Integrating safety and formal analyses using UML and PFS

Where software systems are safety critical, for example in aircraft engine control, it is necessary to carry out safety analysis on designs in support of certification. We argue that there is also significant value in formally validating such a design. Few “classical” formal notations and methods are geared towards embedded systems. We illustrate one such method known as Practical Formal Specification (PFS), showing how it can be integrated in a UML context with various forms of safety analysis. The PFS method was developed to extend classical approaches in the development of embedded software systems in a way that adds engineering value, and fits into existing well-established frameworks. We exemplify the approach to model the reverse thrust selection function of the thrust reversal system of a turbo-jet engine.