Contributions and limitations of “drift into failure” and “safety boundaries” identification and management in accident investigations

Authors : Aslanides, M, Jollans, J-Y. y Amalberti, R.

2d Resilience Engineering Symposium, Juan les Pins, 2006

This paper explains how aviation accident investigators understand system’s drifts, their main contributing factors and the way safe boundaries can be restored through concrete actions. We believe their experience can improve our knowledge about drifts into failure mechanisms and about action models to manage these drifts. After analyzing 70 french airforce accident reports and having noticed the total absence of violation’s written trace, we interviewed 8 accident investigators and confronted them to the analysis of an accident report in order to assess if they have managed the risks related to violations. Our results show they know the difference between “work as imagined” and “work as actually done”, they detect the reasons of drifts, establish the boundaries not to be crossed, and give guidelines based on their judgment of the drift validity. When assessing operator’s interpretation of rule acceptability and flexibility, and violation’s validity, accident investigators judgments are naive or too tolerant, depending on the “distance” between the analyst and the analyzed situation. What blocks violation management is the fragile analysis of operator’s intention and of the socially accepted rules to which behaviour should be compared. Proactive work analysis in safety-emergent “normal” conditions and professional reflective activities about drifts into failure and safety boundaries should improve safety.

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