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Fault tree analysis helps determine the root cause of failure of a system using Boolean logic to combine a series of lower level events. FTA is a deductive analysis depicting a visual path of failure. It is a top‐down analysis that helps determine the probability of occurrence for an undesirable event. The analysis creates a visual record showing the logical relationships between events and failures that lead to the undesirable event. It easily presents the results of your analysis and pinpoints weaknesses in the system.

The fault tree analysis (FTA) was first introduced by Bell Laboratories and is one of the most widely used methods in system reliability, maintainability and safety analysis. It is a deductive procedure used to determine the various combinations of hardware and software failures and human errors that could cause undesired events (referred to as top events) at the system level.

To do a comprehensive FTA, follow these steps:

1 Define the fault condition, and write down the top‐level failure.

2 Using technical information and professional judgments, determine the possible reasons for the failure to occur. Remember, these are level two elements because they fall just below the top‐level failure in the tree.

3 Continue to break down each element with additional gates to lower levels. Consider the relationships between the elements to help you decide whether to use an “and” or an “or” logic gate.

4 Finalize and review the complete diagram. The chain can only be terminated in a basic fault: human, hardware, or software.

5 If possible, evaluate the probability of occurrence for each of the lowest level elements and calculate the statistical probabilities from the bottom up.