Fast-time Simulation for Event Sequence Diagrams in Aviation Safety

The Integrated Safety Assessment Model (ISAM) is being developed by the FAA to provide a baseline risk assessment for the National Airspace System. The model consists of a set of event trees, each describing a set of possible event sequences occurring following an initiating event, such as an engine failure. Probabilities associated with the initiating events and end events of the trees are typically quantified via historical incident and accident data. However, the intermediate branching probabilities are not quantified directly, but rather indirectly assumed. This case study provides a physics-based simulation of an aircraft taking off to help quantify the branching probabilities in the trees. The simulation consists of a continuous-time aircraft dynamic model and a discrete-event simulation of the event tree. Results show that accident probabilities are sensitive to a number of parameters that are not directly captured in the original event trees.