The learning lesson promised a curve that this module would draw in full. Here it is: performance plotted against arousal, an inverted U with poor performance at both ends and a single optimum between them. This lesson defines the axis (arousal, and the stress that drives it), the machinery behind it (the autonomic nervous system and the fight or flight response), and the inputs that push a pilot along it: the stressors, from cockpit noise to a funeral at home.
Three questions from this lesson — one straightforward, one that applies it, one that pushes a little further. Nothing is recorded, and you can draw a new set as often as you like.
Is the stress experienced from a particular demand the same for everyone?
What explains the differences in stress levels experienced by different individuals facing the same demand?
According to the stress model, what actually determines the amount of stress experienced in a task?
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Arousal is defined as the measure of the human being's readiness to respond. At low arousal levels (just after waking, or during extreme fatigue) the attentional mechanism is not very active: processing of sensory information is slow, the nervous system is not fully functioning, the environmental scan is slow and information gets missed, so performance is low. At the optimal arousal level we are at our most efficient: enough demands to keep attention engaged, and the capability to deal with complex tasks.
Push past the optimum and performance deteriorates. Errors are made, information is missed, and attention suffers its characteristic failure: narrowing onto a limited source of data. At very high arousal the pilot reaches overload, the limit of processing capacity, and attention funnels to whatever is perceived as the primary task, so peripheral and non-attended sources go unread. The syllabus point worth its bold: at these levels the attention mechanism can reject vital information solely due to overload, with no decision ever being taken to ignore it.
Underload is the left limb of the curve, and it occurs whenever the task demands too little: the hours of a long automated cruise (a problem the automation lesson returns to), the first minutes after waking, the depths of fatigue, or simple boredom. Its dangers are the low-arousal failures: a slow scan, missed information, sinking vigilance and, over time, a drift out of the mental picture the flight depends on. Stimulation turns out to be a genuine need, not a luxury: volunteers kept in stimulus-free environments regress toward an infantile state, and the active person who retires often becomes bored and irritable, sometimes to the point of chronic illness.
One boundary deserves care. The vigilance decrement (most of it inside the first fifteen minutes of a watch) was traditionally blamed on underload and boredom, but the modern reading is different: sustaining attention is itself demanding work, and the decrement arrives even when the watchkeeper is anything but underloaded. Underload's dangers are real, but they are the slow-scan dangers above, not the explanation for the decrement.
Stress is commonly defined as the body's responses to the demands placed upon it, and anything that causes it is a stress factor, or stressor. The body constantly works to hold its physiological equilibrium (homeostasis); when outside conditions strain those mechanisms or overwhelm them, physical stress results. And stress is a natural human reaction, indeed a natural requirement of life: a certain amount keeps us aware and vigilant, animals stripped of all stimulation pine away, and only too much of it harms. Stress can be good or bad, and most stressors raise the arousal level, which is why the curve above carries both names on one axis.
The syllabus model of stress is a pair of perceptions. Stress arises from the evaluation of the demands a person perceives to be placed on them against the ability they perceive they have to cope: it is the perceived demand, not the actual demand, and the perceived ability, not the actual ability, that set the stress level. The model's feedback loop matters just as much: successfully completing a task that was perceived as difficult lowers the perceived demand and raises the perceived ability, so the same situation stresses the same pilot less the next time. Experience, in this precise sense, wards off stress.
Because perception sits in the middle of the model, stress is subjective: the stress experienced from a particular demand varies among individuals, and even within one individual from one occasion to another. The differences trace to a person's inborn and learnt characteristics (the personality dimensions of the previous lesson among them). Tolerance of stressors is shaped by the same list: the inborn and learnt characteristics themselves, the experience already banked against similar situations, the perception of one's own ability, and the body's limited, person-to-person ability to adapt to repeated moderate stress (the resident beside the airport stops hearing the aircraft that a visitor cannot ignore). Two more facts complete the picture: stress is cumulative (a second stressor raises the level disproportionately, even if the first situation has been resolved) and it transfers between situations (an argument on the ground rides along into the air), and both facts return in detail in the next lesson.
The physiological response to stress is generated by the fight or flight response, and it runs through the autonomic nervous system (ANS): the system that controls respiration, circulation, digestion and the other essential functions over which we normally have no conscious control, and that maintains homeostasis. The ANS divides into two branches with complementary jobs. The sympathetic branch provides the body with the resources to cope with a new and sudden source of stress (this is the fight or flight response itself), preparing body and mind for immediate physical activity. The parasympathetic branch prolongs the mobilisation, buying time to find a solution, and restores normal functioning once the perceived danger has passed.
The trigger is hormonal: the adrenal glands secrete adrenaline, which releases the liver's sugar reserves and drives the classic bodily reactions: the pupils dilate, saliva flow is inhibited, heart rate rises, breathing deepens and quickens, the bronchi dilate, peristalsis and bladder contraction are inhibited, blood pressure rises, blood flow to the muscles increases, the muscles tense, and the senses sharpen. It is a primitive mechanism, common to all animals and built for physical action, with only indirect effects on the brain — but those effects are useful ones: accelerated brain activity, improved quality of immediate decisions, a faster decision-making process, improved memory and improved alertness.
Plot performance against stress and the arousal curve reappears, inverted U and all, with one addition: a named break point at the optimum. With little or no stress, vigilance drops and performance is poor. As stress rises, performance rises with it (this is the motivating, medium-stress region — and the influence runs both ways: the difficulty of the task and the individual's arousal in turn shape motivation, the thread the personality lesson left for this module, while the learning lesson already showed excessive motivation manufacturing stress)up to the break point, beyond which any further rise in stress degrades performance. The break point is where overload begins: the moment the demands pass the capacity, the same arousal that was sharpening the pilot starts narrowing them instead. The exam wants the relationship both ways: stress up to the break point improves performance; stress beyond it costs performance.
The syllabus sorts stressors into five basic categories: physiological, cognitive, non-professional, imaginary and organizational. Physiological stressors split into external factors (noise, temperature, vibration), also known as environmental stress, and internal factors: hunger, thirst, fatigue, lack of sleep and pain. All of the internal five except pain are normally within aircrew control, which is why the rule is absolute: never start a period of duty with any of them. (Fatigue gets its own treatment in the next lesson, building on the sleep lesson's foundations.)
Cognitive stressors differ from the physiological ones because they depend on the operator's professional knowledge, experience and skill. They arise in the cockpit under three conditions: the situation is unexpected and no procedure exists to resolve it; the solution is realized but the pilot lacks the time or capacity to apply it (the overloaded case); or the solution is applied and the results are not as expected, leaving the problem unsolved. The level of cognitive stress depends on the individual's inborn and learnt characteristics (sensitivity, and the realization that one's knowledge may not cover the problem) and on the time available: lack of time is itself an additional stressor, and it often leads to risk taking.
Imaginary stress is anxiety: stress suffered without any stressor present, built from the sense that a future risk exists together with a felt inability to cope or a lack of self-confidence. The dog trembling at the vet after one painful visit, and the perfectly healthy patient dreading the dentist, are both running the same machinery, and a single sense impression (a scene, a noise, a smell) can resurface an old anxiety and distort perception; the apprehension can be strong enough to trigger the full physiological stress response. The next lesson takes anxiety and its effects on performance in full.
Organizational stress comes from the company. Financial pressure shows up as carried unserviceabilities, duty hours stretched to the limit and checks rushed for a slot; in one extreme case an airline president ordered flights below legal minima in bad weather, told crews to ignore maximum take-off weights and cut the minimum fuel reserves, and the airline suffered three serious accidents in short order. When management pressure like this becomes chronic, the whole company develops organizational stress, and its symptoms are poor industrial relations, absenteeism and an increased accident and incident rate. For the individual pilot the organizational sources include sudden high workload (an emergency, worse if the pilot feels undertrained for it, which is why realistic simulator training matters), long-term high workload, rostering that disrupts home life, and poor relationships or communications with management and colleagues; cockpit voice recorders have caught crews arguing on the flight deck just before accidents. The surveyed sources pilots themselves name: lack of control over events, scheduling and rostering, insufficient hands-on flying, anxiety over courses and checks, the home-to-work interface, career prospects, lack of responsibility and decision making, and fatigue and flying patterns.
The environmental stressors of the flight deck compound each other (the negative consequences of one lower resistance to the others), and the syllabus wants four discussed. Temperature: comfort for most people in normal clothing sits around 20°C; above 30°C heart rate, blood pressure and sweating increase, and below 15°C the individual becomes uncomfortable and may lose feeling and fine muscle control in the hands. Noise: some noise actually helps when a pilot is bored or fatigued (it raises arousal), but excessive noise, above about 90 dB, disrupts performance: concentration breaks up, information held in working memory degrades (raising workload), and crew errors increase. Aircraft warning design walks the same line: attract attention without startling the crew.
Vibration causes fatigue and degrades visual and motor performance; the frequency determines which parts of the body are affected, the magnitude how severely. The bands the syllabus quotes: 1-4 Hz interferes with breathing, 4-10 Hz brings chest and abdominal pain, 8-12 Hz backache, and 10-20 Hz headache, eyestrain, throat pain, speech difficulty, muscular tension and degraded visual acuity. Two resonance notes complete the set: whole-body resonance at 30-40 Hz interferes with the human responses, and applied to the head it can degrade visual acuity even though no physical damage is done to the eye; the skull's own resonance (approximately 1-4 Hz) may also affect vision. Anti-vibration seat mountings reduce the exposure, and helicopter pilots (rotor, gearbox and engine frequencies in all three axes) are particularly susceptible.Low humidity: cabin air is drawn from outside air as cold as -30 to -55°C, so its relative humidity can be as low as 5 percent, against the 40 to 60 percent the body finds comfortable; cockpit humidity typically runs 5 to 15 percent. Mucous membranes dry out, eyes turn sore (contact-lens wearers suffer first), and allergies and asthma can be aggravated, so crews should drink enough fluid to stay comfortable, remembering that caffeine and alcohol both dehydrate. One performance note rounds it off: humid environments are poor for performance regardless of temperature; dry and warm surroundings are the most conducive.
Stress crosses the front door in both directions: trouble at home flies with the pilot, and a hard roster comes home. The principal causes of domestic stress are the heavy life events: bereavement above all (the loss of a spouse, partner or child produces higher stress than any other event), followed by divorce and marital separation, the death of a close family member, personal injury or illness, and onward through marriage, job loss, retirement, pregnancy, financial change and moving house. Life-event scales weight these (the loss of a spouse, partner or child at the top with 100, divorce 73, marital separation 65) and, because stress is cumulative, the weights of the past months are added together; airlines take the top of the scale seriously enough that a pilot suffering such a bereavement may be removed from flying duties for a time. Two cautions attach: the weightings were drawn from an average western life, and cultures differ markedly, so the numbers are a guide rather than a measurement; and a pilot under domestic stress should know it can reach their concentration and performance at the controls, and use every facility available rather than carry it alone.
The inverted U and the break point are drawn or described in almost every sitting; the fight or flight physiology (which branch does what, and what adrenaline changes) is the standing physiology item; and the five stressor categories with the environmental values (90 dB, the temperature and humidity numbers) fill the recall slots. The overview, following the learning objectives:
Explain arousal and its relationship with performance
Explain when underload occurs and its possible dangers
Explain stress as a natural reaction, and the perceived-demands model
State that stress varies among individuals and explain why; list tolerance factors
Describe the fight or flight response and the ANS's role in it
State the stress-performance relationship and discuss the break point
State the basic categories of stressors
List and discuss the major environmental stressors of the flight crew compartment
Name the principal causes of domestic stress