System design methodology becomes a strategic activity in the industrial competition. Obtaining substantial reduction of time to market for complex and reliable products is one of the priorities for the manufacturers. Top down design, automated generation of architecture, co-design, virtual prototyping, etc. are already identified as research topics which have to be privileged. To be efficient, each theoretical contribution must be inserted in a global procedure of project management where complementary elements such as marketing, technico-economic survey, road-mapping, internal know-how,.. must be considered. In this context, this paper will present a design methodology starting from the requirement statement until the technical realization of the product, and applied to the design of a Time Stress Measurement Device for the observation of aeronautical mechanical systems.