The comparison of possible turbofan engine architectures is a vital task during the preliminary design phase of such new products. Already at this point of the product life cycle the architectural decisions which are based on a minimum of product information define a major part of the product life cycle cost. For turbofan engines unit cost is a major part of the life cycle cost. It is not sensible to thrive for a detailed cost assessment in such an early design phase, since neither the required information nor the required time would be available for such an exercise. Hence a cost comparison method is required which produces results of adequate accuracy and detail based on a less complex estimation methodology. The cost comparison methodology proposed in this paper is based on the requirements and methods of a detailed cost assessment. The required information and a possible method for a detailed assessment have been analyzed. In a second step a simplification of the detailed assessment has been derived. This simplified approach uses a minimized set of product data and relies on the similarity of product parts and sub-structures. It turns out that intense thoughts regarding the suitable structuring of the end product turbofan engine have been necessary to derive the method. The uncertainties of such an assessment and its limitations have been verified against a subset of parts of a modern aero engine. It is of importance to notice that the method is also based on the assumption that key parameters of the supply chain and the manufacturing and assembly of the Original Equipment Manufacturer (OEM) are constant. On one hand this restricts the method to a cost comparison method between architectures. The cost comparison methodology not only applies to engines which are manufactured using existing materials and manufacturing methods, but the estimation of the required data for the use of new materials and manufacturing methods still requires detailed analysis since the product structure and the detailed design may change significantly.Copyright © 2007 by ASME