13.1 Fundamental Human Factors Concepts
Key Takeaways
- Nig. CARs 8.14.11.4 provides that the operator's cabin crew training programme should include human factors training.
- The SHELL model analyses the interfaces between the human at the centre and software, hardware, environment and other people, and most incidents arise at an interface rather than within a single element.
- Errors are classified as slips and lapses in execution, mistakes in planning, and violations, which are deliberate departures from procedure; each requires a different countermeasure.
- Situational awareness has three levels — perceiving the elements, comprehending their meaning and projecting future state — and loss of awareness usually begins at the perception stage.
- Fatigue degrades vigilance, reaction time, memory and mood, and its effect is worst during the window of circadian low in the early hours of the morning.
Why human factors is a regulated subject
Nig. CARs 8.14.11.4 requires the operator to establish and maintain a cabin crew training programme designed to ensure competency for assigned duties, and states that the programme should include Human Factors training. Recurrent training under 8.10.1.34 additionally requires joint CRM with flight crew and flight operations officers every 12 calendar months. Human factors is therefore not a soft supplement to technical training; it is part of the regulatory training set.
The reason is empirical. Aircraft systems fail rarely. Human performance varies constantly, and the majority of accidents and serious incidents involve human performance as a contributing factor. Human factors is the discipline that studies why competent, trained, well-intentioned people make errors, and what can be designed around them.
The SHELL model
SHELL places the liveware — the human being — at the centre and examines the interfaces with everything around them. The insight is that failure occurs at the joins, not usually inside a single block.
| Interface | Meaning | Cabin examples |
|---|---|---|
| Liveware – Software | The person and the procedures, manuals, checklists, training and symbology | An ambiguous cabin secure checklist; a manual revision that never reached the crew; a door drill that differs between two variants of the same type |
| Liveware – Hardware | The person and the equipment | An arming lever whose two positions look similar; a PBE that is difficult to don quickly; an extinguisher stowage that is awkward to reach |
| Liveware – Environment | The person and the physical and operational surroundings | Noise that masks a call; dim lighting during a night check; heat on the ground in Lagos; time pressure from a late departure; low humidity and dehydration |
| Liveware – Liveware | The person and other people | A briefing that was rushed; a junior crew member who does not challenge a senior one; a flight deck that does not welcome cabin reports |
When something goes wrong, the useful question is which interface failed, not who was careless.
Error and violation
| Type | Definition | Example | Countermeasure |
|---|---|---|---|
| Slip | The plan was right; the action was not carried out as intended | Reaching for the correct control and operating the adjacent one | Design, cross-check, standard sequences |
| Lapse | A memory failure; a step is omitted | Forgetting to disarm one door after an interruption | Checklists, cross-checks, restart-on-interruption discipline |
| Mistake | The action was carried out as intended, but the plan was wrong | Opening a door on the side where fire is present because the viewport was not checked | Training, procedures, decision rules |
| Violation | A deliberate departure from a known procedure | Skipping the cross-check because the turnaround is tight | Culture, supervision, removing the pressure that makes the shortcut attractive |
The distinction matters because the remedies differ. A lapse is corrected by a system that catches omissions; a violation is corrected by addressing why the shortcut seemed reasonable at the time.
Routine violations — small shortcuts that have never yet caused harm — are the most dangerous category in cabin operations, because they erode the barriers that were designed to catch the slips and lapses. The cross-check exists because arming errors are foreseeable; skipping it because "I always get it right" removes the barrier precisely for the occasion on which the error occurs.
Situational awareness
Situational awareness has three levels:
- Perception — noticing the elements in the environment: the smell, the indication, the passenger's behaviour.
- Comprehension — understanding what they mean together: this smell plus this indication plus this location equals a probable electrical fault.
- Projection — anticipating what will happen next: if this is electrical and undetected, we will have smoke in the cabin within minutes.
Most losses of awareness begin at perception: the cue was there and nobody noticed it. Common causes are fixation on one task, distraction, overload, complacency during routine operations, and fatigue.
Practical countermeasures: deliberate cabin walks rather than passing glances; verbalising what you have noticed to another crew member, which converts a private observation into shared awareness; re-checking after any interruption; and treating "something feels wrong" as data rather than as a mood.
Stress
Stress is the body's response to demand. A moderate level improves performance; beyond the peak, performance falls away sharply.
- Acute stress — an emergency, a medical event, an aggressive passenger. Effects include tunnel vision, auditory exclusion, degraded fine motor control and a marked loss of ability to improvise. This is exactly why emergency drills are trained to automaticity: under acute stress a crew member performs what is deeply practised, not what is cleverly reasoned.
- Chronic stress — accumulated from rostering, personal circumstances, financial pressure or workplace conflict. It degrades sleep, mood, judgement and health, and it is cumulative.
- Countermeasures — controlled breathing, a fixed first action to break the freeze, well-learned procedures, talking to another crew member, and using the operator's support arrangements.
Fatigue and the circadian rhythm
Fatigue is a physiological state that reduces alertness and impairs performance. Its effects — slowed reaction, lapses of attention, reduced memory, poorer decision-making and irritability — closely resemble the effects of impairment.
- The circadian rhythm drives a natural low in alertness in the early hours of the morning, the window of circadian low, and a smaller dip in the early afternoon.
- Sleep debt accumulates; a series of short nights degrades performance even when each night felt survivable.
- Time zone transitions desynchronise the body clock from local time, and recovery takes roughly a day per time zone crossed.
- The regulatory countermeasures are the duty and rest limits in Nig. CARs 8.12 covered in the air law chapter; the personal countermeasures are sleep hygiene, strategic use of rest opportunities, hydration and nutrition, and the professional honesty to report unfitness for duty.
The regulation supports that honesty: Part 8 requires that a flight is not commenced if a crew member is incapacitated by any cause including fatigue. Declaring fatigue is a compliance action, not an admission of weakness.
A crew member is interrupted during the disarm sequence and later cannot recall whether she completed it. Which error type is this, and what is the designed countermeasure?
Which level of situational awareness is most commonly lost first?
Why are routine violations regarded as particularly dangerous in cabin operations?
Which statement about fatigue and Nigerian regulation is correct?