Aircraft fuel consumption, noise, and air pollutant emissions have become very important issues in the last decade, due to their environmental and cost impact. In order to reduce them, one of the current ways is to develop innovative on-board system architectures, which use electrical power as main source. The development of these new systems can be addressed through a Multidisciplinary Design Optimization (MDO) approach, which involves different disciplines simultaneously, to optimize the considered system. One relevant discipline - in this MDO problem - is Reliability, Availability, Maintainability and Safety (RAMS), which allows the assessment of the dependability of aircraft systems. In the last years, different RAMS models and methods have been defined, considering both conventional and innovative architectures.