Aviation Psychology and Human Factors

1. Introduction to Aviation Psychology

Aviation Psychology is a specialty in applied psychology that focuses on understanding human behaviour, emotions and mental states as they relate to the operation and control of aviation systems and their influence on the safety and efficiency of flight.

The aim of aviation psychology is to understand and to predict the behaviour of individuals in an aviation environment. Its study is aimed at improving safety, efficiency and comfort.

Practitioners of aviation psychology bring the tools and techniques of psychology to bear in order to describe, predict, understand and influence the aviation community to achieve those aims.

2. Human Error & Human Reliability

It has long been accepted that human errors are inevitable. The majority of pilot-related errors are considered to be failures of:

• Interpersonal skills
• Communications
• Decision-making
• Leadership

This does not mean that the frequency of error cannot be reduced, or that the effects cannot be avoided or mitigated.

flowchart LR
  A[Pilot Error
Origins] --> B[Interpersonal Skills]
  A --> C[Communications]
  A --> D[Decision-Making]
  A --> E[Leadership]
  B --> F[Mitigation:
Superior Judgment]
  C --> F
  D --> F
  E --> F
  F --> G[Safe Flight Outcome]
  

3. Workload

Workload = the amount of mental effort needed (and expended) to process information. Here we discuss cognitive (mental) workload, as opposed to physical workload. Workload is linked to almost all other areas within cognition and performance, particularly attention, vigilance, fatigue, decision-making and multi-tasking.

3.1 Four General Task Factors Affecting Workload

1. 'Difficulty' of the task
2. Number of tasks running in parallel (concurrently)
3. Number of tasks in series (switching from task to task)
4. The time available for the task (speed of task)

Indirect factors also play a role: duration of task, fatigue and level of arousal.

3.2 Symptoms of Increasing Workload

• Attention and task focusing
• Task shedding and re-prioritization
• Implications for Situation Awareness
• Increased use of decision short-cuts and less scrutiny or review
• Increased fatigue and chance of error

The area that deals with all such activity is called the working memory ('Information Processing').

4. Information Processing — A Functional Model

We receive information from the world around us through our senses: sight, hearing, touch, smell and taste. The "Gestalt laws" formulate basic principles governing how objects are mentally organised and perceived.

4.1 The Five Stages of Reasoning

1. Detection
2. Perception
3. Decision Making
4. Action (responses are selected and executed)
5. Feedback

flowchart LR
  S[Sensory Input
Sight / Hearing / Touch /
Smell / Taste] --> D[1. Detection]
  D --> P[2. Perception]
  P --> DM[3. Decision Making
Working Memory]
  DM --> A[4. Action
Response Executed]
  A --> F[5. Feedback]
  F -.alters action.-> DM
  LTM[(Long-Term Memory)] <--> DM
  STM[(Short-Term Memory)] <--> DM
  

4.2 The Brain — Central Decision Maker & Response Selection

Once information has been perceived a decision must be made as to the response. Information is continuously entered into and withdrawn from both long-term and short-term memories to assist the decision process. The decision involves input, processing, actions and feedback. The information comes from many sources and requires conscious processing in working memory. A problem at any stage of information processing could affect the outcome.

To carry out multi-tasks we must learn skills through Motor Programmes.

4.3 Stimuli

The senses provide stimuli to our brain which has the ability to retain them for a short time, from the time they arrive. We may not have the processing capacity to deal with them all.

5. Types of Memory & Sensory Memories

5.1 The Three Types of Memory

• Sensory memory
• Short-term (or working) memory
• Long-term memory

5.2 Receptors & Sensory Memories — Key Features

• There is a separate memory store for each sensory system.
• The input decays rapidly.

The sensory stores for sight and sound are the most important, and knowledge of these is necessary.

5.3 Information Processing Model — Diagrammatic View

5.4 Sensory Memory for Sight — Iconic Memory

The Iconic Memory is the visual sensory store. It only lasts for between 0.5 and 1 second.

70–80 % of the information processed by humans is received through the visual channel.

5.5 Sensory Adaptation (Habituation)

All senses adapt, either partially or completely, to their stimuli after a period of time.

6. Anticipation & Perception

6.1 Perception

Perception involves the conversion of the sensory information received into a meaningful structure.

Sensory information that we expect to receive is more easily perceived and integrated when it actually occurs, compared with totally unexpected information.

"We can 'perceive' only that which we can 'conceive', but we perceive only a fraction of the information reaching our senses at any moment."

The process of perception is greatly assisted by our ability to form mental and three-dimensional visual models.

6.2 Funneled Perception

Perception of a situation can differ depending upon the starting point of an observer.

7. Attention

Attention is the process of directing and focusing psychological resources to enhance perception, performance and mental experience. To pay attention to something is to concentrate on it — a stimulus, threat, decision or calculation. Critically, attention is limited; if some attention is being used for one thing, it cannot be used for something else.

7.1 Types of Attention

1. Selective Attention — inputs are sampled continually to decide their relevance to the present task at hand.
2. Divided Attention — when our central decision-making channel can time-share between a number of tasks, executing several mental activities at almost the same time (e.g. switching attention from outside the aircraft to the airspeed indicator and monitoring the progress of a motor programme such as flying or taxiing on a relatively subconscious level, while making a radio call at the same time).

The human brain has different reservoirs of resources for information-gathering, information-processing, or the action phase.

7.2 Lack of Attention

The major danger for pilots is the poor management of attention.

7.3 Attention Mechanism — Why It Is Required

Because of two potentially limiting stages in processing information:

1. There is a limit to the number of items held or maintained in short-term memory (working memory).
2. Our channel capacity is limited.

7.4 Choice of Item

Attention is the deliberate devotion of cognitive resources to a specific item. Although attention can move very quickly from item to item, it can only deal with one at a time — so the pilot must consciously prioritize.

7.5 The Cocktail Party Effect

With many conversations occurring all around, one conversation can suddenly break through to attention because a word or phrase was particularly meaningful — the classic example is a person hearing their own name mentioned in another conversation that they were not paying attention to.

8. Vigilance & Complacency

Vigilance = the capability to be sensitive to potential changes in one's environment, i.e. the capability to reach a level of alertness above a threshold for a certain period of time — rather than the state of alertness itself.

8.1 Hypo (Low) Vigilance

Mainly due to the monotony of the task, tiredness, the need for sleep and a lack of stimulation. It may occur at any moment of the flight. Decrease in sensory perception and sensation of muscular heaviness are indications of low vigilance.

A state of high fatigue is liable to cause phases of drowsiness and hypo-vigilance, which result in a reduction of performance and unconscious phases of micro-sleep.

8.2 Hyper Vigilance

In its most acute forms, an extremely agitated state of panic or near panic. Characterised by indiscriminate attention to all sorts of minor and major threat cues, as the person frantically searches for means of escaping the anticipated danger.

8.3 Optimum Vigilance

Lies somewhere between hypo and hyper vigilance.

8.4 Complacency

A state of self-satisfaction with one's own performance coupled with an unawareness of danger, trouble or controversy.

flowchart LR
  A[Vigilance Spectrum]
  A --> H[HYPO
Drowsiness, Micro-sleep
Cause: Monotony, Fatigue]
  A --> O[OPTIMUM
Best Performance]
  A --> Y[HYPER
Panic, Indiscriminate Attention]
  H -.->|risk| C[Complacency
Low workload, Automation]
  Y -.->|risk| R[Regrettable Decisions]
  

9. Motor Programmes (Skills) — Anderson Model

Motor Programmes, or "Skills", are behavioural sub-routines which are learnt by practice and/or repetition and are held within the Long-Term Memory. They can be carried out without conscious thought.

In the initial phase of flight training the pilot is competent enough to fly the aircraft at this stage but does neither have a great deal of confidence in his/her abilities nor in the whole system.

9.1 Anderson Model — Three Phases

1. The Cognitive Phase
2. The Associative Phase
3. The Automatic (Autonomous) Phase

flowchart LR
  C[a) Cognitive Phase
Conscious effort,
understanding rules] --> AS[b) Associative Phase
Refinement,
fewer errors]
  AS --> AU[c) Automatic Phase
Subconscious execution,
resources freed for new tasks]
  AU --> SKILL[Stored as Motor Programme
in Long-Term Memory]
  

10. Reflexes, Reaction Time, Surprise & Startle

Reflexes occur with little or no involvement of the central nervous system.

10.1 Reaction Time

There is a delay between detection, stimulus and muscle contraction called reaction time. Reaction time depends on the type of reflex action being used.

10.2 Three Types of Reflex Actions

10.3 Surprise and Startle

The startle reflex is a reflex-like event that blinks the eyes and causes a whole-body 'jerk' to occur (similar to that sometimes caused in sleep). The reflex has a relatively basic neural pathway from the sense organ. Many things can cause (or contribute to) a startle reflex:

• Sudden noises
• Unexpected tactile sensations
• Abrupt shocking perceptions
• The sensation of falling
• An abrupt visual stimulus

There is little evidence that a startle reflex alone creates much of a sustained or lasting impact on cognitive functions, although there are some minor and short-lived physiological changes such as raised heart rate.

10.4 Effects on Pilots

The main effects of the pure startle reflex on pilots are:

• Interruption of the on-going process.
• Distraction of attention toward the stimulus.

These happen almost immediately and can be quickly dealt with if the cause is found to be non-threatening.

11. Quantitative Overload & Human Reliability

Quantitative Overload — a very high workload can be interpreted as 'Stress'.

11.1 Most Common Symptoms of Overload

• A sharp degradation of performance
• Funneling of attention or focus
• Regression
• Mental "blocking"
• Mood swings
• Restlessness and trembling
• Panic

11.2 Human Reliability

The rate of human error during simple and repetitive tasks might be expected to be 1 in 100, but after practice, a rate of 1 in 1,000 could be achieved.

11.3 Error Generation

Errors tend to be cumulative. One slip rarely stays isolated — it sets up the next.

12. Short-Term & Long-Term Memory

12.1 Short-Term Memory (Working Memory) — 10 to 20 Seconds

Short-term memory enables information to be retained for a short period of time. That information will be lost in 10 to 20 seconds unless it is actively rehearsed and deliberately placed in our long-term memory.

Auditory information is considered easier to retain than visual information as it is easier to rehearse sounds than data in a visual form.

12.2 Limitations of Short-Term Memory

The capacity of our short-term memory is limited. The maximum number of unrelated items which can be maintained in the short-term memory is about 7 ± 2. Once this limit is exceeded one or more of the items are likely to be lost or transposed.

12.3 Methods of Increasing Short-Term Memory

12.4 Long-Term Memory — Unlimited Time Period

It is believed that information is stored in the Long-Term Memory for an unlimited time period, although frequently there may be retrieval problems.

12.5 Three Subtypes of Long-Term Memory

13. Learning, Retention & Motivation

13.1 The Learning Process

Learning is an internal process which allows the mental acquisition and retention of data. Types include:

Insight

The data is intellectually and cognitively understood and is retained. Observational Learning / Imitation — data from an outside source is replicated. Experience — learning from our mistakes.

Skill Learning

Involves motivation, attention, observation, much practice and corrective feedback.

13.2 Retention of Information

Retention can be increased by:

1. Mnemonics — the practice of improving or helping the memory, or the systems used to achieve this.
2. Memory Training

13.3 Motivation

Motivation is the combination of a person's desire and energy directed at achieving a goal. It is the cause of action.

Not all people are motivated by the same thing and over time their motivations might change.

14. Experience, Response, Cognition & Hallucination

14.1 Experience

We all have the ability to learn from our experiences and mistakes, and from those of others.

14.2 Response

Any response will cause a detectable change which, in turn, will be noted by the senses. The feedback may alter the action being taken.

• Auditory stimuli (noises) are more likely to attract attention than visual stimuli, but they are also more likely to be responded to in error.
• An increase in age between 20 and 60 years tends to lead to slower but more accurate responses.

14.3 Response Error (Error of Commission)

If an unexpected stimulus occurs, we will be more likely, under pressure, to make an error of commission.

14.4 Response Times

Response to reaction time is the interval between the onset of a given signal and the production of a response to that signal.

14.5 Cognition in Aviation

Cognition = the mental faculty or process of acquiring knowledge by the use of reasoning, intuition or perception. In aviation, flight puts the pilot into an environment which can distort sense organs, and the changed perspective which is experienced in flight can result in information being presented which is outside the individual's expectations.

14.6 Hallucination

A hallucination is actually a false perception characterised by a distortion of real sensory stimuli. (Not a fabrication of stimuli — the stimuli are real, but their perception is distorted.)

14.7 Workload and Limitations

Too high or too low a workload can result in degraded performance. Several types of situations may cause mental overload.

15. Judgment & Decision Making

Making good decisions is one of the important aspects of piloting an aircraft. Good decisions can help lead to safe, successful flights, whereas bad decisions and even indecision have led to many aircraft accidents. Talk to your instructor and other pilots about different flying situations to obtain advice about what a good decision would be in a given circumstance.

When flying with another pilot, it is possible to increase the chance of a good decision being made by discussing the potential problems beforehand. If as an inexperienced pilot you are flying with someone of more experience and you see him doing something you consider to be dangerous, you should immediately question their course of action.

15.1 Risk Assessment

Risk assessment is based on:

• The probability of the risk occurring.
• The impact of that risk if it did occur.

You will have to weigh up the risk and the possible consequences of the risk in order to determine your course of action.

flowchart TD
  A[Identify Risk] --> B{Probability
of Occurrence}
  A --> C{Impact
if it Occurs}
  B --> D[Combine Probability × Impact]
  C --> D
  D --> E{Acceptable?}
  E -- Yes --> F[Proceed with Mitigation]
  E -- No --> G[Modify Plan / Don't Fly]
  

16. Personality, Attitude & Situational Awareness

16.1 Personality, Attitude and Behaviour

Someone who is too introverted or anxious may not make a good pilot. Examples of desirable characteristics in a pilot are:

• The ability to cope with stress and adventure.
• The ability to assess and control risks.

As captain of an aircraft, you will need to show good leadership skills.

16.2 Situational Awareness

A good leader displays good situational awareness and accurately assesses his own performance. The following factors can interfere with accurate situational awareness:

1. Stress
2. Boredom
3. Fatigue
4. Emotional disturbance
5. Poor communication
6. Interruptions

17. Mechanics of Decision Making

Pilots operate in a dynamic and constantly changing environment. A good decision reached a minute ago will not necessarily be the same good decision in two minutes' time.

17.1 The Seven Steps

1. Recognize and identify the problem — have a clear definition of what needs addressing.
2. Consider the nature of the problem — type of issue, why it needs a decision, hoped-for results.
3. Analyze or research the problem — gather all information so informed choices can be made.
4. Develop a list of possible solutions — list decisions and their consequences.
5. Select the best alternative — choose the best solution for the situation.
6. Execute the best choice — taking action is often the hardest part.
7. Follow up and communication — keep the process going with constant communication; Feedback determines the overall success of and reaction to the decision.

flowchart LR
  S1[1. Recognize
& Identify] --> S2[2. Consider
Nature]
  S2 --> S3[3. Analyze
/ Research]
  S3 --> S4[4. List Possible
Solutions]
  S4 --> S5[5. Select Best
Alternative]
  S5 --> S6[6. Execute
Best Choice]
  S6 --> S7[7. Follow Up &
Communicate]
  S7 --> FB[Feedback]
  FB -.re-evaluate.-> S1
  

18. Communication & Team Work

When piloting an aircraft — whether with a passenger, another pilot or an instructor — good verbal communication will help the flight go more smoothly and contribute to flight safety.

Concise and unambiguous communication is essential to the safe conduct of air traffic.

18.1 Barriers to Communication & Team Work

Several things can be done by team leaders to facilitate good teamwork. In the end, it is the team leader who takes the decisions on behalf of the team.

18.2 Expectation

19. Automation

Automation refers to a system or method in which many of the processes of production are automatically performed or controlled by self-operating machines, electronic devices, etc.

Through microprocessor technology, navigational tasks and aircraft system management have been automated, making the flight crew more peripheral to the actual operation of the aircraft. Pilots who at one time had direct authority over all aspects of aircraft control and management have now become responsible for the management of complex hardware and software interfaces.

These technological advances have given rise to new forms of error. Automation is almost always introduced with the expectation of reducing human error and workload, but what frequently happens is that the potential for error is simply relocated. More often than not, automation does not replace people in systems; rather, it places the person in a different, and in many cases, more demanding role.

19.1 Definition of Automation

"The technique of controlling an apparatus, a process or a system by means of electronic and/or mechanical devices that replaces the human organism in the sensing, decision-making and deliberate output."

19.2 Evolution of Transport Aircraft Automation

19.3 Mismatch Between Automation and the Human Element

Nevertheless, a few accidents point to a mismatch between automation and the human element. Studies identified nine categories to focus on:

1. Situational awareness
2. Automation complacency
3. Automation intimidation
4. Captain's command authority
5. Crew interface design
6. Pilot selection
7. Training and procedures
8. The role of pilots in automated aircraft
9. (Studies concluded scope for improvement in fields like: human capabilities and limitations, ergonomics, cognitive suitability and instrument standardization.)

19.4 Qualities of Human-Centred Automation

Human-centred automation should possess these qualities in proper measure:

• Accountable
• Subordinate
• Predictable
• Adaptable
• Comprehensible
• Flexible
• Dependable
• Informative
• Error-resistant
• Error-tolerant

20. Human Characteristics & Cockpit Design

20.1 Personality

Personality involves two major factors:

• Neuroticism – Stable continuum
• Introversion – Extroversion continuum

Extroverts are said to be impulsive and sociable; introverts are more withdrawn and cautious.

A low-neuroticism personality is one of an emotionally stable person, whereas a high-neuroticism person will worry and get upset easily.

20.2 Cultural Differences

The way people behave, think and interact with each other generally — as well as what motivates them — will be partly a factor of their national and cultural background. One culture may value subordinates speaking up, whereas another culture may value subordinates who obey their superiors unquestioningly. The latter might perceive a subordinate who points out a concern as being impolite, aggressive or disruptive.

20.3 Competencies

The main area where personality and background culture are important is interpersonal interaction. In terms of competencies, this means communication, leadership and teamwork — crew interactions or interactions with outside agencies such as air traffic control.

20.4 Design Considerations

The following human characteristics must be taken into account in the design of aviation systems:

• Physical dimensions
• Capability for data sensing
• Capability for data processing
• Capability for motor activity
• Capability for learning
• Physical and psychological needs
• Sensitivities to physical environment
• Sensitivities to social environment
• Coordinated action
• Differences among individuals

20.5 Hardware, Design of Flight Decks, Size & Anthropometry

Therefore a great deal of attention is required to design the equipment. The most important requirement in the design of both displays and controls is STANDARDIZATION.

20.6 Anthropometry

This is the study of human measurement. The information is grouped into:

• Static measurements
• Dynamic measurements
• Contour surface measurements

It is not practical to design a cockpit for both the very short and the very tall individual. Those in the central 90 % of size distribution will be catered for. Normally the design of aircraft uses measurements taken from the entire population disregarding both the 5 % lowest and the 5 % highest.

20.7 Eye Datum

Cockpit space must be designed around a defined position of the pilot's eye. This may be called the Eye Datum, the Design Eye Position or the Reference Eye Point.

Once the design eye position has been set, the size of the cockpit can be established.

20.8 Design of Cockpit Seats

It is of the utmost importance that the seating is comfortable and adjustable to the individual pilot's size and shape. Pilots should adjust their seats to establish a comfortable position giving full control movement, with optimum instrument scan and outside visibility. This position should be used for all phases of the flight.

21. Hardware — Displays & Controls

21.1 Presentation Requirements

21.2 Conventional Analogue Standard 'T' Display

A standard 'T' layout has the artificial horizon / attitude indicator at the centre with the altimeter, airspeed indicator and direction indicator grouped around it. Digital Display and the Compass. The conventional analogue type of compass card gives a better picture of the aircraft orientation than would a digital readout.

21.3 Combination or Analogue and Digital Displays

In some instances, both digital information and analogue information can be combined in a single instrument.

21.4 Hardware, Controls — Basic Considerations

22. Stress Tolerance, Fatigue & Arousal — Well-Being of Operational Personnel

Three of the many factors which may influence the well-being of operational personnel are:

1. Stress and fatigue
2. Body rhythm disturbance
3. Sleep deprivation or disturbance

Other factors affecting physiological or psychological well-being include: temperature, noise, humidity, light, vibration, workstation design and seat comfort.

22.1 Stress, Arousal and Performance

The different stress levels generated within individuals by a particular stressor will differ. A moderate level of stress may improve performance. Stress promotes an increase in physical strength rather than promoting mental performance.

• The response of a person to the event or circumstances to which he is exposed is known as arousal.
• Arousal is a measure of a person's readiness to respond effectively to a given stress factor.
• Personality, character, training and experience will influence levels of arousal in a given individual.

22.2 The Effects of Stress

In an active, outward-going, highly trained person, too little stimulation or stress arousal will lead to the onset of boredom and even drowsiness. An introspective, under-confident person, if highly aroused, might be unable to function at all — even in circumstances that he is competent to deal with.

22.3 Stress Factors (Stressors)

Stress factors are cumulative. Stress occurs under various conditions:

• Pilot must revise his plan of action and does not immediately have a solution
• Inexperienced pilots when situational demands exceed their individual capabilities
• Pilot is convinced he will not be able to find a solution to the problem
• Physiological factors — hunger, thirst, pain, lack of sleep, fatigue

22.4 Environmental Tolerances

Temperature, pressure, humidity, noise, time of day, light and darkness can all be reflected in performance and also in well-being. Heights, enclosed spaces, and a boring or stressful working environment can also influence performance.

22.5 Managing Stress

Recognising stress, accepting it and developing a coping strategy is essential for stress management. Training and experience help to ward off stress and high levels of arousal. Successful completion of a stressful task will reduce the amount of stress experienced when a similar situation arises in the future.

22.6 Life Stresses — Psychological Scoring

Pilots suffering from life stress should be aware that this can affect their concentration and performance when at the controls of an aircraft. The descending order in which the factors affect a person:

Death of spouse/child → Divorce → Marital separation → Death of a close family member → Injury / illness → Marriage → Loss of job → Retirement → Pregnancy → Sexual problems → Birth → Change of financial status → Siblings leaving home → Change of eating habits → Change of residence → Loan/debt/mortgage → Vacations → Minor violations of law.

Note: such schemes need to be treated with caution because of wide individual variability.

22.7 Indications of Stress

Stress causes: mental blocks, confusion, channelized attention, resignation, frustration, rage, deterioration in motor coordination, high pitch voice and fast speaking.

22.8 Tiredness and Fatigue

Tiredness and fatigue, though related concepts, differ in their long-term physical effect on the body. To deal with normal tiredness it is sufficient to ensure that periods of activity and periods of restful sleep comply with the normal pattern for a person's age and physical condition.

Ordinary tiredness results from normal physical and/or mental exertion over a normal waking period. If a person is tired, a good night's sleep is the only requirement for that person to be fit the following morning.

Causes of Fatigue

• Long-term ill health, either physical or mental
• Regular sleep deprivation, for whatever reason
• High levels of stress and/or anxiety over a prolonged period
• A disturbed body cycle (e.g. jet lag, changing work shift patterns)
• Long-term difficulties in personal or work-based relationships
• A stressful living and/or working environment (e.g. high levels of noise, or unreasonable physical or mental demands)

Symptoms of Fatigue

• Memory lapses
• Frequent mistakes in speech and actions
• Rapid changes of mood
• Diminished awareness
• Tiredness
• Lack of coordination

Minimum Self-Help Program

• Accept the fact that you are fatigued
• Eat a balanced diet and healthy food
• Try to take the stress out of your life
• Make sure that you get regular, undisturbed sleep
• Avoid alcohol and caffeine
• Always consult a doctor

22.9 Arousal

Arousal is a major aspect of many learning theories and is closely related to other concepts such as anxiety, attention, agitation, stress and motivation.

23. Body Rhythm Disturbance — The Circadian Cycle

23.1 Stimuli and Attention

Our bodies are continuously receiving stimuli through our five senses. This information is stored briefly in our sensory memory and, if we perceive it to be important, it is transferred to our short-term memory or Central Decision Maker. Some stimuli are better than others at getting our attention. We can split our attention between several different things by concentrating on them in rapid succession.

23.2 The Circadian Circle

The Circadian Circle represents our level of alertness throughout the day. Circadian rhythms are internally generated by a self-sustaining (autonomous) biological clock located in the hypothalamus, which functions as the main control centre for the autonomic nervous system by regulating sleep cycles, body temperature, appetite, etc., and acts as an endocrine gland by producing hormones. It takes into account biological elements such as body temperature, heart rate and blood pressure — which affect our level of alertness during the day.

23.3 24-Hour Circadian Reference

As we sleep, our heart rate is lowered and hence our level of alertness is reduced. Blood pressure is also often lowered after mealtimes. Human performance declines at night when the body and mind desire rest.

23.4 Melatonin — "The Light of Night"

Melatonin is secreted from the pineal gland principally at night. The hormone is involved in sleep regulation, as well as in a number of other cyclical bodily activities and circadian rhythm in humans.

• Secretion increases soon after the onset of darkness.
• Peaks in the middle of the night, between 2 and 4 a.m.
• Gradually falls during the second half of the night.

This circadian rhythm of secretion plays an important role in its hormonal activity. Melatonin is exclusively involved in signalling the 'time of day' and 'time of year' (hence considered to help both clock and calendar functions) to all tissues, and is thus considered to be the body's chronological pacemaker or 'Zeitgeber'.

23.5 Trans-Meridian Flight — Pilot Considerations

24. Sleep — NREM & REM

Sleep is basically divided into two components:

• Rapid Eye Movement (REM) sleep
• Non-Rapid Eye Movement (NREM) sleep

NREM sleep is further divided into four stages from lightest to deepest. Both types of sleep are required to recoup physical and mental energy.

24.1 NREM Sleep Stages

24.2 REM Sleep (Paradoxical Sleep)

• Usually occurs 70–90 minutes into a sleep.
• Happens in cycles lasting for approximately 10 minutes initially to 1 hour.
• The eye moves rapidly from side to side and the brain wave form is similar to that when a person is awake.
• Dreams occur.

As we grow older, the time spent in REM sleep declines from 50 % of our sleep for infants, to 20 % of our sleep for adults.

24.3 Sleep Inertia

24.4 Key Points to Remember

flowchart LR
  W[Wakefulness] --> N1[NREM 1
~10 min
Transition]
  N1 --> N2[NREM 2
10–25 min
50% of sleep]
  N2 --> N3[NREM 3
Onset Deep Sleep]
  N3 --> N4[NREM 4
Deep Sleep
No eye/muscle activity]
  N4 --> R[REM
70–90 min in
Dreams · Brain wave ≈ awake]
  R -.cycle repeats with more REM each time.-> N2
  

25. Mental Health Problems & Disorders

Mental health problems and disorders among pilots, ATCOs, maintenance and other personnel in aviation may impair performance and therefore be a threat to flight safety.

25.1 Case Study — Germanwings Flight 9525

25.2 Why Pilots May Not Report Mental Health

There may be many reasons why a pilot may be reluctant to discuss mental health problems with the examining physician during the annual medical assessment, including fear of losing his or her licence with both personal and financial costs as a result. This may prevent the pilot from receiving adequate and timely help, and this could potentially make the problems worse and prolong the time for recovery.

25.3 Where to Focus Preventive Efforts

Serious mental health disorders (e.g. psychosis) are relatively rare and their onset is difficult to predict. Preventive efforts should be aimed at more common mental health problems such as:

• Depression
• Anxiety
• Substance misuse

Master Reference Tables & Mnemonics

M-1. Master Numerical Reference

M-2. Mnemonics & Memory Aids

M-3. Quick Definitions Recall Sheet

M-4. Risk Formula

M-5. Final Quick-Revision Summary Box