Improvements in industrial productivity require the creationof a reliable design in the shortest possible time. This isespecially significant for designs that involve computerintensive analyses. The Robust Concept Exploration Method(RCEM) embodies a systematic approach to configuringcomplex engineering systems in the early stages of productdesign by introducing quality considerations based on the robustdesign principle. Approximation techniques are employed inthe RCEM to replace intensive analysis programs for saving thecomputational time and cost, thereby increasing the efficiencyof a design process. In this paper, the applicability of theRCEM for facilitating multiobjective complex systems designis examined by applying it to the propulsion system conceptualdesign process at Pratt & Whitney. Various approximationtechniques are studied and a new strategy is proposed to enhancethe existing model approximation techniques embodied in theRCEM.