Integration of Formal Methods into System Safety and Reliability Analysis

System verification and hazard analysis procedures on critical systems are traditionally carried out in separate stages of product development and by different teams of engineers. Safety and hazard analyses have for several decades been based on techniques such as fault tree analysis (FTA), whereas system verification is carried out by testing and simulation. Recent years have seen an increasing interest in application of formal methods for detecting design errors at early development stages. In this paper we propose a technique whereby both safety correctness proofs and reliability analysis, like FTA, can be performed on one design model: a model of the system in propositional logic and integer arithmetic. An obvious benefit is that the two parallel activities take place in the development process in a natural manner, and using a common model. The model is used for performing FTA-like analysis without building the fault-tree. We describe the application with examples from the aerospace domain and show how the theorem prover NP-Tools can be used to combine the two types of analysis.