We report on a formal requirements analysis experiment involving an avionics control system. We describe a method for specifying and verifying real-time systems with PVS. The experiment involves the formalization of the functional and safety requirements of the avionics system as well as its multilevel verification. First level verification demonstrates the consistency of the specifications whilst the second level shows that certain system safety properties are satisfied by the specification. We critically analyze methodological issues of large scale verification and propose some practical ways of structuring verification activities for optimising the benefits. Keywords---Formal specification, formal verification, safety critical systems, requirements analysis, avionics systems. I. Introduction T HIS paper reports on an experiment in the use of formal methods for producing and analyzing software requirements for a safety-related system. This work was conducted as part of the SafeFM ...

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