A Case Study of Formal Model based System Safety Analysis in Aviation

With the increasing complexity of safety-critical systems, it's a great challenge to improve the safety during the stage of system designs. Model based complex system design and formal analysis are an important system safety modelling and analysis methodology. In this paper, a case study is given to show how to apply this method into aerospace industry, that is, a Wheel Brake System (WBS) (which is a typical safeiy-critical sample system adopted in an aviation standard SAE-AIR6110) is used for demonstration of modelling and formal analysis. In AIR6110 standard, the requirement semantics described by natural language are ambiguous. Therefore, it is necessary to eliminate the ambiguity and establish a formal model of WBS system firstly, including: the structure of WBS is analyzed hierarchically at the system model design level, and the functions of WBS system described by natural language are strictly modeled in a formal language (SLIM, a subset of AADL). The possible faults of the system elements are considered and various types of fault modes are designed. Also the semantics of faulty behavior of the formal functional model is extended based on these fault modes. Then the safety of the extended system model is analyzed, such as FTA analysis. The case analysis demonstrates the validity and practicability of the model-based safety analysis method in Industrial systems.