This article illustrates the use of optimization methods in the development of a new regional aircraft. These aircraft are more sensitive to changes in operational requirements than other types due, in part, to their high zero-fuel weight ratio. For such aircraft it is essential that the best information possible be available to the designers in the early project definition phases. The identification of optimum aircraft configurations and mission characteristics for various operational and configurational options constitutes a vital part of this knowledge. A series of industrially- related design studies are presented. These include 1) the selection of the baseline config- uration; 2) parameter sensitivity investigations; 3) analysis of aircraft and engine stretch potential; and 4) generalized (rubber engine) designs. This article concludes with a discussion on the merits of optimization studies in aircraft project design and offers some suggestions for changes to the strategies adopted. I NITIAL aircraft project design always presents difficult decision areas to designers. Once a particular aircraft con- figuration has been finalized it is too expensive to introduce major changes. Considerable pressure is exerted on the proj- ect team to "get it right." The situation is further complicated by the changing technical and commercial environment sur- rounding the design. Some of the possibilities for change in- clude the choice of engine supplier, improvements in engine performance, introduction of new airframe and aircraft sys- tems, technology improvements, the emergence of new com- petitor aircraft, and changing operational and regulatory frameworks. The designers are therefore concerned with the specification of the initial design and the strategy for future aircraft development. The chosen aircraft configuration is un- likely to be exactly matched to the initial operational speci- fication but it must not be compromised to an extent that the first design i§ uncompetitive. It is within this context that the value of the optimum design method should be judged. The industrial design team places strong emphasis on com- ponent design aspects. These are pursued in fine detail and constitute substantial technical effort. Past experience has shown that careful control of the aircraft detail design in the early stages offers the best method of avoiding technical difficulties later in the design cycle. Broader-based optimization studies can be considered as complementary to this detail design ef- fort. Together they provide both micro- and macro-design scenarios which help the designers in their difficult choice of initial aircraft specification and in subsequent developments. In the early stages of the design when the aircraft geometry and performance criterias have not been fixed, the optimi- zation studies are used to identify the absolute "best" con- figuration with respect to various operational specifications. This enables the designers to judge the sensitivity of the design with respect to variations of the aircraft geometrical and per- formance parameters. Once the baseline design has been es- tablished the optimization studies are used to evaluate the tolerance available in the selection of aircraft operational pa- rameters. Configurational features (e.g., rear-engine posi- tion) can also be assessed to show the quantifiable penalties/