PPL Human Performance and Limitations key terms

A condition in which body tissues receive insufficient oxygen. In aviation it most often results from high altitude, and it impairs vision, judgement and motor control before the person notices anything is wrong.

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

A gradual loss of cabin pressure that produces no sudden noise or rush of air. Oxygen starvation develops insidiously and symptoms such as euphoria or tingling may be mistaken for fatigue, so pressure checks and oxygen discipline matter.

Breathing faster or deeper than metabolic need, which lowers blood carbon dioxide. Symptoms resemble hypoxia, including dizziness, tingling and confusion, so the two must be distinguished carefully in flight.

Injury to gas-filled body spaces caused by pressure change it cannot equalise. The ears, sinuses, teeth and gut are typical sites, and pain during descent is the usual warning sign.

Failure to equalise pressure across the eardrum, usually on descent, causing pain, muffled hearing and sometimes vertigo. It is more likely with a cold or blocked Eustachian tube and may not resolve on the ground.

Nitrogen bubbles forming in tissues when ambient pressure falls too quickly after exposure to higher pressure. In aviation it can follow unpressurised flight or rapid decompression; joint pain and skin or nerve symptoms are typical.

A mismatch between the aircraft's actual attitude or motion and the pilot's perception of it. It arises because the balance organs cannot separate gravity from acceleration, and it can persist even with clear visual cues.

The inner-ear organs that sense rotation and linear acceleration. The semicircular canals respond to turning and the otoliths to gravity and acceleration, but neither can reliably separate gravity from sustained acceleration.

A false sensation of pitch caused by linear acceleration or deceleration. Strong acceleration in level flight feels like climbing, prompting an unnecessary nose-down input, while deceleration feels like a descent.

A false sensation of banking that appears after a gradual, unnoticed roll away from level flight. The pilot perceives the aircraft as banked and may correct in the wrong direction when returning to straight flight.

A spiral dive that develops when a pilot in a prolonged coordinated turn without visual reference fails to perceive the bank. The resulting sensation of turning the other way encourages a steeper turn rather than recovery.

A false attitude impression created by physical forces on the body, such as seat pressure during acceleration or a sudden jolt. The feeling of being pushed into the seat may be read as a climb or a bank.

A false sensation of rotation that continues after a sustained turn ends, or that fails to register during a slow turn entry. It commonly leads to a misjudged roll-out or to an unrecognised bank.

A visual illusion on a dark night approach over unlit terrain, where the only visible reference is the runway. The pilot tends to fly too low and too far down the approach path.

A misleading perception of the runway or environment produced by terrain, lighting, rain or runway slope. It can cause an approach that is too high, too low, too fast or too slow if instruments are not cross-checked.

The tendency of the eyes to relax to a resting focus of roughly one metre when viewing a featureless field such as sky or haze. Distant traffic can then go unseen until it is dangerously close.

A deliberate technique of moving the gaze in short, regular steps across sectors of the sky and pausing at each point. It works because the eye sees detail only in a small central area and adapts poorly to a fixed stare.

An accurate, up-to-date understanding of what is happening around the aircraft and what is likely to happen next. It has three levels: perceiving cues, comprehending their meaning and projecting future states.

A framework in which crews anticipate external threats, trap or manage errors before they affect the flight, and avoid undesired aircraft states. It treats error as normal and focuses on resilience rather than blame.

A sequence of linked mistakes and omissions that together produce an accident, where breaking any single link could prevent the outcome. It explains why accidents rarely stem from one isolated failure.

A way of picturing safety as layers of defence, each with holes representing weaknesses. An accident occurs only when holes in successive layers line up, so defences should be independent and redundant.

An organisational approach that distinguishes human error, which should be openly reported, from reckless or intentional violation, which warrants sanction. It encourages learning without removing individual accountability.

A structured set of policies, processes and feedback loops an organisation uses to identify hazards, assess risk and monitor the effectiveness of mitigations. It relies on reporting, data analysis and continuous improvement.

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

The skill of stating a concern clearly and respectfully, and persisting until it is acknowledged, while remaining open to other views. It balances deference to authority against the duty to speak up.

A crew relationship in which the captain's authority is so dominant that other members withhold information or concerns. It suppresses challenge and increases the chance that important cues go unspoken.

A short, planned exchange before a flight phase that sets out intentions, threats, division of tasks and contingencies. It builds shared expectations and gives crew members a basis for challenging deviations.

The mental and physical effort required to perform tasks in a given time. It rises with task demand and can become excessive or, at the other extreme, so low that vigilance drops.

The general level of alertness and physiological activation. Performance improves as arousal rises from low levels but degrades when arousal becomes too high, a relationship often shown as an inverted U.

A response to demands perceived as exceeding one's ability to cope. Short-term stress can sharpen attention, but prolonged stress narrows focus, disturbs sleep and degrades judgement and memory.

A state of reduced performance capacity caused by sustained effort, inadequate sleep or disrupted body rhythm. It slows reactions, increases variability and impairs the ability to notice one's own deterioration.

The roughly 24-hour internal cycle that governs sleepiness, body temperature and alertness. Flying across time zones or at night can misalign it, producing low alertness at times the pilot expects to be sharp.

The tendency to seek, notice and remember information that supports an existing belief while discounting contrary evidence. In flight it can keep a pilot committed to a failing plan or an incorrect diagnosis.

The tendency to keep following an original plan despite changing conditions that call for revision. It contributes to pressing on into deteriorating weather or continuing an unstable approach.

The process of gathering information, weighing options against goals and risk, choosing a course of action and reviewing the result. In aviation it is often compressed by time pressure and incomplete information.

An unintended action or omission by a person that deviates from intention or expectation. It is normal and inevitable, so safety work aims to contain its consequences rather than eliminate it.

A model showing that performance depends on fit between the software, hardware, environment and liveware, with people at the centre. Mismatches at these interfaces are where errors and accidents tend to arise.