Fault Tree Analysis (FTA)
Definition
A top-down, deductive Boolean logic model that works backward from a specific undesired top event through AND/OR gates to identify minimal cut sets of basic failure combinations.
- Direction
- Top-down, deductive
- Logic
- Boolean AND/OR gates
- Starting point
- A specific undesired top event
- Output
- Minimal cut sets of basic failure combinations
Common questions
How does FTA differ from a bottom-up method like Failure Mode and Effects Analysis?+
FTA starts from a defined top event and works backward to find the combinations of basic failures that could cause it, while FMEA starts from individual component failure modes and works forward to their effects; FTA is better suited when the investigation already knows what went wrong and needs to find how, while FMEA is better for anticipating failures before they occur.
What is a minimal cut set and why does it matter in a fault tree?+
A minimal cut set is the smallest combination of basic events that, if they all occur together, is sufficient to cause the top event. Identifying these sets tells an investigator or engineer exactly which failure combinations are actually critical, rather than treating every branch of the tree as equally significant.
Related terms
- 5-Whys
- An iterative questioning technique that moves from a symptom to underlying causes by asking 'why?' repeatedly until a systemic explanation is reached.
- Barrier Analysis
- A method that identifies the physical, administrative, and procedural barriers that should have prevented harm, and asks which barriers were absent, inadequate,...
- FMEA / FMECA
- Failure Mode and Effects Analysis is a bottom-up, inductive method listing what can fail in each component and the effect on the...
- Minimal Cut Set
- In a fault tree, the smallest set of simultaneously failing basic events that is sufficient to cause the top event. Identifies the...
- Root Cause
- The fundamental, underlying deficiency from which the failure originated. Distinguished from immediate cause (the final physical event) and contributing factors. Root-cause analysis...