An ITIL® fault tree analysis (FTA) is used when an undesired result of the ITIL® process was determined. It is a more complex cause-effect flow that people use to better understand, solve and prevent such potential failures from happening. In this technique, an undesired effect is taken as the root (or also called as top event) of a logic tree, then each situation or circumstances that could result to that effect is added to the tree as a series of logic expressions. The logical operator such as an AND or OR gates can be used to represent the series of errors and their corresponding causes.
To have a more detailed flow in coming up of an FTA, six simple steps on how to design it were cited by Hank Marquis. All you need is a pencil, a piece of paper and a working knowledge of the service. These are the following:
(a) Try to be more specific in coming up with a top-level event for your analysis. Some examples include potential or known error messages and possible scenarios that can be thought of based on the Service Level Agreement or SLA. (b) Write down all the faults under the top level event in boxes and connect the fault boxes to the top level event box by drawing lines. (a) For each fault, list as many causes as possible. (b) Draw a diagram and use the AND and OR logic operators. (c) Continue identifying the causes of the problem until the root cause is identified. (d) Consider coming up with countermeasures to find ways on how to resolve such issues and learn from them.