6. Fault Tree Analysis (FTA)

Fault Tree Analyses (FTA) provides a top-down, deductive failure analysis in which a perturbed system state is analyzed. This analysis determines the probability and relationship of failure responses between items. MADE provides hardware (RBD) fault tree and functional (FCM) fault tree diagrams.

A Fault Tree displays event-based characterization of a system, with multiple paths to possible events listed from a top-down view. While FMEA is considered a bottom-up approach, a Fault Tree gives the user a global view of events that could happen and the paths that allow these events.

FTA uses symbols to depict the paths to events (partial list recovered from Table 5, "FTA Symbols & Terms" — this SRA guide's table extraction was truncated relative to the fuller symbol list found in the RAM Module Manual's equivalent table):

Term	Definition
AND Gate	The next output (failure mode response) occurs if all independent inputs (failure mode response or fault) to this gate occur.
OR Gate	The next output (failure mode response) occurs if any independent inputs (failure mode response or fault) to this gate occur.
Basic Event	Failure mode or fault of a component or part.
Undeveloped Event	A failure mode response in which insufficient information (e.g. failure diagram) is available.

(Note: the RAM Module Manual's equivalent FTA symbol table additionally lists XOR Gate, Transfer Gate, K of N Gate, Inhibit Gate, NOR Gate, and NAND Gate — see ram-fault-tree-analysis.md for the fuller symbol/definition set, as this SRA guide excerpt did not extract those additional rows.)

Functional & Hardware Fault Trees consider two parameters:

• Probability of Occurrence (P(f)) — refers to the likelihood or relative rate that a fault or event (failure response) will occur.
• Relative Importance (RI%) — the importance of an event compared to the other system events. Events with higher reliability have a lower relative importance.

Note: When generating a fault tree, MADE provides the ability to select baseline or revised P(f) for the events. Baseline P(f) refers to inherent P(f), whereas revised P(f) considers the effectiveness factor of the control measures defined (i.e. maintenance actions) to reduce/mitigate the event from occurring.

6.1 Functional Fault Tree Analysis

A Functional Fault Tree depicts the system failure responses and the paths that can cause failure events based on the functional dependencies established in the FBD model. Failure events are created by multiple failure modes across various items. Cut Sets provide the ability to view specific system failures when large amounts of failure paths are created in a Functional Fault Tree.

Note: MADE includes the ability to generate FTA based on the MADE model (model-based FTA) or create custom FTAs. This section discusses model-based FTA.

To generate a Functional Fault Tree:

1. Right-click an item in the Project Explorer
2. Select Fault Tree > Functional
   • Alternatively, select Analyses > Fault Tree > Functional from the main menu

To create a model-based FTA for a chosen Top Event (End Effect):

1. Click the New/Create icon in the Overview/Management tab
2. Enter Name and Description for the analysis
3. Select Fault Tree Type:
   • Select Model-based Analysis
   • Select the depth of analysis (fault/mechanism/cause)
   • Select Level of analysis (system or component/subsystem)
   • Select Preferred Gate Type (OR, AND, or K/N)
4. Select Reliability Metrics (baseline P(f) or revised P(f))
5. Select the desired system failure in the Top Event section
6. Click OK

To view the effects (P(f)) of the events on the chosen Top Event:

• Click the calculate icon to calculate the P(f) of each event

To view a cut set:

1. Select the MCSQ button
2. Select a Cut Set from the table
3. Verify that the fault tree has been filtered to a single failure path

Exporting Fault Tree information

Fault Tree information can be exported in two ways:

• Select the Export to CSV icon to export all table data to a CSV file
• Select the Capture Screen icon (alternatively, View > Capture Screen) to export the fault tree as a PNG image

6.2 Hardware Fault Tree Analysis

The Hardware Fault Tree depicts the system from a hardware perspective and represents the reliability groups defined in the RBD editor. The Hardware Fault Tree will show the dependencies of the items/groups and the effect of the failure on the top effect.

Hardware FTA is part of the RAM module and is covered in more detail in the RAM Module Manual (see ram-fault-tree-analysis.md).