Reliability availability maintainability safety (RAMS) management of railway signalling systems & FMEA-FTA analysis application

Today, high speed railway transportation systems are essential for countries because existing road and air transportation systems have become unable to carry the burden of excessive traffic. Special attention has been given to change this situation in many countries of Europe and Asia with high speed railway systems. Behind the main reason for constructing high speed railway systems in the world is to use potentiality of ability of carrying more passengers and loads in a short time safely and cheaply. With the development of railway technology, safety and comfort concept has gained more importance. This is caused by the railway system engineers to focus on the concept, RAMS. In railway systems, there are many studies so far in safety and risk analysis. However, in our country and in our rapidly growing rail infrastructure technical infrastructure that our country has not developed sufficiently to be of any system engineering legislation. Railway organizations have been a more wide-spread research area than any other transportation methods, in the manner of its characteristics and competition advantages. As a result, railway organizations have been interested in reengineering processes in order to develop innovative solutions on availability, reliability, efficiency in cost, and advanced technologies. For example, gradual liberalization in transportation and less auditing have yielded separation of management and infrastructure, competition among modes, and collaborative serviceability. Reliability, availability, and efficiency in cost have been most important matter of railway industry. So, reliability, availability, and efficiency in cost for a railway system require to be developed continuously. Railway companies developed some specific engineering applications in their railway design and developed projects. For example, by many railway companies, RAMS management with system engineering has been used to build availability, reliability, and cost efficiency concepts in early project development phase. RAMS management is an engineering area aiming to combine reliability, availability, sustainability, and safety with system engineering processes and to ensure to implement designated railway timetable. In recent years, implementing a designated railway timetable well-timed, reliably, and cost efficiently has become a fast growing area in engineering. Also, this area has an important potential in creating advantages in competition of railways against other means of transportation. So, RAMS management is a very crucial subject in today's global railway industry and its importance in local railway industries shows an increasing trend. Railway RAMS standards were created based on BS IEC 61508 standards. BS IEC 61508 series are representative standards for safety management of electric/electronic related system. 3 railway RAMS management standard have been developed by CENELEC and they are based on BS IEC 61508 standards. BS EN 50126-1 was first published in 1999 as railway RAMS management basic principles and applications. BS EN 50128 is a RAMS management standard for the software used in operating, signalling, and communication of railway included systems and was developed in 2008. BS EN 50129 is a RAMS management standard on railway signalization system hardwares and was published in 2003. Risk identification is the main part of system engineering and RAMS management. Risk is defined as results of a failure. Risk identification is the base of RAMS management application. Below are two definitions for concept of risk: Risk is a combination of severity of results and expected frequency of occurrence. Risk is negative effect occured according to its level. In general, following 4 items are required to define the risk quantitatively and qualitatively. • Main causes of potential failure • Failure mode • Damage or effect • Occurrence possibility Risk assessment is definition, identification and assessment process of a risk in quantitative and/or qualitative manner. Risk assessment generally seeks for the answers of following questions: • What can happen and why? (By defining the risk) • What are the causes of failure? (By defining the severity of results) • What is the probability of a failure? (By specifying the frequency of failure) • What is the risk level? Can the risk be tolerated or accepted? Or, is a specific control required? (By applying risk assessment techniques) Risk assessment enables decision making in RAMS (risk assessment management systems) by enabling to deeply understand the risk, its causes, results, and occurrence probabilities. Risk assessment also enables applying RAMS management successfully in following 5 topics: • Choosing from alternative risks and alternative options, • Specifying risk priorities to identify decision making and risk management options, • Choosing proper risk management strategies, • Identifying risk activity to take the risk under control, and • Specifying the risk level to be controlled. This study was prepared for a local signalling system at Istanbul Ulasim Inc. examples of risks encountered during the course of the signaling .For further studies, it was made into a report. This study focuses on RAMS and systems engineering concepts, risk analysis, a summary of the literature after the information about these concepts and the methods used to calculate quantitatively significant risks are discussed. These methods include FMEA and FTA was preferred for use in the analysis methods and analysis as complementary to each other were investigated in detail. Consequently, the working examples presented in the above-mentioned railway operation. The focusing case study is on FMEA and FTA analysis of the Mescid-i Selam Station Signaling System which is operated in fixed-block signaling system manner. Another aim of this study is to realize the application of the defined FMEA and FTA based risk assessment method and to establish the failure events & causes related to fixed-block signaling systems. This study, includes a rail project starting with the planning, designing, commissioning, operation and, maintenance until the termination of the system. This study should be a basic source which includes risk analysis methods of the system. Studies to be carried out later, to try to find answers to the questions, such as; in what way a system passed through these stages by international certification bodies and, how it should obtain a system according to international commissions authority.