ATPL 040 Human Performance common mistakes
ATPL 040 Human Performance · Understand the traps and how to avoid them.
When a question asks what happens to the partial pressure of oxygen in the alveoli as altitude increases, candidates answer from the general rule that 'oxygen partial pressure falls with altitude' instead of calculating it. They treat the fall in barometric pressure and the fall in inspired oxygen partial pressure as a single step, and so miss the further drop caused by water vapour and carbon dioxide in the alveoli.
The formula for alveolar oxygen partial pressure is memorised as a symbol string without the physical meaning of each term. Candidates do not picture that humidification of inspired air adds a fixed water-vapour pressure and that alveolar carbon dioxide displaces oxygen in the same total pressure, so they cannot see why alveolar oxygen partial pressure falls faster than the ambient pressure.
What to do instead
Practice writing the alveolar gas equation from memory and computing it for at least three altitudes (for example sea level, 10 000 ft, 25 000 ft). For each term, state in one sentence what it represents and how it changes with altitude. Check the answer for plausibility: at any altitude, alveolar oxygen partial pressure must be lower than inspired oxygen partial pressure, and the gap must be roughly the water-vapour and carbon-dioxide contributions.
Candidates confuse the symptoms of hyperventilation with those of hypoxia and choose 'hypoxia' as the cause of dizziness, tingling in the hands and feet, and a feeling of breathlessness in a stressed pilot. They also miss that hyperventilation lowers carbon dioxide and so causes cerebral vasoconstriction, which itself produces hypoxia-like symptoms.
Both conditions share dizziness, visual disturbance, confusion and a sense of breathlessness, and the textbook lists overlap. Candidates learn the two lists separately and never build a discriminating feature, so under exam time pressure they match on the shared symptoms and ignore the tingling, the cold clammy feeling and the absence of cyanosis.
What to do instead
Build a two-column comparison table of hypoxia versus hyperventilation and add a third column of discriminating features (peripheral tingling and paraesthesia, carpopedal spasm, no cyanosis, rapid deep breathing versus cyanosis, slow deterioration, impairment of night vision first). Then learn the operational rule: if in doubt at altitude, treat as hypoxia first with 100% oxygen and check the breathing, because hypoxia kills faster.
When asked to interpret a decompression scenario, candidates state that the oxygen mask protects against decompression sickness, or they state that a rapid decompression is more dangerous mainly because of the noise. They fail to separate the immediate threat (hypoxia and evolved-gas expansion in the lungs and gut) from the delayed threat (decompression sickness from nitrogen bubbles).
The several consequences of decompression are studied as a single block, so the time course of each is lost. Candidates do not link each consequence to its mechanism, and therefore cannot say which one drives the immediate action of donning the mask and descending.
What to do instead
For decompression, write a timeline with three columns: immediate (seconds, hypoxia, lung overpressure if the breath is held), early (minutes, cold, fogging, ear and sinus barotrauma, bends beginning), and delayed (hours, decompression sickness, neurological and pulmonary forms). For each entry, state the mechanism and the countermeasure. Then practise scenario questions by naming the threat first and the action second.
Candidates answer questions about spatial disorientation by choosing the correct name of the illusion (for example somatogravic illusion, Coriolis illusion, leans) but then give the wrong recovery action, such as 'trust your sensations and level the wings' or 'look outside and correct'. They also mix up which illusion is caused by linear acceleration and which by angular acceleration in a rotating head movement.
The illusions are memorised as a vocabulary list with no link to the underlying vestibular organ. Without a model of which receptor (otoliths for linear acceleration and gravity, semicircular canals for rotation) is being fooled, the name and the trigger cannot be matched, and the recovery rule is not connected to the fact that the senses are unreliable.
What to do instead
For each illusion, write the receptor, the stimulus, the false sensation and the correct instrument response. Fix the general rule in memory: in instrument conditions, believe the instruments, cross-check, and make smooth small corrections. Practise the specific pairings until they are automatic: somatogravic from linear acceleration on take-off or go-around, Coriolis from head movement during a turn, leans from a prolonged coordinated turn followed by a correction.
On questions about the SHELL model, candidates describe the model as a list of four factors and then treat 'liveware' as only the pilot. They miss that liveware interacts with liveware (crew), with software (procedures, checklists, manuals), with hardware (controls, displays, seating) and with environment, and they cannot place a given scenario on the correct interface.
The model is learned as a diagram to be labelled rather than as an analytical tool. Candidates do not practise taking a real occurrence and asking which interface failed, so they cannot map an exam scenario onto the model.
What to do instead
Take five short occurrence descriptions and, for each, write which SHELL interface broke down and why. Note that liveware-liveware covers communication, leadership and teamwork, and that liveware-software covers documentation and automation logic. This turns the model into a classification skill rather than a recall item.
Candidates classify an error as a 'violation' when the behaviour was an unintended slip or lapse, and classify a deliberate shortcut as a 'mistake'. They also confuse the slip (correct intention, wrong execution) with the lapse (omitted step) and with the mistake (wrong intention or wrong plan).
The error taxonomy is memorised from a table without a decision procedure. Candidates do not ask the two key questions in order: was the intention correct, and was the action executed as intended? Without that order, the categories overlap in their minds.
What to do instead
Learn a short decision tree. First ask: was the intention correct? If not, it is a mistake (rule-based or knowledge-based). If yes, ask: was the action executed as planned? If not, it is a slip (wrong action) or a lapse (omitted or forgotten action). Separately, ask whether the behaviour deviated from a rule that the person knew and chose to break; only then is it a violation. Apply the tree to ten short examples.
Candidates answer workload questions by equating high workload with high performance, or by assuming that automation always reduces workload. They miss the inverted-U relationship and the finding that automation can shift workload to monitoring and can create new workload in programming and mode awareness.
Workload is studied as a vague concept without a graph or a measurement method. Candidates do not distinguish mental demand, time pressure and effort, and they do not link workload to arousal and performance.
What to do instead
Draw the arousal-performance curve and mark underload, optimum and overload, and write one aviation example for each region. Then list the ways automation can increase workload (programming, monitoring, mode confusion, reduced manual skill) as well as reduce it. Practise questions by asking which phase of flight and which task demand is being described before choosing an answer.
On fatigue and circadian questions, candidates answer that a pilot can adapt fully to night shift, or that fatigue is mainly a matter of willpower. They underestimate the circadian low in the early morning, the effect of sleep debt, and the difference between acute fatigue and chronic fatigue.
The physiology of the body clock is learned as a list of facts without the operational consequences. Candidates do not connect the circadian low to the timing of known accidents, so they cannot reason about a roster or a rest period.
What to do instead
Learn the circadian rhythm curve with its low in the early hours and its secondary dip in the early afternoon, and note that adaptation to night work is partial and slow. Distinguish acute fatigue (recoverable with one good sleep) from chronic fatigue (accumulated sleep debt, needs extended rest). Practise by evaluating a sample roster and stating the highest-risk sector and why.
In crew resource management questions, candidates give the socially desirable answer ('the captain should assert authority', 'the first officer should speak up') without naming the specific behaviour. They do not distinguish assertiveness from aggression, and they do not describe a structured communication technique such as a graded assertion or a closed-loop readback.
CRM is treated as general attitude rather than as observable behaviour. Candidates have no vocabulary of specific techniques, so they choose the option that sounds most responsible rather than the most operationally precise.
What to do instead
Learn named techniques and be able to describe each in one sentence: graded assertiveness (for example the PACE or similar escalation), closed-loop communication with readback, the sterile flight deck rule, briefing with threats identified, and the two-challenge rule. For each, write what the speaker says and what the listener must do. In questions, prefer the option that names a concrete behaviour over the one that names a virtue.
On threat and error management questions, candidates treat a threat and an error as the same thing, and they do not distinguish a countermeasure applied before the error (avoidance) from one applied after (trapping or mitigating). They also answer that the absence of an accident means the flight was error-free.
TEM is memorised as three words without a model of the sequence threat, error, undesired aircraft state. Candidates do not see that errors are normal and that safety comes from detecting and managing them, so they cannot place a scenario in the sequence.
What to do instead
Write out the TEM chain and place ten example events on it, marking whether the countermeasure was avoidance, trapping or mitigation. Learn the distinction: a threat is external to the crew's influence and occurs before or during the flight; an error is a crew action or inaction. Then practise stating, for each scenario, the threat, the error, the undesired state and the countermeasure.