The Psychology of Quality and More

Fault Tree Analysis (FTA)

The failure of an item in a system is often caused by the failure of other items. Fault Tree Analysis, or FTA, provides a method of breaking down these chains of failures, with a key addition for identifying combinations of faults that cause other faults. 

Combinations of faults come in two main types: (a) where several items must fail together to cause another item to fail (an 'and' combination), and (b) where only one of a number of possible faults need happen to cause another item to fail (an 'or' combination).

The FTA diagram shows faults as a hierarchy, with two other symbols to show the 'and' and 'or' combinations, as in the illustration. These are called gates, as they prevent the failure event above them occurring unless their specific conditions are met.

See also:

Toolbook chapter: Fault Tree Analysis (FTA)