Sensitivity analysis of event sequence diagrams for aircraft accident scenarios

The Integrated Safety Assessment Model (ISAM) is being developed to provide a baseline risk assessment for the National Airspace System and to evaluate safety implications of proposed changes. The causal risk model in ISAM is a hybrid model of event sequence diagrams (ESDs) and fault trees and represents accident and incident scenarios. ISAM contains several thousand parameters. This paper evaluates the significance of these parameters within the model with respect to several importance metrics in order to identify the most important parameters. The analyses are conducted for pivoting events and underlying fault tree events of individual ESD as well as across all ESDs based on both the accident frequency and the fatality frequency.