Abstract: Safety critical mass produced products are today being implemented without mechanical backup. Most of these will have distributed real-time computer networks, which must be ultra-dependable. Here a development method for future control-by-wire systems is presented. By using a scalable software architecture and the systems' intrinsic redundancy it is possible to achieve the dependability requirements cost-effectively. The method starts with analyzing a functional task-graph, which gives input for developing a non-redundant architecture. This non-redundant architecture is modified to meet the dependability requirements by adding hardware redundancy. The functionality implemented in software is allocated to the network according to some optimization criteria. The proposed method has been used in two cases; a fly-by-wire aircraft and a drive-by-wire car.