ...4-22 Faint...4-23 Gastroenteritis...4-23 Acceleration ...4-23 Short Term Acceleration ...4-23 Long Term Acceleration ...4-24 Motion Sickness...4-24
CHAPTER 5
Aviation Medicine - Diet and Digestion
Introduction ...5-1 Carbohydrates and Fats...5-1 Fats...5-2 Proteins...5-2 Diet ...5-2 Mineral Salts and Vitamins...5-3 Mineral Salts ...5-3 Vitamins ...5-4 Trace Elements...5-5 Digestion ...5-5 The Alimentary Canal ...5-5 Mouth...5-5 Teeth...5-5 Salivary Glands...5-6 Digestion in the Mouth ...5-6 Pharynx and Oesophagus...5-6 Swallowing ...5-7 Stomach...5-7 Digestion in the Stomach ...5-7 Small Intestine ...5-8
ATPL Human Performance and Limitations vi 27 November 2003
Digestion in the Small Intestine...5-8 Large Intestine ...5-8 Functions of the Large Intestine...5-9 Defaecation...5-9
CHAPTER 6
Aviation Medicine - Metabolism, Excretion And Heat Regulation
The Liver ...6-1 Functions of the Liver...6-1 Pancreas...6-1 Insulin ...6-1 Excretion and Regulation of Body Fluids ...6-2 Functions of the Skin ...6-2 The Kidneys ...6-2 Functions of the Kidneys...6-3 Micturation ...6-3 Body Heat Regulation ...6-3 Heat Production ...6-3 Heat Loss...6-3 Fever...6-4 Heat Stroke ...6-4 Climate and Heat Loss...6-4
CHAPTER 7
Aviation Medicine - The Eye
Introduction ...7-1 Anatomy and Physiology of the Eye ...7-1 Visual Acuity ...7-2 Clarity of Vision ...7-3 Depth Perception ...7-3 Distance Estimation and Depth Perception...7-4 Stereoscopic Vision ...7-4 Monocular Cues...7-4 Geometric Perspective...7-5 Motion Parallax ...7-5 Retinal Image Size...7-5 Known Size of Objects...7-5 Increasing or Decreasing Size of Objects ...7-6 Terrestrial Association ...7-6 Terrestrial Distance of Objects Used to Determine Distance ...7-7 Overlapping Contours or Interposition of Objects ...7-7 Aerial Perspective ...7-8 Emmetropia...7-8 Myopia (Short Sightedness)...7-8 Hypermetropia (Long Sightedness) ...7-9 Presbyopia ...7-9 Astigmatism ...7-9 Spectacles ...7-9 Contact Lenses ...7-9 Radial Keratotomy ...7-10 Colour Vision and Colour Blindness...7-10 Night Vision...7-11 Saccadic Eye Movement...7-12 Sunlight and its Effect on the Eyes ...7-12 Empty Field Myopia ...7-12 Glare ...7-12 Sunglasses ...7-13
Flickering Light...7-13 CHAPTER 8
Aviation Medicine – Visual Illusions
Introduction ...8-1 Spatial Orientation ...8-1 Spatial Disorientation ...8-3 Landing ...8-4 Width of Runway...8-4 Approach...8-6 Runway Gradient and Terrain ...8-7 Runway Slopes Up ...8-7 Runway Slopes Down...8-7 Ground Sloping Down to the Runway ...8-8 Ground Sloping Up to the Runway...8-8 Visual Illusions in the Air ...8-8 Lean on Cloud...8-8 Lean on Sun...8-9 Black Hole Effect...8-10 Visual Factors at Night ...8-11 Reaction Time...8-11 Visual Acuity ...8-12 Blind Spot...8-12
CHAPTER 9
Aviation Medicine - The Ear - Hearing and the Vestibular System
Introduction ...9-1 Noise...9-2 Effects of Noise...9-3 Conductive Deafness...9-3 Cochlea...9-3 Noise Induced Hearing Loss (NIHL) ...9-4 Protection Against Noise...9-4 Presbycusis...9-4 Vibration...9-4 The Vestibular System ...9-4 Semi-Circular Canals ...9-5 Otoliths...9-6
CHAPTER 10
Aviation Medicine – Vestibular Illusions
Illusions of Vestibular Origin...10-1 The Leans ...10-1 Somatogravic Illusion...10-2 The Somatogravic Illusion in Yaw and Roll ...10-2 Somatogravic Illusion in Pitch ...10-4 G-Excess Illusion ...10-6 The Oculogravic Illusion...10-6 Elevator Illusions...10-7 False Perception of Angular Motion – Vertigo...10-8 Somatogyral Illusion...10-8 Oculogyral Illusions...10-9 Illusions due to Cross-Coupled (Coriolis) Canal Stimulation ...10-9 Pressure Vertigo ...10-10
ATPL Human Performance and Limitations viii 27 November 2003
Summary of Disorientation...10-10 Prevention...10-10 Practical Advice to Flight Crew ...10-11 Practical Advice on how to Cope with Spatial Disorientation when it Occurs...10-12
CHAPTER 11
Aviation Medicine – High Altitude Environment
Radiation...11-1 Risk to Flight Crew...11-2 Ozone ...11-2 Humidity ...11-2 Water Vapour...11-2 Relative Humidity ...11-2 Humidity Control ...11-3 Pressurisation ...11-3 Pressurised Cabins...11-3 Cabin Pressurisation Advantages ...11-3 Disadvantages of Pressurised Cabins ...11-4 Aircraft Oxygen Systems...11-4 All Aeroplanes on High Altitude Flights ...11-4 Oxygen Regulator ...11-5 Oxygen masks ...11-5
CHAPTER 12
Sleep
Introduction ...12-1 The Danger of Fatigue ...12-1 Vigilance Effects ...12-1 Causes of Pilot Fatigue ...12-2 Symptoms of Pilot Fatigue ...12-2 Sleep and Sleep Deprivation...12-2 Sleep Credit/Deficit ...12-4 Sleep...12-6 Sleep Disorders ...12-7 Sleep Loss and Microsleep ...12-7 Insomnia ...12-7 Sleepwalking and Sleeptalking ...12-8 Sleep Apnoea ...12-8 Narcolepsy ...12-8 Sleep Hygiene...12-8 Napping...12-9 Drugs ...12-9 Sleeping Tablets ...12-9 Melatonin ...12-9 Circadian Dysrhythmia – Jet Lag ...12-9
CHAPTER 13 Stress Introduction ...13-1 Stress...13-1 Effects of Stress...13-2 Stress is Cumulative ...13-2 Psychological Stressors ...13-4 Effects of Stress...13-6
Physical and Psychological Stress Reactions...13-7 Physical Stress Reactions...13-7 General Adaptation Syndrome...13-7 Psychological Stress Reactions ...13-8 Domestic Stress...13-8 Clinical Effects of Stress ...13-8 Coping Skills ...13-9 Stress Management...13-10
CHAPTER 14
The Nervous System
Introduction ...14-1 The Central Nervous System ...14-1 Brain ...14-2 Spinal Cord ...14-2 The Peripheral Nervous System ...14-3 Sensory Nerves ...14-3 Motor Nerves ...14-3 Autonomic Nervous System...14-3
CHAPTER 15
Human Information Processing
Introduction ...15-1 Sense...15-1 Perception...15-2 Confirmation Bias...15-3 Central Decision Making and Response Selection ...15-3 Ultra-short Term Memory ...15-4 Cocktail Party Effect...15-4 Working Memory or Short Term Memory...15-4 Short Term Memory and its Limitations...15-5 Environment Capture ...15-6 Long Term Memory and its Limitations ...15-6 Motor Memory...15-7 Action Slip ...15-8 Response Execution ...15-9 Attention...15-9 Selective Attention ...15-10 Divided Attention...15-10 Stress and Attention...15-10 Response Behaviour...15-10 Skill Based Behaviour ...15-10 Rule Based Behaviour ...15-11 Knowledge Based Behaviour ...15-11 Feedback ...15-11
CHAPTER 16
Situational Awareness and Attention
Introduction ...16-1 Situational Awareness ...16-1 Building Situational Awareness...16-1 Personal Factors Affecting Situational Awareness...16-3 Three levels of Situational Awareness ...16-3 Situational Awareness Level 1: Monitoring ...16-3
ATPL Human Performance and Limitations x 27 November 2003
Situational Awareness Level 2: Evaluating ...16-4 Situational Awareness Level 3: Anticipating...16-4 Pilot Considerations ...16-4 Briefing/Debriefing ...16-4 Conflict Resolution ...16-5 CHAPTER 17 Communication Communication ...17-1 Effective Communication ...17-1 The Cost of Effectiveness ...17-2 Results of Poor Communication...17-2 The good transmitter...17-2 The good receiver ...17-2 Types of Communication ...17-3 Written Communication...17-3 Visual and Pictorial Ambiguity...17-3 Verbal Communication...17-4 Social Skills...17-4 Body Language...17-4 Verbal Behaviour ...17-5 Listening...17-5 Non-verbal Response ...17-7 Verbal Response ...17-8 Closed Question ...17-8 Open Question...17-8 Leading Question...17-8 Limiting Question ...17-9 Understanding...17-9 Active Listening...17-9 The art of effective listening ...17-9 Status, Role and Ability...17-10 Status...17-10 Role ...17-10 Ability ...17-10 Atmosphere...17-10 Communication summary ...17-11 CHAPTER 18
Personality and Behaviour
Introduction ...18-1 Working Relationships ...18-1 Intelligence...18-2 Personality ...18-2 Assessment ...18-3 Behaviour...18-3 Self Opinion ...18-4 Defence Mechanisms ...18-4 Denial...18-4 Introversion and Extroversion ...18-4 Behavioural Styles ...18-5 Assertive Behaviour ...18-5 Case For Assertiveness ...18-8 Body Language...18-8 Aggressive ...18-8 Non-Assertive ...18-8 Assertive ...18-9
Assertive Behaviour ...18-9 CHAPTER 19 Leadership / Followership Introduction ...19-1 Leadership Qualities ...19-1 Leadership Skills...19-1 The Person Goal (P/G) Model...19-2 Leadership - The Leader...19-4 Qualities Approach...19-4 Situations Approach...19-5 Effective Leadership ...19-5 Attitudes to Leadership ...19-6 Ineffective Leadership...19-7 CHAPTER 20 Decision Making
Decision Making Process...20-1 Reaction to Decision Making...20-1 Making and Taking Decisions ...20-1 Decision Making Models ...20-2 Group Versus Individual Decision Making...20-3 Influences on Decision Making ...20-4 Summary...20-5
CHAPTER 21
Error and Error Chains
Introduction ...21-1 Levels of Human Error ...21-2 Correction of Human Error ...21-2 Group Attitudes ...21-3 SHEL Model Interfaces ...21-3 Links of the Error Chain ...21-4 Breaking the “Error Chain” ...21-5
CHAPTER 22
Learning and Learning Styles
Introduction ...22-1 The Learning Cycle...22-1 Honey and Mumford ...22-3 Flexible Learning...22-4 Maslow...22-4
CHAPTER 23
Automation
Introduction ...23-1 Flight Crew Functions ...23-2 Human Factors Concepts in Design ...23-3
ATPL Human Performance and Limitations xii 27 November 2003
Common Problems with Automation...23-3 Industry Requirements ...23-4 Flight Crew Responsibilities ...23-4 Automation Summary ...23-5 CHAPTER 24 CRM & MCC Introduction ...24-1 What is CRM?...24-2 Why CRM training?...24-2 CRM Loop...24-3 Multi-crew Co-operation (MCC) ...24-3
Chapter 1.
Introduction to Human Factors
“Errare humanum est”
IntroductionFlight safety is one of the major objectives of the ICAO and considerable progress has been made in the past few years. However, additional improvements are needed as it has long been known that approximately 75% of accidents result from less than optimum human performance. This indicates that any advance in the field of Human Performance will have a significant impact on the improvement of flight safety.
This was recognized by the ICAO Assembly which adopted a resolution on "Flight Safety and Human Factors" in 1986. As a follow up to the Assembly Resolution, the Air Navigation Commission formulated the following objective for the task:
"To improve safety in aviation by making States more aware and responsive to the importance of human factors in civil aviation operations through the provision of practical human factors material and measures developed on the basis of experience in States"
Human behaviour and performance are cited as factors in the majority of aircraft accidents. To decrease accident rates, Human Factors in aviation must be better understood and the knowledge more broadly applied. The improvement of awareness in Human Factors presents the international aviation community with the single most significant opportunity to make aviation safer.
To introduce you to Human Performance and Limitations this chapter includes: ¾ A possible meaning and definition of Human Factors
¾ A conceptual model of Human Factors ¾ The industry need for Human Factors
¾ The application of Human Factors in flight operations
¾ The levels of expertise required for flight safety in modern day operations
The human animal has only been flying since the early 1900's. In the quest for more safety in aviation, attention has been focused on the obvious deficiencies of man and machine. Since the early beginnings of flight, great technological advances have been made making aircraft much safer. But what about the human? Has he been forgotten?
This subject deals with the Human Factors that are considered the most important in aviation. The information given should help in the understanding of the human animal and, hopefully, help make aviation safer.
ATPL Human Performance and Limitations 1-2 27 November 2003
Accidents and Incidents
Human error is, by far, the most extensive cause of accidents and incidents in what is now a technologically complex area. Some of the latest accident statistics show that 65% of all accidents in Public Transport aviation have been attributed to flight crew error. It also indicates that for the approach and landing phase of flight, which accounts for 6% of total flight exposure time and 49% of all accidents, flight crew error is cited in 70% as a casual factor.
Public Transport Accident Data
Note: Loading, Taxi and unload are allocated 2% of the flight time. No accidents
are reported in this phase.
Studies have shown that pilot disregard of rules is the most common cause of approach and landing accidents, other causes cited are:
¾ Omission of an action/inappropriate action by a flight crew member eg descent below DH/MDH without the appropriate visual reference
¾ Lack of positional awareness of height above terrain
¾ "Press-on-itis", a decision to continue the approach when conditions are not suitable
The industry need for Human Factors is based on the interaction between the following: ¾ Effectiveness of the system
¾ Safety ¾ Efficiency Take Off Percentage of Accidents 14.4% Percentag e of Flight Time 1% Initial Climb Percentage of Accidents 10.4% Percentag e of Flight Time Climb Percentage of Accidents 6.9% Percenta ge of Flight Time Cruise Percentage of Accidents 4.4% Percentag e of Flight Time Initial Descent Percentage of Accidents 7.2% Percentag e of Flight Time Initial Approach Percentage of Accidents 11.3% Percentag e of Flight Time Final Approach Percentage of Accidents 24.2% Percentag e of Flight Time Initial Landing Percentage of Accidents 19.2% Percentag e of Flight Time 1%
¾ Well being of crew members
Almost everyone involved in Public Transport aviation, from the design of an aircraft to its operation, is concerned with the human element; all need some basic Human Factors training. An Airline will continuously publish bulletins on technical subjects that are likely to be effective because both flight crew and technical personnel realise the importance to the safety of the operation. A similar bulletin on Human Factors topics is unlikely to generate the same response and comprehension unless training is given to the importance of the subject. All airline staff should be exposed to a general level of Human Factors education. Better education means that the Human Element becomes more aware of human performance capabilities and limitations.
Studies indicate that if all sources are included in aircraft accident statistics then 80 - 90% are attributable to human error in one form or another
The Meaning of Human Factors
The human element in aviation can be considered in asset terms as: ¾ The most reliable
¾ The most adaptable ¾ The most valuable
Unfortunately, the pilot is also the most vulnerable to outside influences that can adversely affect performance.
Human Factors is not a single discipline, it draws information from all of the following areas:
Psychology The science of mind and behaviour
Engineering Applying the properties of matter and the sources of energy in nature to the uses of man
Human Physiology Deals with the processes, activities and phenomena characteristic of living matter, particularly appropriate to
healthy or normal functioning
Medicine The science and art of preventing, alleviating or curing disease and injuries
Sociology The study of the development, structure and function of human groups
Anthropometry Study of human body sizes and muscle strength
The above is not a comprehensive list, other disciplines engaged in Human Factors activities include:
¾ Education ¾ Physics
ATPL Human Performance and Limitations 1-4 27 November 2003 ¾ Biochemistry
¾ Mathematics ¾ Biology
¾ Industrial design and operational research
A Conceptual Model of Human Factors – The SHEL Model
It is helpful to use models to aid in the understanding of Human Factors; this allows a gradual approach in the understanding of all factors. The SHEL concept is one such model (Edwards 1972) that lends itself to the aviation environment. The name is derived from the initial letters of the model Software, Hardware, Environment and Liveware. The idea of the model is to establish the concept of a man/machine - environment.
For a basic understanding of the SHEL model consider a football game. Start with the central
L, and then look at the match between interfaces:
L Your team, (Players, Coach, Trainer)
L - L Opposing team (Players, Coach, Trainer), Referee
L - H Ball, Playing surface, Goal
L - E Stadium, Fans, Weather
L - S Rules, Scoreboard, Match importance
The interfaces are not straight edged. Remember that a perfect match is never achievable in real life – is there a perfect football team that never loses?
L
L
S
E
H
L Liveware
H Hardware
E Environment
S Software
L - Liveware - The person - The pilot
To understand the person we need to look at the basic human characteristics:
Physical Size and Shape Design of workspace from anthropometric data (Anthropometry).
Physical Needs The requirement for nourishment
(Physiology and Biology).
Input Characteristics The sensory systems that collect information for the brain
(Physiology, Psychology and Biology).
Information Processing The limitations of human capability (Psychology).
Output Characteristics Once information is processed, the way the human sends messages to the muscles to initiate responses
(Psychology, Physiology and Biomechanics).
Environmental Tolerance The body's capability to withstand temperature,
pressure and humidity
(Physiology, Psychology and Biology).
The liveware (Pilot) is the hub of the SHEL model. The rest of the model must be adapted and matched to this central component.
Liveware – Hardware Cockpit design – will there ever be a perfect flight deck? This
interface is the area considered when an aircraft is designed - yet why does the pilot still have problems with the layout and use of equipment
On the BAC 1-11 flap/gear levers next to each other so that inadvertent operation became a common occurrence.
Liveware – Software The non-physical aspects of a system - procedures, manuals
or checklists etc. Do you keep your aviation documentation up to date?
A Constellation on approach to Prestwick. An experienced pilot flying a radar to visual pattern. The maps on the aircraft showed masts, on the approach, up to 50 ft agl - in fact they were up to 500 ft agl. The aircraft crashed, hitting the masts, killing all persons on board.
Liveware – Environment Errors associated with the environment - noise, heat, lighting and vibration. The earliest interface to be recognised in flying. The challenges of pressurisation, air conditioning, vibration and sound proofing have been
ATPL Human Performance and Limitations 1-6 27 November 2003 understood and dealt with in most modern aircraft. New challenges such as the problems associated with sleep disturbance are now the major causes of concern.
Liveware – Liveware The interface between people. Poor interaction means poor
crew effectiveness. This relates to all aspects of an airline operation. Any person dealing with a flight must be considered in this area. Flight crew human factors training attempts to minimise the mismatches that occur with this interface.
Human Error
Mismatches occur with the interfaces of the SHEL model as no human is perfect. Even though aircraft have developed technologically over the last 50 years the human being has not evolved at the same rate. New equipment can surpass the human capability to effectively operate it. All humans make mistakes - All pilots make mistakes. But remember, not all mistakes lead to disasters. The simple error model below illustrates the effect a pilot can have on a flight:
PILOT ⇒ ERRORn⇒ DISASTER
Where ERRORn is a sequence of more than one error.
The F28 accident at Dryden, Ontario, in March 1989 is a good example of how this model works. On the face of it, this was a clear cut case of pilot error. The immediate cause of the crash was the failure of the flight crew to obtain adequate protection against wing icing prior to departure. The inquiry yielded a 6 volume report; probably the most exhaustive air accident report ever. The conclusion:
“The accident was not the result of one cause but of a combination of several related factors. Had the system operated effectively, each of the factors might have been identified and corrected before it took on significance. This accident
was the result of a failure in the air transportation system as a whole.”
Each sequence of this model needs to be attacked.
PILOT ⇒ ERRORn
Remedy
¾ Training - manuals, simulator training. ¾ Cross monitoring, 2 pilot operation. ¾ Crew fatigue and stress.
ERRORn ⇒ DISASTER
Remedy
¾ Cockpit/aircraft design.
Pilot Error
The phrase Pilot Error is peculiar to aviation; there is no equivalent in the civilian world - Doctor Error, Engineer Error etc. The phrase is “falling from grace” especially with the advent of better Human Factors training. However, there is a need to evaluate the human response to the above error progression. Crew Resource Management (CRM), Multi-Crew Co-operation (MCC) and Human Factors training all play a role in ensuring the safety of the aircraft, crew and passengers. CRM and MCC are discussed in a later chapter.
In aviation terminology an "incident" is a dangerous event but with no serious consequences. According to Frank Bird, for every fatal accident there are 600 incidents with no accident potential.
The conventional way to represent the role of Human Factors in accidents is to count each accident where there was clear human error involvement. Looking at fatal accidents, if we list the human factors contributions to these fatalities, the top 4 causes are:
Controlled flight into terrain (CFIT) 2169 Maintenance and inspection 1481
ATC and Comms 1000
Approach and Landing without CFIT 910
To further explain the error model the James Reason Swiss Cheese Model is used.
James Reason Model
To explain the Frank Bird model we can break down the above diagram into a what is termed the Swiss Cheese Model. Aviation can be broken into two failure areas:
1
10
30
600
Disabling Injury – Fatal Accident
Minor Injury – Accident/Incident
Property Damage – Incident
ATPL Human Performance and Limitations 1-8 27 November 2003
Active Failures Errors and violations by the human element – the pilot
Latent Conditions Resident pathogens that may lie under the surface for years
We cannot prevent the latent conditions, we can only make them visible to those who manage and operate the system. All decisions, even the good ones, will have a downside for someone, somewhere in the system. The resident pathogens are more difficult and this is where the model, shown below, is important.
The resident pathogens may lie dormant for years. All pilots make errors. Put this with the immediate mental precursors of an error - distraction, preoccupation, forgetfulness --then the sequence of the Error model is being put into place. All that is needed is for the resident pathogens to occur together (Errorn). Then the holes in each part of the model line up and the
accident will occur (Sequence a). Where the errors occur and the holes are not matched then the sequencing will stop - and no accident will occur (Sequence b).
Confidential Human Factors Incident Reporting Programme (CHIRP)
A totally confidential reporting system about Human Factors incidents that do not get reported. CHIRP is a charitable company run from RAE Farnborough. Similar schemes are run on behalf of the national Civil Aviation Authorities throughout the world. CHIRP is outside the control of the CAA. Feedback, a 3 monthly magazine, is produced that covers a wide range of Human Factors topics such as:
¾ Sleep and Fatigue ¾ Stress
¾ Communication ¾ Operating difficulties ¾ Technological problems
This system relies on the honest reporting of any incident or occurrence. Flight Crew, Cabin Crew, Engineers and ATC controllers can make reports. For Example:
Manufacture
Accident Acceptance into Airline Service Design and development
Sequence b Sequence a Development of technical servicing procedures Implementation of SOP's
I had two early mornings on two consecutive days to do two European flights and I was rostered for a night standby the following day at 0830L and did not sleep again that day. At 1900L crewing phoned to call me in for a UK - Europe - UK on which the crew were already into discretion.
All went according to plan and I still felt fine as we set off from Europe for the UK (0300L). Due to the overlap of duty times we had three pilots on the flight deck and as always there was more stimulation and conversation than usual and I didn't start to feel jaded until the last 90 minutes of flight. With one hour to go I really started to feel tired but thought I should be able to last the flight without falling asleep. At the top of descent my eyes closed for the first time and I was in somewhat of a dozy state during the descent. I still felt, however, that I could make a big final effort during the last 10 minutes of the flight when there was more activity. Going downwind for landing, the approach checks, RT calls and then the flap setting did increase the activity but I simply felt worse than ever. Commands/actions were followed immediately by falling asleep again. On final approach I found myself being woken up as the Captain was asking for gear down, flaps etc. When we finally landed I felt dreadful and possibly the worst in many years of flying.
There are obvious safety implications from this incident not the least of which was my driving home (0830L) afterwards. The irony of the situation was that the two pilots in discretion had been accommodated by crewing and felt fine whereas I was still within my allowed FDP and felt like death. I think that standby duties during late evening/early morning are almost impossible to rest and prepare for properly but can be acceptable with good rostering. I swear I will never accept an early morning duty followed by late evening standby on the roster again. Study and Sleep
Learning Styles
Learning "Parrot Fashion" was once the only form of learning in most schools. Nowadays, this system has changed to one where the student is expected to learn, understand and apply the material taught. This is no different in ab-initio pilot training, you will be presented with copious amounts of material to help you pass your groundschool exams. But what is essential to pass the exams?
Lecture and Revision Notes
The following is written for a full time student but the revision techniques apply to all. However, the means of study and revision note taking apply to Distance Learning. Students have to develop a method of copying the information that a lecturer is trying to pass on. This is usually done by note taking. Taking notes does help people remember what was said, and taught, in lectures. To ensure that notes are effective takes practice; it is not an easily acquired skill. The initial difficulty any student has is to decide what to write down. A student cannot write down everything that is said; how do you sift out the wheat from the chaff? This chapter is designed to help a student make notes of value such that revision is made easier.
ATPL Human Performance and Limitations 1-10 27 November 2003 One good way to start is to sort out what has to be learnt into:
M - What I must Memorise
U - What I must Understand
D - What I must be able to Do
Common Problems
¾ The student has no control over how fast the lecturer delivers the lesson.
¾ How much material does the student need to write down; in note taking, more is not necessarily better.
¾ Too much detail means little time is spare for thinking about what is being taught. Taking detailed, accurate notes, requires the student to pay attention to everything that is said. Therefore, the time that a student needs to think about what notes to take is as important as the time that attention is paid to what the lecturer is saying. Remember, borrowing notes is never as effective as writing the notes during a lecture. The starting point for any note taking must be the building of an effective framework from which to work.
Note Framework:
Subject Heading. The lecturer will always write or state the lesson
objective. This must be the starting point.
Sub Heading. The lecture will be split up into minor topics each with its own
explanations.
Calculations. Any calculation made by a lecturer must be included. Ensure
that you copy all calculations exactly as they have been written on the board.
Review of Notes
Notes should be made by making connections with all the related material (MUD). It is important to review any notes as soon as possible after they have been taken. If this review is done at an early stage it is possible to relate them to text book material. Remember, the notes have to be used at a later date for revision.
Methods of Learning
As examinations approach, the student needs to be able to recall and use the information that has been taught.
¾ No allowance is made for difficult sections of text.
¾ If a portion of text is not understood, then the student ignores it. ¾ Text is skipped over, not read comprehensively.
Revision Style
Successful students monitor their performance. ¾ A study plan is made and followed.
¾ Difficult sections are re-read till understood. ¾ Periodic reviews are made of the material Effective learners need to:
¾ Understand the material that has been taught.
¾ They must be able to relate the facts learnt to other course material.
¾ They must be able to organise this material into easily remembered, and easily accessible, facts.
Revision Method
To help with revision the SQ3R method can be used. This method of revision is a successful way for remembering textbook material. The SQ3R way of learning is:
SURVEY Do not begin by reading the material. Look at the subject headings, bold type headings or italic terms. Obtain an idea of how much material is to be learnt or discussed. Decide on how to split the text into easily learnt packages.
QUESTION Before reading each section ask yourself questions about what is to be learnt.
READ Read the text. Think about the material as it is read. Ask questions of understanding and complete calculations if necessary. If text is not understood - DO
NOT PROCEED. Ask for help at this stage, from other course members or staff
members. Make sure all the material is understood before progressing to the next part of the revision package.
RECITE At the end of each major section recite the major points to yourself. Do not skip over any areas. As you become more familiar with the information being presented, then the temptation is to miss out large chunks of material that you think you know.
REVIEW The most important section. Review all the material learnt by using reciting or questioning techniques. Using other course members, in question and answer sessions, helps to reinforce all the material learnt.
ATPL Human Performance and Limitations 1-12 27 November 2003
Relaxation
Make sure that you take breaks during the learning process. Revision can be tedious, especially if there is a lot of text to be learnt. Short breaks every hour make sure that you stay refreshed during the toil. Do not revise one subject a night, this will lead to boredom; aim to revise 2 or more subjects.
Sleep
Individuals require differing amounts of sleep. The older you are the less sleep you require. However, people in learning situations do require regular sleep patterns. An integrated flying course requires a student to both fly and carry out an intensive ground school phase. Pressures are such that students start to disrupt their sleep by late night study or worry. Sleep is covered in more detail during the later stages of HPL, this small section is designed to help make a student comfortable in his new environs.
¾ Make the room comfortable - pictures on walls, personal possessions. These all make an area feel comfortable - more like home.
¾ No strenuous exercise immediately before going to bed. This means no physical or mental exercise.
¾ A high level of study activity should be avoided immediately before trying to sleep.
¾ Ensure that after working there is sufficient time to relax. The brain needs time to wind down.
¾ Keep the room ventilated - not too warm, not too cold.
¾ Do not drink too much alcohol. Alcohol induces a coma like sleep where there is no body refreshment.
¾ Try a warm milky drink - NOT COFFEE or tea.
¾ Light reading or listening to music can help relax the mind and body.
Do not jump into bed, straight after finishing studying, and expect to fall asleep immediately. If you find that you are not sleeping well try to stay in bed where it is warm. There is some suggestion that you will get some relaxation and body revitalisation even whilst lying down. Finally DON'T worry.
Chapter 2.
Aviation Medicine - Respiration and Circulation
The Atmosphere
The Earth is surrounded by a mixture of gases known as the atmosphere which is held in place by the force known as gravity. The mixture of the atmosphere remains constant and is found to cover the earth up to 30 000 ft at the poles and 60 000 ft at the equator. The boundary of the atmosphere is known as the tropopause.
Within the atmosphere there is normally a decline in temperature of approximately 1.98ºC/1000 ft. Pressure also decreases with altitude. Cold temperature increases air density; low pressure decreases air density. Pressure change is the dominant force and as such the air density decreases with altitude. In the atmosphere, small increases in height at low altitude will cause a much greater change in pressure than the same height change at altitude.
30 000 ft 60 000 ft
Outer Space – No Molecules
High Altitude – High Density of Molecules Low Altitude – Very High Density of Molecules
ATPL Human Performance and Limitations 2-2 27 November 2003
Measurement of Atmospheric Pressure
Standard atmospheric pressure, or barometric pressure, is the weight or force exerted by the atmosphere at any given point. This pressure is expressed in different forms by the method of measurement such as pounds per square inch (psi), millimetres of mercury (HG) and inches of mercury. Millimetres of mercury (mm/HG) are used in these notes.
The Standard Atmosphere
Continual fluctuations of temperature and pressure in the atmosphere create problems for engineers and meteorologists who require a fixed standard of reference for aircraft. This standard is known as the International Standard Atmosphere (ISA). Conditions throughout the atmosphere for all latitudes, seasons, and altitudes are averaged and published by ICAO. The resultant standard atmosphere has specified sea level temperature and pressure and specific rates of change of temperature and pressure with height.
Standard Atmosphere Pressures and Temperatures for Different Altitudes:
Sea level 760.0 mm/HG +15°C
10 000 ft 522.6 mm/HG -05°C
18 000 ft 379.4 mm/HG -21°C
33 700 ft 190 mm/HG -52°C
40 000 ft 140.7 mm/HG -56.5°C
Physical Divisions of the Atmosphere
The divisions of the atmosphere are primarily physical or meteorological in nature. From meteorology we are familiar with both the troposphere and the stratosphere; both of which are important to the aviator and aviation. To look at the Physiological Effects associated with flight the atmosphere can be split into four zones:
Physiological Zone This area extends from sea level to approximately 12 000 ft.
It represents the area of the atmosphere to which the human body is more or less adapted. Only minor physiological problems exist when flying within this zone. Pilots who go higher than their acclimatized levels notice common symptoms such as middle ear blockage and sinus blockage difficulties, shortness of breath, dizziness and headache. Above this zone we are in an environment to which our body is unaccustomed.
Physiological Deficient Zone Existing from 12 000 ft to 50 000 ft this zone, along
with the previous zone, is the area in which most flying takes place. Oxygen deficiency becomes an ever increasing problem as we ascend due to the reduced atmospheric pressure.
Partial Space Equivalent Zone This zone extends from 50 000 ft to 120 nm, where pressure changes become very small. The problems for flight over 50 000 ft are the same as those encountered in space. Sealed cabins, pressure suits are
necessary as problems now occur with blood and body fluids boiling over 63 000 ft. Gravitational changes on the body make this a space equivalent zone. Only Concorde has operated in this zone.
Total Space Equivalent Zone True space, this zone extends outwards from 120 nm.
The physiological problems of this zone are similar to the previous zone. The air is composed of a mixture of gases of nearly constant proportions:
Oxygen 20.94% Nitrogen 78.08%
CO2 0.03%
Other gases 1%
These proportions remain the same at all levels within the troposphere and up to an altitude of 60 000 ft. ICAO has defined the standard atmosphere which assumes:
Pressure 1013.2mb
Temperature 15ºC
Density 1225 gm/cubic metre
The temperature lapse rate of 1.98ºC/1000 ft continues up to 36 090 ft. Above this altitude the temperature remains constant at –56.5°C.
Pressure falls 1 hPa per 30 ft gained in the lower levels of the atmosphere (acceptable in the first 5000 ft)
ATPL Human Performance and Limitations 2-4 27 November 2003
Gas Laws
The human body is adapted for life at sea level. If exposed to an altitude of 40 000 ft then a person will become unconscious in a few seconds and dead a few minutes later. Knowledge of the gas laws is essential in explaining the effects of reduced Barometric Pressure on the body.
Boyle’s Law For a fixed mass of gas at constant temperature (T), the pressure (P) is inversely proportional to the volume (V). If the pressure on a gas decreases, its volume increases and vice versa. This law, when applied to the body, explains the expansion of gases trapped within the body in areas such as the middle ear, sinuses and gastro-intestinal tract.
P x V = C
Where: P Pressure
V Volume C Constant.
Charles’s Law If the volume of a gas remains constant, the pressure will vary directly with the temperature.
Algebraically PV = RT or
PV/ T = R
P Absolute pressure V Volume
R Universal gas constant
700 600 500 400 300 200 100 0 0 10 20 30 40 50 60 PRESSURE (mmHg) ALTITUDE (x1000 FEET)
T Temperature
Dalton’s Law In a mixture of gases, the pressure exerted by one of the gases is the
same as it would exert if it alone held the same volume. From this the partial pressure of oxygen in the atmosphere can be derived for any altitude, since the pressure at that altitude can be measured and the proportion of oxygen in the atmospheric air is constant. This is of great importance to aviation especially when we discuss Hypoxia. To determine the partial pressure of each gas in the mixture we use the following:
Ptotal = ppA + ppB + ppC….
Where Ptotal represents the total pressure of the mixtures of gases and ppA, ppB, or ppC
represents the partial pressure of each gas in the mixture.
Graham’s Law A gas of high pressure will exert a force towards a region of lower pressure and if a membrane separating these regions of unequal pressure is permeable or semi-permeable, the gas of higher pressure will pass through the membrane into the region of lower pressure. This will continue until the unequal regions are nearly equal in pressure. This law explains the transfer (diffusion) of oxygen, CO2 and other gases from one part of the body to another.
Henry’s Law The amount of gas in solution varies directly with the pressure of that
gas over the solution. When the pressure of a gas over liquid decreases, the amount of gas dissolved in the liquid will also decrease, or vice versa. This gas law is applicable when Decompression Sickness is discussed when Nitrogen comes out of the blood.
General Gas Law A combination of Boyle’s Law and Charles’s Law where P and T signify absolute pressure and temperature, respectively.
P1V1 = P2V2
T1 T2
The general gas law applies to "ideal" gases where the molecules are assumed to be perfectly elastic. For practical purposes we accept that the law applies to all gases.
The Human Need for Oxygen
To live, the human being must produce heat and energy from food eaten. Eaten food is converted into simple food products and transferred to the tissues by the blood. It is then oxidized to provide this heat and energy. To oxidize the food, oxygen has to be supplied to the living cells in the body. The waste product, carbon dioxide, is then carried away from the tissues and expelled from the body. This process is respiration. The definition of respiration is given below:
ATPL Human Performance and Limitations 2-6 27 November 2003
“The exchange of the respiratory gases, O2 and CO2, between the organism and its
environment.” Respiration
The breathing process consists of two phases:
Breathing In Inspiration
Breathing Out Expiration
The respiratory system is made up of the following: ¾ Mouth and nose
¾ Trachea ¾ Bronchus ¾ Bronchiole tree ¾ Alveoli.
When a human breathes, air is drawn in through the mouth or nose to the Pharynx. The Pharynx, which is found at the back of the throat, warms, humidifies and filters the air before it passes down the trachea into the two bronchi. The bronchi split into the bronchiole tree as the air passes into the lungs. The lungs are set inside the chest cavity, or thoracic cavity, wrapped in an airtight sac called the pleura. At the ends of each branch of the bronchiole tree are air sacs, alveoli. These air sacs are very small and are surrounded by capillaries which are small blood vessels. The thin walls of the alveoli and capillaries allow oxygen to diffuse into the blood and CO2 into the alveoli. The lungs in the average man can hold approximately
6 litres of air, a woman, 4 litres.
Tidal Volume The volume of air breathed in and out in a single breath. When
resting this is approximately 500 cm3
AIR TRACHEA BRONCHUS BRONCHIOLE ALVEOLI CAPILLARY NETWORK GAS EXCHANGE
The maximum volume that can be breathed in and out is approximately:
Men 2500 cm3
Women 1500 cm3
Inspiration and Expiration
The chest cavity is surrounded by the ribs on the sides and separated from the abdominal cavity by the diaphragm, a large flat sheet of muscle. The chest cavity has only one opening. Any change in volume to the chest cavity will ventilate the airspace in the lungs. The chest size is altered by a muscular action that raises and lowers the diaphragm and by contraction and relaxation of the muscles between the ribs.
Inspiration and expiration circulate air in and out of the lungs efficiently.
Gaseous Exchange
The constant turnover of air provides the mechanism for both O2 to diffuse into the blood and
CO2 to diffuse into the lungs.
This gaseous exchange can be explained by looking at the partial pressure each gas exerts. In air outside the lungs the partial pressure of O2 is 160 mmHg. Carbon Dioxide has a low
partial pressure in outside air of approximately 0.3 mmHg. The difference in pressure of these gases between the alveoli and the blood is how the gaseous exchange between the lungs and the bloodstream occurs.
¾ Blood entering the lungs has a lower ppO2 than the alveolar air, so oxygen
diffuses into the blood 1 2 3 4 INSPIRATION 1 RIBS RAISED 2 DIAPHRAGM DEPRESSED 3 LUNGS EXPAND 4 AIR DRAWN IN 5 6 7 8 EXPIRATION 5 RIBS RETURN 6 DIAPHRAGM RELAXES
7 LUNGS RETURN TO ORIGINAL VOLUME 8 AIR EXPELLED
ATPL Human Performance and Limitations 2-8 27 November 2003 ¾ The ppCO2 is higher in the blood entering the lungs than in the alveoli, so CO2
diffuses out of the bloodstream and into the lungs
TRACHEA (WINDPIPE) BRONCHI BROCHIOLES LUNG CO2 O2 CO2 O2 CO2 CO2 O2 O2 PULMONARY ARTERY RESPIRATORY BRONCHIOLE ALVEOLI PULMONARY VEIN DEOXYGENATED BLOOD OXYGENATED BLOOD
Most of the oxygen is taken into the blood, and carried, by the protein haemoglobin. Haemoglobin is found within the red blood cells and is an Iron rich compound. The Haemoglobin bond ensures that the body can receive enough Oxygen for the body’s needs. If blood diffused directly into the blood solution only, then the body would be starved of sufficient Oxygen necessary for the human to survive. Oxygen remains bound to the haemoglobin until it reaches the tissues of the body, an area of low oxygen tension. This oxygen is then released into the tissues to oxidize food. About 95% of the oxygen is transported by haemoglobin, as an oxy-haemoglobin bond, and the remainder is diffused directly into the blood solution. Some Carbon Dioxide binds to the haemoglobin but the majority diffuses into the blood and is carried in solution as carbonic acid. Both Oxygen and Carbon Dioxide bind weakly to the Haemoglobin as a strong bond would result in difficulties in releasing the gases to either the tissues or the lungs.
Control of Breathing
Control of breathing is centred in the respiratory centre of the brain. The human requires no conscious effort to breathe; although the rate of breathing can be altered voluntarily. Inspiration is the active phase of breathing; expiration the passive phase. The rate and depth of breathing can be adjusted to meet any change in the consumption of oxygen and expiration of carbon dioxide.
Under normal conditions the body is slightly alkaline (pH7.4). During respiration:
¾ The acidity level increases
¾ The pH value lowers to less than 7.4
Any increase in the CO2 concentration in the blood stimulates an increase in the ventilation
rate. As blood flows through muscle capillaries the dissociation of oxy-haemoglobin to release oxygen is increased by:
¾ Low O2 concentration in muscle tissue
¾ High CO2 concentration
¾ High temperature
Too little CO2 causes the blood to become more alkaline and the pH value to rise. The human
body maintains the equilibrium within narrow limits, any shift in the blood pH and ppCO2 levels
are sensed by the respiratory centres of the brain. When unusual levels occur, chemical receptors trigger the respiratory process to help return the ppCO2 and pH levels to normal
limits. For the uptake of O2 by the blood and the release of that O2 to tissues the extreme
limits of the pH of the body are regarded to be 7.2 to 7.6.
The brain monitors the levels of both carbon dioxide and oxygen in order to make any changes in the respiration rate.
Note: A healthy body is more sensitive to changes in the carbon dioxide balance of the body than to oxygen.
The Circulatory System
The circulatory system is concerned with the transportation of blood throughout the body. The blood has the following functions:
¾ The carriage of oxygen and the carriage of carbon dioxide ¾ The carriage of food
¾ The carriage of nitrogenous waste
¾ The carriage of hormones or chemical messengers ¾ The protection of the body against disease
¾ Regulation of body temperature
The circulatory system centres on a muscular pump - the heart. The heart is a hollow organ with a wall made of three layers:
The Pericardium The outer layer
The Myocardium The middle layer
ATPL Human Performance and Limitations 2-10 27 November 2003 This heart is made up of four chambers; Two atria which are thin walled, the suction chambers, and two ventricles which are thick walled, the discharge chambers.
The Ventricles The left ventricle, which pumps blood around the body, has a much thicker wall than the right ventricle, which only pumps blood to the lungs
Separation of the Atria and the Ventricles The atria and ventricles are separated by the atrio-ventricular valves:
Tricuspid Valve Separates the right atrium from the right ventricle
Mitral Valve Separates the left atrium from the left ventricle
HEART AND BLOOD FLOW
Right Atrium Two veins enter the right atrium, the inferior vena cava and the
superior vena cava. These veins bring blood back to the heart from all of the body except the lungs. Blood from the right atrium passes into the right ventricle and then into the pulmonary artery to the lungs
Left Atrium Blood from the four pulmonary veins runs into the left atrium. This blood is passed into the left ventricle which is connected to the main artery which passes blood to all parts of the body except the lungs. This main artery is known as the Aorta
The blood is circulated around the body by a network of flexible tubes, the blood vessels
Arteries Strong, muscular and elastic walled vessels, arteries carry mainly oxygenated blood. All arteries flow away from the heart. The exception is the pulmonary artery which carries de-oxygenated blood from the heart to the lung.
Veins Thin walled vessels, with one way valves, veins carry mainly de-oxygenated
blood back to the heart. The exception is the pulmonary vein which carries oxygenated blood from the lungs to the heart.
Capillaries Arteries sub-divide to form a dense network of fine thin-walled blood vessels known as capillaries. The thin capillary walls allow the exchange of gases and other material between the cells of the body and the blood. The capillaries eventually rejoin passing through the tissues to become veins.
Composition of the Blood
Blood is a complex tissue made of different kinds of cells, free proteins, other chemicals and factors and water.
The average adult has about 6 litres of blood circulating in the body. Blood consists of a clear yellow fluid (plasma) and solids. Approximately 90% of the plasma is water, in which other substances are dissolved or suspended. The most important solids in suspension are
Red blood cells The red blood cells are formed in the bone marrow and contain a red pigment, haemoglobin. This is also the protein that carries oxygen to the tissues. Haemoglobin is an iron-containing compound. The iron that is in the haemoglobin molecule is responsible for the chemical affinity of haemoglobin for Oxygen and Carbon Monoxide.
White Blood cells Several kinds of cells found in the blood are colourless or white in appearance. All of these cells play a role in protecting the body from disease. The white blood cells are formed from “stem cells” found in the bone marrow. These cells mature into the specialized forms that protect the body from infection. Although these white cells are located in the blood, they function as part of the body’s immune system.
Platelets Platelets help the blood clot. When a blood vessel is severed or torn the damaged ends constrict and retract in order to minimize blood loss. Almost immediately the blood that is escaping from the damaged vessel begins to clot. Platelets congregate at the site of the injury and release clotting factors. These clotting factors start to convert one of the blood substances, fibrinogen, into the protein, fibrin. Fibrin forms a dense weblike structure that in turn traps more platelets. This forms into a jelly like clot taking about 10 minutes. As the clot hardens it begins to shrink, releasing a watery substance, serum. The serum carries antibodies to combat infection and specialized cells that begin the process of repair.
Together the above cells account for 45% of the blood’s total volume the remainder is called plasma.
Plasma Plasma is a yellow, slightly alkaline fluid consisting of 90% water and 10% solid matter. The composition of the plasma is controlled mainly by the kidneys, these solids include:
ATPL Human Performance and Limitations 2-12 27 November 2003 ¾ Proteins
¾ Amino acids ¾ Fats
¾ Glucose
¾ Urea and other nitrogenous waste ¾ Salts
Blood Circulation
The cycle of blood flow through the body is as follows:
¾ Blood from the right atrium is pumped into the right ventricle
¾ From the right ventricle the blood goes into the pulmonary artery which carries blood to the lungs
¾ In the capillaries of the lungs, gaseous exchange occurs: ¾ Oxygen is taken into the blood
¾ Carbon dioxide is passed into the lungs
¾ The freshly oxygenated blood returns to the left atrium of the heart via the pulmonary veins
¾ The left atrium empties into the left ventricle which is connected to the aorta ¾ Contraction of the left ventricle forces blood into the aorta, the major artery which
is connected to the rest of the body save the lungs
¾ The aorta divides into arteries that carry the blood to the tissues. These arteries divide into capillaries which give off the oxygen and take up carbon dioxide before the blood returns to the heart
¾ All blood returning to the heart collects in the superior or inferior vena cava which feed directly into the right atrium
Further Uses of Blood Circulation
As the blood passes through the body the following organs carry out the following functions:
Stomach Nutrition from food is picked up and carried along to the tissues
Spleen Old blood cells are taken out of circulation
Liver Removes toxins and adds proteins to the blood
Kidneys Adjust the water content and remove waste products
Bone Marrow Helps renew white blood cells HEAD AND ARMS LUNG LUNG LIVER INTESTINE KIDNEYS LEGS AORTA PULMONARY ARTERY PULMONARY VEIN VENAE CAVA E LEFT ATRIUM LEFT VENTRICLE RIGHT ATRIUM RIGHT VENTRICLE
HEPATIC PORTAL VEIN
OXYGENATED BLOOD DEOXYGENATED BLOOD DIRECTION OF BLOOD FLOW
ATPL Human Performance and Limitations 2-14 27 November 2003 Intentionally Left Blank
Chapter 3.
Aviation Medicine - The Effects Of Altitude
Introduction
The atmosphere is a mixture of gases of constant proportions up to an altitude of 60 000 ft. The approximate figures are:
Oxygen 21%
Nitrogen 78%
Other gases 1%
As altitude increases, pressure and density decrease and the amount of Oxygen available to the red blood cells decreases.
Two gases cause further complicating factors:
Water Vapour Ever present in the atmosphere, water vapour content varies depending upon the climatic conditions. In the lungs, the alveolar air is always saturated with water vapour. This accounts for 6% of the volume of air in the lungs at sea level.
Carbon Dioxide The amount of carbon dioxide in the atmosphere is approximately 0.03%. In the lungs, because of the respiration process, the amount of CO2 is higher; equivalent to 5.5% of
the available volume at ground level.
These gases have to be taken into account when considering the amount of Oxygen available to the respiration process. At sea level, because of the amount of water vapour and CO2, the
volume of Oxygen in the lungs available for the respiration process is reduced to 14.5%.
Tracheal air
When inhaled air is drawn into the respiratory passages, it becomes saturated with water vapour and is warmed to body temperature. This water vapour has a constant pressure of 47 mmHg at normal body temperature. This is regardless of the barometric pressure. The inspired gases available for the respiration process are reduced by the amount of water vapour present.
Alveolar Air
The tracheal air enters the lungs and Oxygen and CO2 are exchanged in the respiration
process. The expired air has less Oxygen and more carbon dioxide content. The partial pressure of O2 (ppO2) in the alveoli varies with the CO2 partial pressure. A constant,
ATPL Human Performance and Limitations 3-2 27 November 2003 ventilation rate creates a CO2 partial pressure of approximately 40 mmHg. Using these values
the ppO2 at any altitude can be calculated. Where:
P Ambient barometric pressure in mmHg
F The fractional percentage of the inspired gas
ppH2O(tr) Water vapour partial pressure constant at 47 mmHg at 37oC
ppO2(tr) Tracheal Oxygen partial pressure
ppCO2(alv) Alveolar carbon dioxide partial pressure constant at 40 mmHg with
normal ventilation rate
ppO2(alv) Alveolar Oxygen partial pressure
To calculate tracheal gas:
ppO2(tr) = (P - ppH2O(tr)) x F
In the transition from tracheal air to alveolar air, the ppO2 is reduced and ppCO2 is increased.
We assume that the ppN2 remains constant.
To calculate alveolar gas:
ppO2(alv) = ppO2(tr) - ppCO2(alv)
Example At 10 000 feet the air pressure is 523 mm Hg, using 21% as the percentage O2. What is the alveolar partial pressure of O2?
Step 1 Calculate the tracheal gas:
ppO2(tr) = (P - ppH2O[tr]) x F
ppO2(tr) = (523-47) x 0.21 = 99.96 mm Hg
Step 2 Calculate the alveolar gas:
ppO2(alv) = ppO2(tr) - ppCO2(alv)
ppO2(alv) = 99.96 mm Hg - 40 mm Hg = 60 mm Hg
The calculated alveolar partial pressure of Oxygen in the lungs is 60 mm Hg at 10 000 ft altitude.
A pressure gradient is required to ensure that Oxygen diffuses from the alveoli into the red blood cells. If this pressure gradient falls, Oxygen movement into the blood is impaired. Some degree of protection is given to the body up to 10 000 ft because of the affinity of haemoglobin for Oxygen. The body has a “surplus” of Oxygen for use to this height. Above 10 000 ft the partial pressure of Oxygen in the alveoli falls off rapidly and the over protection is lost. The body begins to suffer from a lack of Oxygen; a process known as Hypoxia.
Forms of Hypoxia
Hypoxic Hypoxia. Caused by an insufficient partial pressure of Oxygen in the inspired air. This reduction of Oxygen becomes apparent above an altitude of 10 000 ft. Most likely in aviation when an aircraft has a decompression.
Anaemic Hypoxia. Anaemic Hypoxia, also known as Hypaemic Hypoxia, is caused by a reduction in the Oxygen carrying capacity of the blood. This reduction can be caused by a lowering in the amount of circulating haemoglobin, Anaemia. Haemoglobin forming a bond with carbon monoxide produces the same result.
Stagnant Hypoxia. Defined as an Oxygen deficiency in the body due to poor blood circulation. Caused by a failure of the circulatory system. When flying, this type of Hypoxia, can be caused by problems such as pressure breathing or excessive "G" forces.
Histotoxic Hypoxia The inability of the body to utilize Oxygen. Caused by a failure of the body tissues to use the available Oxygen efficiently because of impairment to cellular respiration. Poisons such as drugs and alcohol are the usual cause.
Oxygen Requirements
As altitude increases the Oxygen pressure decreases:
¾ By 8000 ft the atmospheric pressure is only ¾ of the sea level pressure ¾ At 18 000 ft the atmospheric pressure is ½ that at sea level
¾ By 33 500 the atmospheric pressure is ¼ of the sea level pressure
As altitude increases, the percentage of Oxygen that needs to be added to the gas a pilot breathes needs to increase to ensure that the alveolar partial pressure is maintained.
Alveolar Partial Pressure:
Sea Level 103 mm Hg
ATPL Human Performance and Limitations 3-4 27 November 2003 Above 10 000 ft extra Oxygen needs to be added. The percentage of Oxygen added increases until 33 700 ft where 100% Oxygen is required to give the equivalent alveolar partial pressure to that at sea level (103 mmHg). Above this height the partial pressure can be allowed to fall to the 10 000 ft equivalent of 61mmHg - this occurs at 40 000 ft. Above 40 000 ft positive pressure breathing, the forcing of Oxygen under pressure into the lungs, is required.
Summary of Oxygen Requirements
HEIGHT OXYGEN REQUIREMENT ALVEOLAR PARTIAL
PRESSURE
0 - 10 000 ft Air only 103 mm Hg
10 000 - 33 700 ft Increasing percentage of Oxygen required 61 mm Hg
As % of 02 increases so the
equivalent partial pressure increases
33 700 - 40 000 ft 100% Oxygen required 103 mm Hg falling to 61 mm Hg by 40 000 ft. 40 000 ft + 100% Oxygen supplied by pressure
breathing -
The above figures refer to the actual height. Modern aircraft are pressurised to a cabin altitude of approximately 6 - 8000 ft. The temperature is easily controlled and mental functions can be retained. Some older people or those who suffer from respiratory disease may suffer from Hypoxia at these levels. In an ideal world, the aircraft would be pressurised to sea level. In reality this is impracticable because of the weight and strength parameters that would have to be achieved.
Hypoxia
Hypoxia occurs when the Oxygen available in the blood supply is insufficient to meet body tissues needs. The greatest risk of Hypoxia to a pilot is normally a result of a rise in altitude associated with a fall in pressure. Early signs of Hypoxia are related to the higher mental functions and are similar to those of alcohol. The rate of onset depends on the altitude:
15 000 ft The signs and symptoms are relatively slow in onset and difficult to detect.
40 000 ft The signs and symptoms are so quick that an individual may not recognise what is happening.
In 1979 a Beech Super King Air was flying westwards at FL 310 along the south coast of England on a conversion exercise. As it approached Exeter the crew asked ATC for permission to practise an emergency descent. This was granted and they were instructed to execute a right hand turn and contact Exeter ATC as they initiated descent. The crew acknowledged this instruction, adding that they 'would be out of contact for a few seconds as they would be donning masks and things'. Shortly afterwards the aircraft entered a turn to the left, which became a left orbit. The aircraft continued to orbit left for the next 6 hours, slowly
