The primary products of systems engineers all seem to be documents such, as specifications and trade-off studies. Communicating the requirements to hardware and software designers with documents is fraught with problems. By using a model-based approach to systems engineering, there is no ambiguity. The model fully defines the functional behavior, inputs and outputs, and the physical architecture, as well as the performance and resource requirements. This method provides a unified, consistent and traceable design. This paper describes the design of the Automotive Personal Assistance System (APAS) exploiting the features of the Global Positioning System, which is similar to the Cadillac OnStar System. It includes the entire systems engineering life cycle, from source requirements analysis, through behavior analysis and physical architecture, to verification and validation. The behavior model can be fully executed to verify its correctness long before money is wasted building prototypes. The use of the model-based approach will aid in the reduction of product cost and the increase in product quality