To: Belgique
Several years ago various human factors organizations in concert with reliability organizations tried to quantify human error. In essence to account for human error in systems and component failures. They worked for several years but never came up with a workable system. I don’t know if the following related to their findings but many organizations (Reliability) eliminated manufacturing error and maintenance error in the preparation of FMECAs because it could not be quantified like a failure rate even if the failure rate used was meaningless. I recently performed an FMECA on a business jet and included maintenance error, manufacturing defect, design defect as the mode of failure and I was told to remove them and only use the inherent failure rate for the part. In doing this it is assumed that the part will only fail at the specified rate and only at that rate and all of the other things that enter into the equation do not count.
The closest they came was in an Air Force study that correlated actual failures with false removals in order to calculate MTBUR (Mean Time Between Unscheduled Removal).
In the preparation of the FTA maintenance error can be a collateral driver and plugged into the diagram but it does not have a quantity (rate of human error) and could be listed only as a contributing factor in the failure.
