We describe how aircraft are designed in a large organization. We discuss the interactions among the different specialist departments during the design process, and the models used by each department. We observe that the main design choices are refinement operations on the design. The overall structure of the organized design process is one of coordinated refinement of models. We describe how the design negotiation process is controlled by an organizationally agreed sequence of commitment steps. We briefly discuss design elaboration, for wing design, within one commitment step.