ATPL Human Factors cheat sheet

Human factors is the study of the interrelationships among humans, the equipment they use, the environments in which they work, and the tasks they perform; its goal is safe, efficient performance.

The SHEL model (Edwards) depicts Software, Hardware, Environment and Liveware; the central Liveware is the human, and the liveware-liveware interface (crew interaction) is the most critical and least predictable.

ICAO uses the SHELL model, adding a second Liveware to emphasise that people interact with other people as well as with machines and procedures.

The 'dirty dozen' lists twelve frequent human-factor precursors to maintenance and operational error: lack of communication, complacency, lack of knowledge, distraction, lack of teamwork, fatigue, lack of resources, pressure, lack of assertiveness, stress, lack of awareness, and norms.

Reason's Swiss-cheese model: accidents occur when holes in successive defensive layers (organisational, supervisory, preconditions, unsafe acts) momentarily align.

The error chain concept holds that accidents rarely result from a single act but from a sequence of linked events; breaking any link prevents the outcome.

Safety management shifts from reactive (post-accident) to proactive and predictive approaches using hazard identification, risk assessment and safety assurance.

Physiological and psychological limitations are normal human characteristics, not personal failings; design and training should accommodate them rather than blame individuals.

Dalton's law: total pressure is the sum of partial pressures; at altitude, reduced ambient pressure lowers alveolar oxygen partial pressure and causes hypoxia.

Henry's law: gas dissolved in a liquid is proportional to its partial pressure; rapid decompression releases dissolved nitrogen, causing decompression sickness.

Time of useful consciousness after rapid decompression is roughly 15-20 s at FL 400, 30-60 s at FL 350, and 2-3 min at FL 300.

Hypoxia types: hypoxic (reduced oxygen availability), hypemic (anaemia, CO, blood loss), stagnant (circulatory), histotoxic (cell poisoning, e.g. alcohol, cyanide).

Hyperventilation lowers arterial CO2, causing dizziness, tingling and cramps; treatment is controlled breathing and, if in doubt with hypoxia, oxygen.

Spatial disorientation arises when vestibular and visual cues conflict; the somatogravic illusion during acceleration mimics a nose-up pitch, and the leans follow a slow bank.

Barotrauma of the ear and sinuses results from pressure differences across blocked cavities; equalisation via Valsalva or Toynbee manoeuvre is required during descent.

Circadian rhythm disruption and sleep loss degrade performance; fatigue is best managed by adequate pre-flight rest, controlled napping and limiting continuous duty.

Motivation can be intrinsic (task interest) or extrinsic (rewards); excessive arousal from high motivation degrades fine motor skills and narrows attention.

Yerkes-Dodson law: performance peaks at moderate arousal; the optimal level is lower for complex tasks and higher for simple ones.

Maslow's hierarchy orders needs from physiological and safety through belonging, esteem and self-actualisation; unmet lower needs dominate attention.

Attitudes in the 'hazardous attitudes' set include anti-authority, impulsivity, invulnerability, machismo and resignation; each has a named antidote.

Personality traits such as high risk tolerance, impulsivity or low self-confidence influence decision-making and should be recognised by the pilot.

Stress can be acute, chronic or traumatic; moderate stress improves performance, but prolonged stress causes fixation, narrowing of attention and poor judgement.

Defence mechanisms such as denial, projection and rationalisation can hide a developing problem from the pilot and the crew.

Learning is most effective when material is meaningful, reinforced, spaced and actively practised; overlearning improves retention of emergency procedures.

Errors are classified as slips (correct intention, wrong execution), lapses (memory failure), mistakes (wrong intention or rule) and violations (deliberate deviation).

Reason distinguishes skill-based, rule-based and knowledge-based levels; most errors occur at the skill-based level, while knowledge-based errors are more likely under novel, high-stress conditions.

Active failures are unsafe acts by front-line operators; latent conditions are organisational or design weaknesses that lie dormant until triggered.

Violations may be routine (accepted practice), situational (pressured by circumstances) or exceptional (rare, extreme); routine violations are a symptom of weak safety culture.

Human reliability assessment estimates error probability; performance-shaping factors such as fatigue, time pressure and poor communication increase it.

Error management has three layers: error avoidance (training, design), error trapping (checklists, cross-checks) and error tolerance (redundancy, recovery).

Just culture distinguishes human error (consoled), at-risk behaviour (coached) and reckless behaviour (sanctioned), encouraging reporting without fear.

Error rates for well-practised tasks are low; reliability improves with feedback, standardisation and independent verification.

Arousal and workload follow an inverted-U relationship: too low (underload) causes boredom and inattention, too high (overload) causes errors and tunnel vision.

Workload is the proportion of mental resources demanded by a task; when demand exceeds capacity, task shedding and priority errors occur.

Overload symptoms include narrowing of attention, loss of situational awareness, omission of secondary tasks and increased reaction time.

Underload in highly automated cockpits produces complacency, vigilance decrement and 'automation complacency' during long cruise phases.

Vigilance decrement means detection of rare signals declines over time, especially in monotonous monitoring tasks.

Task management techniques include prioritisation, delegation, and 'aviate, navigate, communicate' sequencing.

Automation can reduce workload in high-demand phases but increase it during mode changes and failures; automation surprise is a known risk.

Optimal workload is achieved by balancing task demands against crew resources, including automation, and by ensuring adequate rest.

Information processing stages: sensation, perception, attention, decision-making, response; each stage can introduce error.

Attention is limited; selective attention filters relevant cues, while divided attention is degraded by high workload.

Short-term memory holds about 7±2 items for 15-30 s; long-term memory has large capacity but requires rehearsal and meaningful encoding.

Sensory memory stores visual (iconic) and auditory (echoic) information for a fraction of a second to a few seconds.

Perception is influenced by expectation, experience and motivation; expectation bias can cause misreading of instruments.

Decision-making models include the DECIDE model (Detect, Estimate, Choose, Identify, Do, Evaluate) and the OODA loop (Observe, Orient, Decide, Act).

Heuristics such as availability, representativeness and anchoring can speed decisions but introduce systematic bias.

Situation awareness has three levels: perception of elements, comprehension of their meaning, and projection of future status.

CRM uses all available resources - people, equipment, information - to achieve safe and efficient flight; it targets communication, leadership, teamwork and decision-making.

Effective teams share a common goal, clear roles, mutual trust and closed-loop communication with confirmation of receipt.

Leadership should be situation-dependent; the captain retains authority but encourages input and flattening of the hierarchy when appropriate.

Assertiveness is the ability to state a concern clearly and persistently until it is acknowledged, without aggression.

Briefings set expectations, allocate tasks and establish an open communication climate; debriefings consolidate learning.

Conflict should be resolved by focusing on facts and the task, not personalities; unresolved conflict degrades crew performance.

Crew monitoring requires active cross-checking of actions and callouts; passive monitoring is a common precursor to error.

CRM training is recurrent and includes case studies, role-play and line-oriented flight training to reinforce non-technical skills.

Standard phraseology reduces ambiguity; non-standard phrasing increases misunderstanding risk, especially under high workload.

Closed-loop communication: sender transmits, receiver reads back, sender confirms; this confirms accurate reception.

Communication barriers include noise, fatigue, language proficiency, cultural differences and authority gradients.

The authority gradient should be low enough for juniors to speak up yet clear enough for decisive command when needed.

Effective callouts are specific, timely and directed; vague or delayed callouts allow errors to propagate.

Listening is active: the receiver should acknowledge, clarify and confirm understanding rather than assume.

Handover and briefings should be structured (e.g. situation, background, assessment, recommendation) to ensure complete information transfer.

Non-verbal cues and tone matter; sarcasm or dismissive responses suppress future reporting.

Human error contributes to the majority of aviation accidents, often through breakdowns in communication, decision-making or monitoring.

Safety occurrence reporting systems (mandatory and voluntary) capture hazards; confidentiality encourages reporting of near-misses.

Threat and Error Management (TEM) identifies threats, anticipates errors and manages undesired aircraft states.

Line Operations Safety Audit (LOSA) observes normal operations to identify threats and errors and to measure CRM effectiveness.

Safety culture components: reporting culture, just culture, flexible culture and learning culture.

Risk assessment uses likelihood and severity matrices; mitigation reduces risk to an acceptable level (ALARP).

Flight data monitoring and incident analysis reveal latent conditions and trends before accidents occur.

Fatigue risk management systems and duty-time limitations are regulatory tools to control human-performance risk.