A prototype preliminary design task for gas turbines is set up to outline the four major requirements a preliminary design program must typically meet: assessment of all major engine components and their interrelations; inclusion of all relevant disciplines; designing over several operating points; and model fidelity zooming at least for individual components. It is described how the MOdular Performance and Engine Design System (MOPEDS)-MTU Aero Engines' software package for the preliminary design of airborne and stationary gas turbines-fulfills these requirements. The program structure, the graphical user interface, and the physical models are briefly presented. A typical design example is carried out emphasizing the necessity for a numerical procedure to find a solution to the many variables and constraints that the design problem comprises. Finally, some dominating multidisciplinary effects are discussed.