A Model-Based RAMS Estimation Methodology for Innovative Aircraft on-board Systems developed in a MDO Environment

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. However, most of them rely on a document-based approach, which makes difficult and time consuming the use of information gained through their analysis to improve systems architectures. On the contrary, a model-based approach would make easier and more accessible the study of systems reliability, as explained in several current studies. The aim of the thesis is to use a model-based approach to define new RAMS estimation models. Through these models, it is possible to define the dependability of innovative on-board system architectures developed in MDO environment. Different analyses (such as FMEA, FHA, RBD and FTA) are carried out following a model-based approach in order to identify potential failure modes of a Flight Control System (FCS) architecure. Then, some architecture changes are applied to improve its reliability and safety. These changes involve a variation of the aircraft parameters considered in the MDO environment, which in turn allows knowing if an overall design improvement has been achieved.