Dave W wrote:skydriller wrote:... the concept that in all safety critical systems you have to account for the fact that mistakes and errors occur...
As well as @skydriller's well-made wider point about successful safety systems, there's another relevant observation here - and that is the distinction between a "mistake" and an "error".
MISTAKE - Intended Action, Unintended Consequence.
- Mistake - Usually accidental. You know it’s wrong.
ERROR - Unintended Action, Unintended Consequence
- Error - Usually made due to the lack of knowledge. So, the action was wrong because it was different from the rules. The lack of knowledge may be due to ignorance, or it may be due to a misunderstanding. If the latter, it's very important to know why the misunderstanding occurred because lessons may need to be learned to avoid others misunderstanding it too.
When we talk about 'mistake' and 'error' we sometimes confuse the two. The definitions above are correct but there are some subtleties because errors can come in two different flavours. The generally used definitions are -
An error can be considered as:
“a planned sequence of mental or physical activity(ies) that fails to achieve its intended outcome”
They can come in two forms:
‘slip’ – incorrect execution of the plan ie where action is taken but it is not correct usually due to attentional or perceptual failures
‘lapse’ – failure to execute the plan, usually due to memory failure
Mistakes occur as a result of failure in the planning phase ie where a person intends to carry out an action, does so correctly but the action is inappropriate and the desired goal is not achieved
So when a pilot closes the mixture control lever instead of the throttle lever, that is a (error) slip. When they forget to select landing gear down, that is a (error) lapse. Where they wish to fly to airfield A but when planning enter airfield B into SkyDemon and then arrive at airfield B, that is a mistake.
So infringements may be the result of a mistake while planning or an error in flight due to a slip (such as descending too soon through the corner of CAS) or lapse (such as forgetting to change the altimeter from QFE to QNH on take-off). Incidents sometimes involve a mixture of mistake and error.
Best wishes
Mike