ATPL Human Factors (CAA) key terms

A condition in which the tissues receive insufficient oxygen. In aviation it usually results from high cabin altitude, and it impairs night vision, judgement and consciousness well before the person notices anything is wrong.

The period between loss of adequate oxygen supply and the point at which a person can no longer take effective protective action. It shortens rapidly as altitude increases and is reduced by exertion or cold.

A gradual loss of cabin pressure that may be too subtle to notice. Oxygen starvation develops insidiously while the crew feels well, making it more dangerous than a sudden, obvious decompression.

Overbreathing that lowers carbon dioxide in the blood, causing dizziness, tingling, chest tightness and visual disturbance. Its symptoms resemble hypoxia, so the safe response in flight is to assume hypoxia and use oxygen.

A mismatch between the pilot's perceived attitude and the aircraft's actual attitude, caused by misleading vestibular and visual cues without a reliable external horizon. It is most likely in low visibility and during acceleration or sustained turns.

A false sensation of pitch caused by linear acceleration or deceleration. Rapid acceleration is felt as a nose-up attitude, and deceleration as nose-down, which can provoke an inappropriate control input after take-off or during go-around.

A false sensation of turning that occurs when a sustained turn ends or when the head moves during a turn. The pilot may believe the aircraft is turning the opposite way and correct in the wrong direction.

The inner-ear organs, semicircular canals and otoliths, that sense rotation and linear acceleration. They cannot distinguish gravity from acceleration and give no reliable attitude information in prolonged turns or poor visual conditions.

A misleading perception produced by the visual system, such as a runway that appears wider, narrower, closer or further away than it is. It leads to incorrect height or approach-path judgements, especially at night or on sloping terrain.

A night approach over featureless terrain with few ground lights, where the pilot has no visual reference and tends to fly too low and too flat. The runway appears closer and higher than it really is.

The very brief store that holds raw information from the senses, typically for under a second for vision. It allows the brain to select relevant input for further processing before the content fades.

The limited-capacity store used to hold and manipulate information during a task, such as remembering a clearance while setting frequencies. It is easily overloaded, and its contents are lost quickly if not rehearsed or written down.

The large, durable store of knowledge and experience, including procedures and aircraft systems. Retrieval becomes slower and less reliable under stress or when the information was learned only by repetition without understanding.

The process that selects which information receives conscious processing. It is limited and can be captured by salient stimuli or narrowed under stress, so tasks that demand it simultaneously compete with each other.

A state of reduced vigilance arising when everything appears to be going well. It leads to skipped checks, superficial monitoring and late detection of changes, and is a common precursor of error on routine flights.

An action or omission by a person that deviates from intended or required behaviour and reduces safety margins. It is normal and inevitable, so safety depends on containing its consequences rather than eliminating it.

A framework describing how errors arise and combine, for example the skill, rule and knowledge classification or the Reason Swiss cheese model of latent conditions and active failures. Models guide countermeasures rather than blame.

Performance of highly practised, largely automatic routines that require little conscious attention, such as basic aircraft handling. Errors here are typically slips or lapses, often in the execution of an otherwise correct intention.

Performance guided by stored if-then procedures learned from training or experience. Errors occur when a good rule is misapplied or a wrong rule is chosen because the situation was misdiagnosed.

Performance in novel or ambiguous situations where no routine or rule applies and conscious reasoning is required. It is slow and resource-hungry, and errors tend to be mistakes in diagnosis or decision rather than slips.

A pre-existing weakness in organisation, equipment, documentation or training that lies dormant until combined with local circumstances and active failures. Examples include confusing displays, poor procedures and unrealistic schedules.

A framework in which crews anticipate external threats, trap errors before they affect the flight, and manage any resulting undesired aircraft state. It treats error as expected and emphasises detection, communication and recovery.

A condition in which the aircraft's position, speed, configuration or energy is outside safe parameters as a result of error. Recognising and correcting it early prevents escalation into an incident or accident.

An organisational approach that distinguishes honest error from reckless or intentional violation. It encourages reporting and learning while still holding people accountable for wilful misconduct, thereby improving safety information flow.

The process of choosing between options under uncertainty and time pressure. In aviation it benefits from structured models, clear criteria, and cross-checking with other crew members rather than relying on the first plausible option.

The tendency to keep following an original plan despite accumulating evidence that it is no longer appropriate. It contributes to pressing on into deteriorating weather or continuing an unstable approach.

The tendency to seek and interpret information in ways that support an existing belief while ignoring contrary evidence. It can delay recognition of a developing problem such as an engine malfunction or a wrong route.

The systematic identification, assessment and mitigation of hazards before and during flight. It uses tools such as risk matrices and personal checklists to balance the likelihood and severity of adverse outcomes.

The effective use of all available resources, including people, equipment and information, to achieve safe and efficient flight. It covers communication, leadership, teamwork, workload management and decision making.

The skill of stating concerns clearly and respectfully, and persisting until they are acknowledged, without becoming aggressive. It is essential for junior crew members to challenge a perceived error by the pilot flying.

The balance between a captain's authority and the crew's freedom to contribute. Too steep and crew withhold vital input; too flat and decisions become confused. Effective crews adjust it to the situation.

The captain's responsibility for setting standards, making final decisions and fostering an environment where others speak up. Good leadership is task-focused and people-focused, and adapts as workload and threat change.

A structured pre-flight or pre-approach exchange that shares the plan, allocates tasks and agrees on contingencies. It builds a shared mental model so that deviations are noticed and challenged early.

The accurate perception of what is happening now, an understanding of what it means, and a projection of what will happen next. Loss of it precedes most human-error accidents.

The mental and physical effort required to meet task demands. When demand exceeds capacity, performance degrades, tasks are shed and error rates rise; when workload is very low, vigilance and monitoring suffer.

The condition in which task demands exceed the crew's capacity to process them, so important items are missed or delayed. It is managed by prioritising, delegating, automating and reducing non-essential activity.

Reduced monitoring of automated systems because they are trusted to perform reliably. It leads to late detection of mode changes or failures, so crews must verify what the automation is actually doing.

A mismatch between the crew's understanding of the automation's active mode and its actual mode. It produces unexpected aircraft behaviour, and prevention relies on clear mode awareness and cross-checking.

A physiological state of reduced mental or physical performance caused by sleep loss, extended wakefulness, circadian disruption or workload. It impairs reaction time, attention and judgement, and cannot be overcome by willpower.

The roughly 24-hour internal cycle that regulates sleepiness, alertness and body temperature. It is synchronised mainly by daylight, and flying across time zones or at night desynchronises it, causing performance troughs.

The accumulated shortfall between sleep needed and sleep obtained. It builds over consecutive restricted nights, degrades performance progressively, and is repaid only by adequate recovery sleep.

A temporary disruption of sleep and alertness caused by rapid travel across time zones, where the body clock is out of step with local time. Eastward travel is usually harder to adapt to.

The general level of physiological and psychological activation. Performance is best at moderate arousal; too little produces boredom and inattention, while too much produces narrowed attention, tremor and degraded judgement.

The body's response to demands it perceives as exceeding its resources. Short-term stress can sharpen performance, but prolonged or extreme stress impairs memory, judgement and communication and affects health.

A formal, organisation-wide framework for identifying hazards, assessing risk and assuring safety performance through policy, reporting and continuous improvement. It complements individual skills with systemic defences.