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Functional Resonance Analysis Method (FRAM), which defines a systemic framework to model complex systems from the perspective of function and views accidents as emergent phenomenon of function's variability, is playing an increasingly significant role in the development of systemic accident theory. However, as FRAM is typically taken as a theoretic method, there is a lack of specific approaches or supportive tools to bridge the theory and practice. To fill the gap and contribute to the development of FRAM, (1) function's variability was described further, with the rules of interaction among variability of different functions being determined and (2) the technology of model checking (MC) was used for the analysis of function's variability to automatically search the potential paths that could lead to hazards. By means of MC, system's behaviors (normal or abnormal) are simulated and the counter example(s) that violates the safety constraints and requirements can be provided, if there is any, to improve the system design. The extended FRAM approach was applied to a typical air accident analysis, with more details drawn than the conclusions in the accident report issued officially by Agenzia Nazionale per la Sicurezza del Volo (ANSV).

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Many incidents show that even if no failure occur, system can go wrong because of the interaction or logical design problem and lead to undesired result. These kinds of problem are derived from system design and it is necessary to analyze their existence during the functional design phase. Accident rehearsal means the development of the operational process of a specific system from initial states to final states. Its purpose is to determine whether an unexpected state or event is reachable from one specific initial state of the system. Based on this concept, model checking technique is used because of its ability to exhaustively and automatically check whether a system model meets a given specification. To find the problems of interaction and cooperation between functions, this paper proposes a functional model checking method for the requirement of complex system accident rehearsal after functional logic design. Time automata are used to system functional modeling and safety requirement is treated as property need to satisfy. With model checking tool UPPAAL, final results about whether these properties are satisfied are given and counterexamples can be gained to guide the finding of potential accident process and design improvement. At last, it illuminates how to apply this method to accident rehearsal with an actual escalator accident.