The paper describes the design and structural optimisation of a mechanical system from the functional, safety, reliability and cost viewpoints, using a flexible, rapid approach which was developed from the integration of two methodologies: Axiomatic Design and FMEA. In particular, thanks to the information obtained from Axiomatic Design, FMEA is not carried out on the entire system but only on the components and subsystems which are more critical. This makes it possible to establish an order of priority for intervening on components or Design Parameters of a system which can be applied both prior to designing the system or in the diagnostic and validation phase of an already existing product. This approach has been validated by its application to the electro-hydraulic command of the working device of an Orenstein & Koppel (O&K) earth-moving machine.