These design features include potential hardware failures and common mode failures. Models are constructed for each system covered in the risk assessment. Success criteria are identified in conjunction with the event tree development. System models are generally fault trees developed to a level of detail consistent with available information. Common cause contributors and potential systems interactions are included to ensure proper integration into the analysis.
Fault trees are a widely accepted means for evaluating the failure potential of systems.
The integration of event trees and fault trees provides an analytical approach capable of handling the complexities associated with modeling potential casualty sequences in a manner that leads to quantification. The figure below is a simplified event tree suitable for aircraft risk analysis. Knowing the probability of critical system failure at each node will allow calculation of the probability of individual or groups of event sequences. This probability can be converted to other units such as per year, per passenger mile, per flight hour, or others through proper use of other statistical or frequency data. The event sequence analysis can be customized to the specific risk analysis scope and objective.