5. 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.

(Figure 53: Functional Fault Tree in MADE.)

FTA uses symbols to depict the paths to events.

Table 2: FTA Symbols & Terms

Note: the source PDF table interleaves symbol names and definitions in a way that lost strict row alignment during text extraction (the symbol column and definition column appear to have been offset by one row each). The following list preserves all symbol names and all definition text exactly as extracted, in the order given, but exact one-to-one symbol-to-definition pairing should be verified against the live PDF/UI if precision matters:

Symbol/Term list (in source order): AND Gate, OR Gate, Basic Event, Undeveloped Event, XOR Gate, Transfer Gate, K of N Gate, Inhibit Gate, NOR Gate, NAND Gate.

Definitions (in source order):

1. "The next output (failure mode response) occurs if all independent inputs (failure mode response or fault) to this gate occur." — (this matches AND Gate)
2. "The next output (failure mode response) occurs if any independent inputs (failure mode response or fault) to this gate occur." — (this matches OR Gate)
3. "Failure mode or fault of a component or part." — (this matches Basic Event)
4. "A failure mode response in which insufficient information (e.g. failure diagram) is available." — (this matches Undeveloped Event)
5. "A gate that represents the output flow occurs when exactly one of the input flows occurs." — (this matches XOR Gate)
6. "A gate that breaks up the fault tree into separate diagrams whilst maintaining connectivity." — (this matches Transfer Gate)
7. "A gate that represents the output flow occurs only if 'K' of the input flows occurs." — (this matches K of N Gate)
8. "A gate that represents the output flow occurring when the input flow occurs only if a specified condition is also satisfied." — (this matches Inhibit Gate)
9. "A gate that represents the output flow occurs only when none of the input flow/s occurs." — (this matches NOR Gate)
10. "A gate that represents the output flow occurs when not all input flow/s occur." — (this matches NAND Gate)

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.

5.1 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.

Functional FTA is part of the SRA module and is covered in more detail in the SRA Module Guide.

5.2 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.

(Figure 54: Hardware Fault Tree workflow.)

To generate a Hardware Fault Tree:

1. Select View > Open Module > SRA
2. Right-click an item in the Project Explorer
3. Select Fault Tree > Hardware — RBD
   • Alternatively, select Analyses > Fault Tree > Hardware — RBD from the main menu

(Figures 55-57: Accessing the Hardware RBD from the menu; Hardware FTA from main menu; Hardware FTA Creation Window.)