PPL Human Performance and Limitations cheat sheet

Human factors = the study of how people interact with equipment, procedures and the environment; the SHELL model maps Software, Hardware, Environment and Liveware, with the central Liveware (the human) interacting with each of the other four.

The 'dirty dozen' concept groups recurrent human-error precursors (e.g. fatigue, complacency, distraction, pressure, lack of assertiveness); each is a symptom to be managed, not a root cause in itself.

Reason's model: unsafe acts (slips, lapses, mistakes, violations) are the last link; latent conditions are decisions/design flaws resident in the system long before the error.

Hypoxia types: hypoxic (reduced alveolar O2, e.g. altitude), hypemic (reduced O2-carrying capacity, e.g. anaemia, CO), stagnant (poor circulation), histotoxic (cells cannot use O2, e.g. alcohol, cyanide).

Time of useful consciousness at cabin altitude: roughly 15-30 s at FL 400, 30-60 s at FL 350, 2-5 min at FL 300, 5-10 min at FL 250; the range reflects individual variation and activity level.

Barotrauma: Boyle's law (P x V = constant) means trapped gas expands on ascent and contracts on descent; the middle ear, sinuses and gut are the usual sites, and the eardrum is the limiting factor in descent.

Decompression sickness risk rises with altitude, duration, repeated exposure and physical activity after exposure; divers must observe surface intervals before flying (e.g. 12-24 h after non-decompression dives).

G-induced loss of consciousness (G-LOC) results from cerebral hypoperfusion; the AGSM (tensing legs/abdomen, L-1/M-1 manoeuvre, breathing in short syllables) raises tolerance, and anti-G suits add protection.

Carbon monoxide binds haemoglobin about 200-250 times more strongly than oxygen, producing hypemic hypoxia; symptoms (headache, confusion) are insidious and the pulse oximeter may read falsely normal.

Ear blocks on descent: use Valsalva (gentle nose pinch + blow), Toynbee (swallow while pinching), or yawning; if a cold or congestion prevents equalisation, do not fly or do not continue descending.

Sinus barotrauma presents as pain over the affected sinus, often with tooth or facial pain; it is more likely with upper respiratory infection and can rupture into the nasal cavity on descent.

Hypoxia signs: euphoria, poor judgement, cyanosis, tingling, visual dimming; the first symptom is often loss of self-awareness, so treat any unexplained deterioration as hypoxia and use 100% oxygen.

Hyperventilation and hypoxia can look identical; the operational rule is to assume hypoxia first, put on 100% oxygen and control breathing rate, not to diagnose at altitude.

Vision: scotopic (night) vision depends on rods, which are concentrated in the periphery and poor at the fovea; use off-centre viewing (about 10-15 degrees) at night and allow 30 minutes for dark adaptation.

Night myopia and empty-field myopia occur in low light with no visual reference; focus on a distant object periodically to break the accommodation.

Cabin air is dry (relative humidity often under 20%); dehydration, alcohol and caffeine worsen fatigue and reduce tolerance to hypoxia; water intake is the practical countermeasure.

Circadian rhythm: the body clock is entrained by light; eastward travel (phase advance) is generally harder than westward, and short layovers prevent full adaptation.

Fatigue is cumulative: sleep debt cannot be repaid by a single long sleep; controlled rest on the flight deck (if permitted) is short (about 20-45 min) to avoid sleep inertia on waking.

Heat and cold: heat causes dehydration and reduced G tolerance; cold causes shivering and impaired dexterity; both degrade performance before the person notices.

Attention is limited: vigilance (sustained attention) decays within about 30 minutes on monotonous tasks; the classic vigilance decrement is a normal human limit, not a discipline problem.

Selective attention: expectancies guide what is perceived; unexpected but salient events (e.g. a runway incursion, a gear-up warning) can be missed - this is inattentional blindness.

Working memory holds roughly 7 +/- 2 items for seconds; use written notes, checklists and clearances read-back to offload it.

Stress: performance follows an inverted-U (Yerkes-Dodson); moderate arousal helps, but high arousal narrows attention and increases errors of omission.

Habit and skill-based behaviour are fast and error-resistant but are also where capture errors occur; the checklist and cross-check are designed to interrupt automatic routines.

Motivation and personality affect risk-taking: high sensation-seeking and low self-control correlate with more hazardous attitudes in aviation.

Perception is constructive: expectation, motivation and emotion shape what is seen; a pilot who expects a particular runway may 'see' it despite a different one being present.

Learning: distributed practice beats massed practice for retention; feedback and active recall improve skill retention; interference from similar tasks causes confusion under stress.

The semicircular canals detect angular acceleration, not sustained rotation; after about 10-20 s of constant rotation the endolymph catches up and the sensation of turning fades (adaptation).

The otolith organs detect linear acceleration and gravity by the same mechanism; they cannot distinguish a sustained acceleration from a change in orientation (the somatogravic illusion).

Somatogravic illusion: during strong linear acceleration (take-off), the pilot may feel a nose-up attitude and push forward; during deceleration (go-around, airbrake), a nose-down sensation.

Somatogyral illusion: after a sustained turn, a sudden return to level flight feels like a turn in the opposite direction, prompting an incorrect correction.

The leans: a slow roll below the canal threshold is not detected; the pilot 'feels' level while banked and may correct in the wrong direction.

Coriolis illusion: moving the head during a sustained turn produces tumbling sensations; avoid head movements during prolonged turns and recover using instruments.

Visual illusions: black-hole effect (no ground reference on approach leads to a low approach), runway width illusion (narrow runway appears farther, causing a low approach), and slope illusion (upsloping runway appears closer/higher).

Vestibular and visual cues conflict in IMC; the reliable response is to trust the instruments and use a defined instrument scan, not to 'feel' the attitude.

Disorientation countermeasures: instrument proficiency, avoiding abrupt head movements, maintaining a good visual horizon, and using the autopilot to reduce workload in IMC.

Decision-making models: the DECIDE model (Detect, Estimate, Choose, Identify, Do, Evaluate) and the FOR-DEC loop (Facts, Options, Risks, Decision, Execute, Check) provide a structured cycle rather than a single choice.

Recognition-primed decision making: experts match a situation to a known pattern and act; this is fast but can fail when the situation is novel or the pattern is misread.

Confirmation bias: people seek and weight information that supports an existing hypothesis; counter by actively seeking disconfirming evidence.

Plan continuation bias (get-home-itis): crews continue with a plan despite accumulating evidence against it; set explicit decision gates (e.g. fuel, weather minima) before the flight.

Error management: errors are inevitable; defences are trapping (checklists, cross-checks, read-backs), mitigating (recovery, redundancy) and reducing consequences.

Slips are attention/monitoring failures (right intention, wrong execution); mistakes are planning/intention errors (wrong plan); lapses are memory failures; violations are deliberate deviations from rules.

Automation: mode confusion and automation complacency occur when pilots lose track of what the automation is doing; keep 'what is it doing, why is it doing that, what will it do next' as a verbal check.

Decision-making under time pressure: prioritise aviate, navigate, communicate; the first action should stabilise the aircraft before diagnosis.

Communication loop: sender encodes, receiver decodes, feedback confirms; a read-back is the required feedback for clearances and safety-critical instructions.

Standard phraseology reduces ambiguity; non-standard phrases and slang increase the chance of misunderstanding, especially across languages and cultures.

Assertiveness: the PACE model (Probe, Alert, Challenge, Emergency) escalates a concern when the first statement is not heard; it is a graded tool, not a single challenge.

Authority gradient: steep gradients suppress junior input; flattened gradients can cause indecision; the captain should invite challenge and state intent clearly.

Situational awareness has three levels: perception of elements, comprehension of their meaning, and projection of future status; loss of SA is a leading precursor to incidents.

Briefings set shared expectations; an effective brief covers threats, the plan, roles and 'what if' contingencies, and is short enough to be used.

Fatigue, stress and workload degrade communication first: shorter phrases, missed read-backs and reduced monitoring are early signs.

Cultural factors (power distance, individualism, uncertainty avoidance) affect how crews challenge and report; CRM training must address these explicitly.

Leadership: the captain sets the tone; a leader who admits uncertainty and invites input improves crew performance more than one who asserts authority.

Safety is the state in which risk is acceptable; safety management is the organisational process of identifying hazards, assessing risk and mitigating it (SMS: safety policy, risk management, assurance, promotion).

The Swiss cheese model: defences have holes; an accident requires the holes to align; the goal is to add and strengthen defences rather than blame the last person.

Threat and Error Management (TEM): threats are external events (weather, terrain, traffic), errors are crew actions; the countermeasures are avoidance, trapping and recovery.

Threats are classified as environmental, organisational or operational; errors as aircraft handling, procedural, communication or decision errors.

Undesired aircraft states (e.g. unstable approach, wrong runway, altitude deviation) are the link between errors and accidents; recognising and recovering from them is the core TEM skill.

Just culture: distinguishes human error (console), at-risk behaviour (coach) and reckless behaviour (sanction); it encourages reporting without removing accountability.

Safety reporting: confidential/non-punitive systems increase reporting; reporting rates are a leading indicator, while accident rates are a lagging indicator.

Risk assessment uses likelihood x severity; risk must be assessed before flight (threats) and continuously in flight (changes).

LOSA (Line Operations Safety Audit) observes normal operations to collect threat and error data; it is proactive, not an inspection or a test.

Safety is the state in which risk is acceptable; safety management is the organisational process of identifying hazards, assessing risk and mitigating it (SMS: safety policy, risk management, assurance, promotion).

The Swiss cheese model: defences have holes; an accident requires the holes to align; the goal is to add and strengthen defences rather than blame the last person.

TEM: threats are external events (weather, terrain, traffic), errors are crew actions; the countermeasures are avoidance, trapping and recovery.

Threats are classified as environmental, organisational or operational; errors as aircraft handling, procedural, communication or decision errors.

Undesired aircraft states (e.g. unstable approach, wrong runway, altitude deviation) are the link between errors and accidents; recognising and recovering from them is the core TEM skill.

Just culture: distinguishes human error (console), at-risk behaviour (coach) and reckless behaviour (sanction); it encourages reporting without removing accountability.

Safety reporting: confidential/non-punitive systems increase reporting; reporting rates are a leading indicator, while accident rates are a lagging indicator.

Risk assessment uses likelihood x severity; risk must be assessed before flight (threats) and continuously in flight (changes).

LOSA (Line Operations Safety Audit) observes normal operations to collect threat and error data; it is proactive, not an inspection or a test.

Safety is the state in which risk is acceptable; safety management is the organisational process of identifying hazards, assessing risk and mitigating it (SMS: safety policy, risk management, assurance, promotion).

The Swiss cheese model: defences have holes; an accident requires the holes to align; the goal is to add and strengthen defences rather than blame the last person.

TEM: threats are external events (weather, terrain, traffic), errors are crew actions; the countermeasures are avoidance, trapping and recovery.

Threats are classified as environmental, organisational or operational; errors as aircraft handling, procedural, communication or decision errors.

Undesired aircraft states (e.g. unstable approach, wrong runway, altitude deviation) are the link between errors and accidents; recognising and recovering from them is the core TEM skill.

Just culture: distinguishes human error (console), at-risk behaviour (coach) and reckless behaviour (sanction); it encourages reporting without removing accountability.

Safety reporting: confidential/non-punitive systems increase reporting; reporting rates are a leading indicator, while accident rates are a lagging indicator.

Risk assessment uses likelihood x severity; risk must be assessed before flight (threats) and continuously in flight (changes).

LOSA (Line Operations Safety Audit) observes normal operations to collect threat and error data; it is proactive, not an inspection or a test.