Human Error
Error models and theories, types of error in maintenance tasks, the Dirty Dozen, implications of errors, avoiding and managing error.
Human error, summary notes
- James Reason's model distinguishes error types: a slip (right intention, wrong action, e.g. torquing the wrong bolt), a lapse (forgetting a step), and a mistake (wrong plan followed correctly, e.g. misdiagnosing a fault).
- The Swiss Cheese Model shows that accidents rarely have one cause, they happen when holes (weaknesses) in successive defensive layers (design, procedures, training, supervision, inspection) momentarily line up.
- The "Dirty Dozen" (Gordon Dupont / Transport Canada) are twelve recurring precursors to maintenance 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.
- Errors are best managed with error-tolerant design (defences that catch an error before it causes harm, independent inspection, duplicate inspection for critical tasks) rather than by demanding zero mistakes from people.
- Implications of an uncaught maintenance error range from a minor rework to a hull-loss accident, which is why critical tasks (flight controls, engine controls) require independent duplicate inspection by a second, qualified person.
- ⚠ Exam trap: a violation is a DELIBERATE deviation from a known rule, unlike a slip or lapse (unintended); and error management works by avoiding, trapping and mitigating, not by demanding zero mistakes.
A technician intends to torque bolt A but, distracted, torques the visually identical bolt B instead. Which error type is this, per Reason's model?
A slip, the intention (torque the correct bolt) was correct, but the action was misapplied due to distraction, not a knowledge or planning failure.
The Dirty Dozen
The Dirty Dozen
Human error quiz
Human Error, quiz
1. In James Reason's model, forgetting a step in an otherwise correct plan is called a:
LapseSlipMistake2. Torquing the wrong, visually identical bolt due to distraction, while intending to torque the correct one, is an example of a:
SlipLapseMistake3. Misdiagnosing a fault and correctly carrying out the (wrong) resulting repair plan is an example of a:
MistakeSlipLapse4. The "Swiss Cheese Model" illustrates that accidents typically occur when:
Weaknesses in several successive defensive layers line upA single careless individual ignores all proceduresEquipment fails without any human involvement5. "Complacency" and "distraction" are both examples of items from the:
Dirty DozenSwiss Cheese Model layersSHELL model components6. A deliberate deviation from a known rule (not an accidental error) is a:
ViolationSlipLapse7. The three-part strategy for managing error is to avoid, trap and:
Mitigate the consequencesPunish the personIgnore the outcome8. A latent failure differs from an active failure in that it:
Lies dormant in the system until conditions expose itAlways causes immediate harmIs committed at the sharp end only