Using Fault Modeling in Safety Cases

For many safety-critical systems a safety case is built as part of the certification or acceptance process. The safety case assembles evidence to justify that the design and implementation of a system avoid hazardous software behavior. Fault modeling and analysis can provide a rich source of evidence that the design meets safety goals. However, there is currently little guidance available to bridge the gap between the fault modeling that developers perform and the mandated safety case. In this experience report we describe results and open issues from an investigation of how evidence from software tool supported fault modeling and analysis of a spacecraft power system could assist in safety-case construction. The ways in which the software fault models can provide evidence for the safety case appears to be applicable to other critical systems.