Human Error and Reliability
What the domain covers
This domain examines error models and reliability: the error chain, the Swiss cheese model, error types (slips, lapses, mistakes, violations), and the difference between active failures and latent conditions. Candidates must understand Reason's model, the SHEL/SHELL link, and the concept of error management rather than error elimination.
Concepts to master
- Slips and lapses: skill-based, unintended actions; slips are observable actions, lapses are memory failures.
- Mistakes: rule-based or knowledge-based; the plan itself is wrong.
- Violations: routine, situational, exceptional and optimising.
- Swiss cheese: defences have holes; accidents occur when holes align. Latent conditions (poor design, weak procedures) lie dormant; active failures are the sharp end.
- Reliability: humans are reliable in routine tasks but degrade under stress, fatigue and high workload.
Question traps
Questions often ask whether an action was a slip or a mistake. If the intention was correct but execution failed, it is a slip or lapse. If the intention itself was wrong, it is a mistake. Also watch for the claim that 'all errors are avoidable' (false) or that 'violations are always reckless' (routine violations are often normalised practice).
Worked example / rule of thumb
A pilot selects the wrong frequency despite intending the correct one: a slip (skill-based). A pilot plans a route using an out-of-date rule: a rule-based mistake. Rule of thumb: ask 'was the plan right?' If yes, execution error; if no, mistake.