Due to a shift of the major aviation concerns to focus on enhancements of the successful programs instead of pushing their successors, the need for new methodologies for aircraft system architecture design emerges. Challenging the existing requirements and reconsidering the functions and their allocation could help to dissolve the system specific development paradigm and lead to beneficial architecture concepts. To help understand the mechanisms and boundary conditions of developing fault-tolerant systems, the first part of the paper gives an overview of the successive process of architecture design. The significant architectural design decisions and the concurrent safety assessment process are discussed.One crucial step in the design space exploration of future aircraft system architectures is the allocation of the consumers to the available power sources. Within the paper a methodology for the optimization of the power allocation for flight control systems is proposed. With this methodology the evaluation of a large amount of architecture permutations on the basis of a preliminary system safety assessment regarding multiple top failure events is possible in a short time period. Furthermore the impact of power allocation on the average operational availability of an aircraft is estimated. Therefore the architecture permutations are evaluated based on their reliability to comply with the master minimum equipment list after a given time.The proposed methodology has been implemented into the MATLAB based tool OPAL and validated on basis of the power allocation of the AIRBUS A320. Furthermore, within the paper a case study for the power allocation of a flight control system based on SAKURAI-flaps is presented to illustrate the application of the methodology and the tool OPAL.