Part-66 Module 9 cheat sheet

Human factors is the study of how people interact with equipment, procedures and the environment; its aim is safe and efficient performance.

ICAO defines human factors as the optimisation of human performance within the aviation system through the systematic application of human sciences.

SHELL model: Liveware (people) interacts with Software (procedures), Hardware (equipment), Environment and other Liveware; mismatches at these interfaces cause error.

PEAR model: People, Environment, Actions and Resources are used to analyse maintenance human factors.

Reason's model: organisational factors and supervision create latent conditions that combine with active unsafe acts to breach defences.

The Dirty Dozen precursors are fatigue, complacency, pressure, stress, distraction, lack of communication, lack of teamwork, lack of resources, lack of assertiveness, lack of knowledge, norms and awareness.

Human error is implicated in roughly 70–80% of aviation accidents; maintenance and inspection errors are a significant contributor.

MEDA (Maintenance Error Decision Aid) is a structured tool for investigating maintenance errors and identifying organisational causes.

Eye: cones in the fovea give high-acuity colour vision in daylight; rods in the periphery give low-light, motion-sensitive vision.

Dark adaptation takes about 20–30 minutes; exposure to bright white light resets it.

Hearing range is about 20 Hz–20 kHz; speech is mainly 500–3000 Hz and the ear is most sensitive at 2–4 kHz.

Memory: sensory store under 1 second; short-term/working memory 7 ± 2 items for 15–30 seconds; long-term memory has large capacity.

Information processing follows perception → decision → response; channel capacity is limited, and overload causes omission or error.

Attention is selective, divided and sustained; vigilance on monotonous tasks declines after about 20–30 minutes.

Arousal and performance follow an inverted-U; both underload and overload degrade performance.

Circadian rhythm is about 24.2 hours; alertness minima occur around 03:00–05:00 and 15:00–17:00 body time.

Hypoxia: above about 10,000 ft performance falls; time of useful consciousness at FL350 is about 30–60 seconds.

Groups develop norms; conformity can make individuals accept a group judgement that conflicts with their own.

Groupthink symptoms include illusion of invulnerability, self-censorship and direct pressure on dissenters.

Authority gradient: a steep gradient discourages junior challenge; a flat gradient can blur command; assertiveness balances both.

CRM trains communication, leadership, teamwork, decision-making and situation awareness to use all resources.

Synergy means a coordinated team can outperform the sum of individual efforts.

Peer pressure can normalise unsafe shortcuts, but a strong safety culture can make safe behaviour the norm.

Role ambiguity and unclear responsibilities increase duplication, omission and error.

Social loafing: individuals may exert less effort in a group when their contribution is not identifiable.

Cultural differences in deference, gesture and humour can distort communication; understanding should be checked explicitly.

Stress is the response to demands; the inverted-U shows moderate arousal aids simple tasks but impairs complex ones.

Acute fatigue causes slowed reactions and lapses; chronic fatigue causes apathy, irritability and cumulative sleep debt.

Adults generally need 7–9 hours' sleep; sleep debt accumulates and a 20-minute nap can temporarily restore alertness.

Alcohol impairs judgement, vigilance and psychomotor skills; hangover effects persist after blood alcohol falls.

Sedatives, antihistamines and some prescription drugs impair performance; self-medication is a known aviation risk.

Motivation affects effort; over-motivation can narrow attention and impair fine control.

Dehydration of about 2% of body mass can impair cognition and physical performance.

Illness and pain distract attention and reduce capacity; fitness improves recovery from physical demand.

Shift work disrupts circadian rhythm and sleep, increasing fatigue and error risk.

Noise exposure: lower action level 80 dB(A), upper action level 85 dB(A), exposure limit 87 dB(A) for 8 hours; a 3 dB increase doubles the dose.

Hearing protection must reduce exposure below the limits; communication and warning signals must still be audible.

Illuminance: about 300–500 lux for normal work, 750 lux or more for detailed inspection; glare and shadows impair vision.

Thermal comfort: about 20–24 °C and 30–60% relative humidity; heat causes dehydration and cold impairs dexterity.

Hand-arm vibration can cause white finger; whole-body vibration impairs vision, comfort and balance.

Air quality: carbon monoxide, carbon dioxide, fumes and vapours must be controlled by ventilation and monitoring.

Altitude reduces oxygen partial pressure; above 10,000 ft hypoxia degrades night vision and judgement first.

Motion sickness results from mismatch between visual, vestibular and proprioceptive signals.

Physical work includes lifting, carrying, pushing and pulling; energy demand depends on load, posture and duration.

Ergonomics fits the task to the person: work height near elbow level, reach within the easy zone, neutral wrist and back.

Manual handling rule: keep the load close, back straight, knees bent, avoid twisting; use mechanical aids where possible.

Repetitive movement and sustained posture cause work-related upper-limb disorders.

Task analysis breaks a task into steps and identifies hazards, inputs, decisions and error-likely points.

Vigilance decrement: detection of rare signals falls after 20–30 minutes of monitoring.

Complacency is most likely in highly routine or highly automated tasks with few apparent threats.

Shift handover should be structured, face-to-face and written, covering status, outstanding work and hazards.

Workload can be measured by subjective rating, task performance or physiological measures.

Communication requires sender, message, medium, receiver and feedback; physical, semantic and psychological noise distort it.

Written communication suits complex or procedural information; verbal is faster but more liable to distortion.

Standard phraseology reduces ambiguity; slang, abbreviations and non-standard words increase misunderstanding.

Assertiveness is stating a concern clearly with facts and a desired outcome, even to senior personnel.

Active listening includes paraphrasing and confirming; filters such as expectation and prejudice cause mishearing.

Pre-task briefings should cover task, roles, hazards, resources and contingencies.

Language and cultural differences increase risk; use plain words, check-back and avoid humour or idiom.

Communication breakdown is a recurring factor in maintenance and operational accidents.

Error is unintentional; a violation is a deliberate deviation from rules or procedures.

Skill-based errors are slips (attention failure) and lapses (memory failure); they occur in routine, practised tasks.

Rule-based and knowledge-based mistakes are intention errors; knowledge-based errors occur when the situation is unfamiliar.

Indicative error rates: skill-based about 1 in 1,000; rule-based about 1 in 100; knowledge-based about 1 in 10.

Reason's Swiss cheese model: latent organisational conditions and active failures align with holes in defences.

Latent failures are management decisions and conditions; active failures are errors and violations at the sharp end.

Error management has three lines: reduce error, capture error, and tolerate or contain its consequences.

Violation types: routine (normalised), situational (pressure), exceptional (emergency) and sabotage.

A just culture distinguishes human error from reckless or intentional unsafe behaviour.

PPE is the last line of defence; it must be suitable, maintained, correctly fitted and used.

FOD control: clean as you go, tool control, accountability and inspection before closing.

COSHH requires risk assessment, prevention or control of exposure, monitoring and health surveillance.

Electrical work: isolate, lock off, prove dead and use suitable PPE.

Hydraulic fluid can irritate skin and cause pressure injection injury; use gloves and eye protection.

Fire: use the correct extinguisher class; water for solids, foam for liquids, CO2 for electrical fires.

Working at height requires guardrails, fall arrest and inspection of equipment.

Confined spaces require atmosphere testing, ventilation, rescue arrangements and a permit.

Noise, dust and fumes in the workplace require monitoring and control at source.