Fault Tree Analysis

Fault Tree Analysis

Fault tree analysis (FTA) is a top down, deductive failure analysis in which an undesired state of a system is analyzed using boolean logic to combine a series of lower-level events. This analysis method is mainly used in the field of safety engineering and Reliability engineering to determine the probability of a safety accident or a particular system level (functional) failure.

In Aerospace the more general term "system Failure Condition" is used for the "undesired state" / Top event of the fault tree. These conditions are classified by the severity of their effects. The most severe conditions require the most extensive fault tree analysis. These "system Failure Conditions" and their classification are often previously determined in the functional Hazard analysis.

FTA can be used to:

• understand the logic leading to the top event / undesired state.
• show compliance with the (input) system safety / reliability requirements.
• prioritize the contributors leading to the top event - Creating the Critical Equipment/Parts/Events lists for different importance measures.
• monitor and control the safety performance of the complex system (e.g. Is it still safe to fly an Aircraft if fuel valve x is not "working"? For how long is it allowed to fly with this valve stuck closed?).
• minimize and optimize resources.
• assist in designing a system. The FTA can be used as a design tool that helps to create (output / lower level) requirements.
• function as a diagnostic tool to identify and correct causes of the top event. It can help with the creation of diagnostic manuals / processes.