38 Fault Tree Analysis Liudong Xing 1 and Suprasad V. Amari 2 1 Department of Electrical and Computer Engineering, University of Massachusetts-Dartmouth, USA 2 Relex Software Corporation, Greensburg, USA Abstract: In this chapter, a state-of-the-art review of fault tree analysis is presented. Different forms of a a fault trees, including static, dynamic, and non-coherent fault trees, their applications and analyses will be discussed. Some advanced topics such as importance analysis, dependent failures, disjoint events, and multistate systems will also be presented. 38.1 Introduction The fault tree analysis (FTA) technique was first developed in 1962 at Bell Telephone Laboratories to facilitate analysis of the launch control system of the intercontinental Minuteman missile [1]. It was later adopted, improved, and extensively applied by the Boeing Company. Today FTA has become one of the most widely used techniques for system reliability and safety studies. In particular, FTA has been used in analyzing safety systems in nuclear power plants, aerospace, and defense. FTA is an analytical technique, whereby an undesired event (usually system or subsystem failure) is defined, and then the system is analyzed in the context of its environment and operation to find all combinations of basic events that will lead to the occurrence of the predefined undesired event [2]. The basic events represent basic causes for the undesired event; they can be events associated with component hardware failures, human errors, environmental conditions, or any other pertinent events that can lead to the undesired event. A fault tree thus provides a graphical representation of logical relationships between the undesired event and the basic fault events. From a system design perspective, FTA provides a logical framework for understanding the ways in which a system can fail, which is often as important as understanding how a system can operate successfully. In this chapter, we first compare the FTA method with other existing analysis methods, in particular, reliability block diagrams, and then describe how to construct a fault tree model. Different forms of fault trees, including static, dynamic, and non-coherent fault trees and their applications will also be discussed. We then discuss different types of FTA as well as both classical and modern techniques used for FTA. We also discuss some advanced topics such as importance analysis, common-cause failures, generalized dependent failures, disjoint events, as well as application of fault trees in analyzing multistate systems and phased-mission systems. Some FTA software tools will be introduced at the end of this chapter.