What is a Fault Tree Analysis (FTA) and what are basic events?

• A. FTA is a top-down deductive method to identify causes of a system failure; basic events are the lowest-level failure causes.
• B. FTA is a bottom-up inductive method; basic events are the middle-level causes.
• C. FTA analyzes only hardware faults; basic events are software faults.
• D. FTA is a qualitative-only method; basic events have no meaning.

Answer: (A)

Fault Tree Analysis uses a top-down deductive approach to show how a system failure can occur. You start with the undesired top event (the failure you want to prevent) and break it down through logic gates (such as AND and OR) into contributing causes, iterating until you reach events that cannot be decomposed any further. These are the basic events. They are the lowest-level, primitive causes that directly lead to the top event and serve as the leaves of the fault tree. Basic events can be failures of components, human errors, or external events, and they are the primary quantities you would use if you quantify the tree to estimate the probability of the top failure.