# Fault Tree Analysis

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1 FAULT TREE ANALYSIS 1. Introduction FTA is a deductive, failure-based approach. As a deductive approach, FTA starts with an undesired event, such as failure of a main engine, and then determines (deduces) its causes using a systematic, backward-stepping process. In determining the causes, a fault tree (FT) is constructed as a logical illustration of the events and their relationships that are necessary and sufficient to result in the undesired event, or top event. The symbols used in a FT indicate the type of events and type of relationships that are involved. The FT is a qualitative model that provides extremely useful information on the causes of the undesired event. The FT can also be quantified to provide useful information on the…show more content…
A fault tree is composed of a complex of entities known as “gates” that serve to permit or inhibit the passage of fault logic up the tree. The gates show the relationships of events needed for the occurrence of a “higher” event. The “higher” event is the output of the gate; Chapter “Lower” events are the “inputs” to the gate. The gate symbol denotes the type of relationship of the input events required for the output event. Figure 1- 1 shows a simple fault tree. FTA Logic Symbols GRAPH BASED METHODS 3 FAULT TREE ANALYSIS • • • • • • • • • • • • OR Gate (a): used when output event occurs when one or more input events occur. AND Gate (b): used when output event occurs when all input events occur. Priority AND Gate (c): like AND gate but input events occur in a specified order. Exclusive OR Gate (d): used when output occurs when one and only one of the input events occur. Delay Gate (e): used when output event occurs after a specified time delay. Inhibit Gate (f): used when output event occurs based on a conditional event occurring. M-out-of-N Gate (g): used when output event occurs based on a m out of n input events occurring. Resultant Event (h): used to represent an event resulting from some combination of preceding fault events. Basic Fault Event (i): used to represent failure of component or subsystem. Incomplete Event (j): used to represent a fault event whose cause has not yet been determined. Conditional Event (k): used to represent the