Common Cause Failure Analysis for Aviation Safety Assessment Models

The Integrated Safety Assessment Model (ISAM) developed by the FAA models aviation accidents and incidents via event sequence diagrams (ESDs) and supporting fault trees. The model assumes that the basic events are independent. In reality, since many of the events include common elements, such events may be dependent. To address the impact of dependency among events, we apply a common cause failure (CCF) methodology to ISAM. First, a barrier-based approach is used to identify common elements that are shared between safety barriers in the model. From this, the beta (β)-factor model, a commonly used CCF method, is applied to calculate the end-event probabilities under the assumption of dependence among the events. The potential impact of including CCF factors is evaluated by varying the dependence parameter β. For some ESDs, the trend shows that increasing the dependency among CCF factors can significantly increase the end-event occurrence probability. Thus, common cause elements may be important to consider in these models.