On System Safety and Reliability Methods in Early Design Phases : Cost Fo cused Optimization Applied on Aircraft Systems

Abstract: System Safety and Reliability are fundamental to system design and involve a quantitative assessment prior to system development. An accurate prediction of reliability and system safety in a new product before it is manufactured and marketed is necessary as it allows us to forecast accurately the support costs, warranty costs, spare parts requirements, etc. On the other hand, it can be argued that an accurate prediction implies knowledge about failures that is rarely there in early design phases. Furthermore, while predictions of system performance can be made with credible precision, within reasonable tolerances, reliability and system safety are seldom predicted with high accuracy and confidence.How well a product meets its performance requirements depends on various characteristics such as quality, reliability, availability, safety, and efficiency. But to produce a reliable product we may have to incur increased cost of design and manufacturing. Balancing such requirements, that are often contradictory, is also a necessary step in product development. This step can be performed using different optimization techniques.This thesis is an attempt to develop a methodology for analysis and optimization of system safety and reliability in early design phases. A theoretical framework and context are presented in the first part of the thesis, including system safety and reliability methods and optimization techniques. Each of these topics is presented in its own chapter. The second and third parts are dedicated to contributions and papers. Three papers are included in the third part; the first evaluates the applicability of reliability methods in early design phases, the second is a proposed guideline for how to choose the right reliability method, and the third suggests a method to balance the safety requirements, reliability goals, and costs.