ATPL 040 Human Performance cheat sheet

Human factors is the study of the interrelationships between humans, the tools they use, and the environment in which they live and work; it applies to the whole aviation system, not only to pilots.

SHELL model: Software (rules, SOPs, checklists), Hardware (aircraft, displays), Environment (physical and organisational), and Liveware (people). The central Liveware is the focus; mismatches at any interface create error.

Liveware-Liveware interface (crew interaction) is the most error-prone in the SHELL model because it is the least predictable and least standardised.

Reason's Swiss cheese model: accidents occur when holes in successive defensive layers line up; holes are active failures (front-line) and latent conditions (management, design, training).

Error types in Reason's model: slips (correct intention, wrong execution), lapses (forgotten action), mistakes (wrong intention), violations (deliberate deviation).

Safety culture components: informed, reporting, just, flexible, and learning culture; a just culture distinguishes honest error from reckless or intentional unsafe behaviour.

ICAO Doc 9859 (Safety Management Manual) frames human factors within Safety Management Systems; Annex 13 accident investigation and Annex 19 safety management underpin this.

History: aircraft accidents attributable to human error are commonly cited as roughly 70-80% of the total; human factors training (CRM) originated after the 1970s accident studies.

Atmospheric composition is approximately 78% nitrogen, 21% oxygen, 1% other gases; Dalton's law states total pressure equals the sum of partial pressures, so oxygen partial pressure falls with altitude.

Alveolar oxygen partial pressure determines haemoglobin saturation; at 10,000 ft (about 3,000 m) saturation is about 90%, and at 14,000 ft (about 4,300 m) about 80-85% without supplemental oxygen.

Time of useful consciousness without oxygen: roughly 20-30 min at 18,000 ft, 1-3 min at 25,000 ft, 30-60 s at 30,000 ft, and 15-20 s at 40,000 ft.

Hypoxia symptoms: euphoria, impaired judgement, cyanosis, headache, visual disturbance, tingling, and loss of consciousness; the first sign is often a loss of self-awareness of the deficit.

Hyperventilation causes hypocapnia (low CO2), leading to cerebral vasoconstriction, dizziness, tingling of extremities, and tetany; treatment is to slow breathing or use a bag, not oxygen.

Ear barotrauma: the eustachian tube equalises middle-ear pressure; descent (external pressure rising) is harder to equalise than ascent; Valsalva opens the tube.

Spatial disorientation arises when vestibular and visual cues conflict; the semicircular canals detect angular acceleration only, not steady rotation, so a prolonged turn may feel level.

Blood functions: transport of oxygen (haemoglobin), CO2, nutrients, hormones, and heat, plus defence (white cells) and clotting (platelets); normal haemoglobin is about 13-18 g/dL.

Information processing stages: sensation, perception, attention, decision-making, response; each stage takes time and can be overloaded.

Attention is limited; selective attention filters stimuli, divided attention splits capacity, and vigilance decrements occur after about 30 min of monotonous monitoring.

Perception is based on expectation; expectancy bias and 'expectation error' cause pilots to see or hear what they expect rather than what is present.

Memory: sensory store (fraction of a second), short-term/working memory (about 7 ± 2 items, roughly 20-30 s), long-term memory (unlimited, requires rehearsal or meaningful encoding).

Human error reliability: error is normal and unavoidable; performance variability is not itself a failure, and error rates increase under stress, fatigue, and high workload.

Decision-making models: OODA (observe, orient, decide, act), DECIDE, and recognition-primed decision making (experienced operators match patterns to familiar situations).

Judgement and risk: risk assessment is influenced by optimism bias, hazardous attitudes (anti-authority, impulsivity, invulnerability, machismo, resignation), and the normalisation of deviance.

Learning: reinforcement and feedback improve retention; overlearning of emergency procedures improves recall under stress; transfer of training is positive when conditions match.

Stress: the non-specific response of the body to any demand; the Yerkes-Dodson curve shows performance peaks at moderate arousal and declines at very low or very high arousal.

Stressors include environmental (noise, vibration, temperature, hypoxia), physiological (fatigue, illness), psychological (workload, interpersonal), and organisational (roster, job security).

Fatigue types: acute (short-term, recoverable with sleep), chronic (cumulative), and circadian (time-of-day); fatigue impairs vigilance, reaction time, and decision-making before the person notices.

Circadian rhythm: the body clock has a period slightly longer than 24 h; the nadir of alertness is around 03:00-05:00 and a secondary dip around 13:00-15:00 local time.

Sleep: adults need about 7-9 h; sleep debt accumulates and is not fully repaid by a single long sleep; sleep inertia follows awakening, especially from deep sleep or at the circadian low.

Shift work: rotating shifts, especially backward rotation (day to night), disrupt circadian rhythm; eastward time-zone travel causes more disruption than westward.

Workload: mental workload is the ratio of task demand to capacity; overload causes errors and omissions, underload causes boredom, complacency, and vigilance failure.

Automation: increased automation shifts the role from operator to monitor, causing complacency, skill degradation, and automation-induced workload peaks at transition points.

Decompression sickness (DCS): nitrogen dissolved in tissues at higher pressure comes out of solution on decompression; symptoms include joint pain (bends), skin mottling, respiratory (chokes) and neurological effects; treatment is descent, 100% oxygen, and recompression.

Barotrauma: gas in body cavities expands with altitude (Boyle's law, P·V = constant); trapped gas in ears, sinuses, gut, or teeth causes pain, and descent causes the reverse squeeze.

Vision in flight: rods (peripheral, night, low acuity) vs cones (central, colour, high acuity); the fovea has a blind spot at the optic disc; dark adaptation takes 20-30 min and is destroyed by bright light.

Night vision: use off-centre viewing (about 10-15° from the object) because the fovea is poor in low light; avoid smoking and high cabin altitude because both reduce oxygen supply to the retina.

Acceleration: G forces cause blood to pool, leading to grey-out (peripheral vision loss), blackout, and G-LOC; anti-G straining manoeuvre and anti-G suits increase tolerance; negative G causes red-out.

Motion sickness: conflict between vestibular (semicircular canals, otoliths) and visual cues; symptoms include nausea, pallor, and sweating; habituation and looking at a distant fixed point help.

Toxic hazards: carbon monoxide (from heaters, exhaust) binds haemoglobin about 200-250 times more strongly than oxygen; cabin ozone and contaminated bleed air are other hazards; hypoxia symptoms may be insidious.

Radiation: cosmic ionising radiation increases with altitude and latitude; aircrew are occupationally exposed and monitored; UV exposure is higher at altitude and can damage eyes and skin.

Communication: the sender encodes, the receiver decodes, and feedback confirms; barriers include noise, jargon, expectation bias, and authority gradient.

Crew coordination: briefing, cross-checking, monitoring, and challenge-and-response standard calls reduce error; effective monitoring requires active, not passive, attention.

Teamwork: shared mental model, clear roles, mutual support, and closed-loop communication (read-back) are core CRM skills; assertiveness must be balanced with respect for authority.

Leadership: the captain sets the tone; autocratic leadership suppresses input, while laissez-faire leadership loses control; situational leadership adapts style to the phase of flight.

Conflict: task conflict can improve decisions, but relationship conflict degrades teamwork; resolution uses active listening, 'I' statements, and focus on the problem, not the person.

Situational awareness: three levels (perception of elements, comprehension of meaning, projection of future state); loss is commonly from fixation, ambiguity, or failure to monitor.

Automation monitoring: mode awareness, FMA (flight mode annunciator) scanning, and understanding what the automation is doing are essential; automation surprises arise from mode confusion.

Human-machine interface: design should follow consistency, standardisation, and clear feedback; poorly designed displays cause capture errors and increased workload.

Flight deck design: controls and displays should be logical, standardised, and compatible with human capabilities; warning systems must be prioritised (e.g., master caution vs warning) and unambiguous.

Standard operating procedures (SOPs) provide a common baseline for crew coordination; deviation from SOPs is a common precursor in accident reports.

Checklists: do-list vs read-do; challenge-response format; the 'killer items' should be at the top; checklist complacency and rushed performance reduce their effectiveness.

Threat and Error Management (TEM): threats (external events), errors (crew actions), and undesired aircraft states; countermeasures are avoidance, trapping, and mitigation.

Safety reporting: confidential, non-punitive reporting increases the number of reports and reveals latent hazards; reporting systems include mandatory and voluntary schemes.

Just culture: distinguishes human error (console), at-risk behaviour (coach), and reckless behaviour (punish); it supports learning while maintaining accountability.

Safety management: hazard identification, risk assessment, and risk mitigation; safety performance indicators (SPIs) and safety performance targets (SPTs) measure effectiveness.

Crew resource management (CRM): training in communication, leadership, decision-making, and workload management; initial and recurrent training are required by regulation (e.g., EASA, FAA).