Quality & Risk
Fault Tree Analysis(FTA)
In one line
Top-down deductive analysis tracing how faults can combine to cause an undesired event.
Definition
FTA per IEC 61025 uses Boolean logic to model how component-level faults and external events combine to cause a defined top-level hazardous event, supporting both qualitative and quantitative analysis.
FTA is a top-down method: it starts from an undesired event, such as overdose delivered, and works down through AND and OR gates to basic causes. It complements bottom-up FMEA by revealing combinations of faults and common-cause failures. In medical devices it is often used for high severity hazards and software-controlled safety functions, and quantitative FTA needs reliable failure rate data.
Why it matters
Often paired with FMEA: FTA reasons backward from a harm; FMEA reasons forward from components. FTA is favored for systems with safety-critical software and rare catastrophic failure modes.
Common pitfalls
- •Failing to clearly define the top-level event can lead to a convoluted and ineffective fault tree.
- •Overlooking common cause failures or human error in the fault tree can significantly underestimate risk.
- •Treating FTA as a standalone activity rather than an iterative part of the product lifecycle reduces its effectiveness.
- •Applying FTA to systems without well-defined failure modes or clear causal relationships can yield misleading results.
- •Not adequately validating the fault tree against real-world data or expert opinion can compromise its accuracy and credibility.
Sources
- IEC 61025 · IEC
- MDIC Case for Quality · MDIC
- FDA - Quality Systems · FDA