One of the key conditions to reach cost and time reductions is to ensure that expensive development phases (detailed design, industrialization), then series production phases, are performed with maximum efficiency. This leads also to make sure that the concept and feasibility phases, in which the large trade-offs are performed in a rather iterative manner, deliver sound baselines. As far as a design change is concerned during the development phase, the later it occurs, the more expensive it will be. Consequently, all disciplines must interact in an efficient manner, with a common objective, the successful and efficient development of the aircraft.