The design of safety critical systems calls for advanced software engineering models, methods and tools in order to meet the safety requirements that will avoid putting human life at stake. When the safety critical system encompasses a substantial interactive component, the same level of confidence is required towards the human-computer interface. Conventional empirical or semi-formal techniques, although very fruitful, do not provide sufficient insight on the reliability of the human-system cooperation, and offer no easy way to, for example, quantitatively compare two design options. The aim of this paper is to present a method with supporting tools and techniques for engineering the design and development of usable user interfaces for safety-critical applications. The specific application area that we consider is air traffic management but most of the results will be valid for any application areas with similar requirements.