WF40: Create User-defined FTA

Pre-requisites

• SRA Module: access to the Safety and Risk Assessment (SRA) module enables a Fault Tree Analysis (FTA) to be generated.
• FBD Model: defined with functions and functional flows required to map out Fault Tree paths. Inclusion of failure diagrams would improve detail of Fault Trees (see WF06).
• Reliability Data: consists RBD groupings, failure values based on a distribution type and duration of operation.

Detailed Description (numbered steps)

1. Click 'Fault Tree Builder' in 'Fault Tree' under the 'Analyses' tab of the main menu or via the right-click context menu opened on the canvas.
2. Create a new Fault Tree Analysis (FTA) with the green plus icon down the left-hand side of the table. Define a name, description (optional), and P(f) source (baseline or revised), then click 'OK'.
3. Add either of the following event using the right-click Add option: User defined Event, Model based Event, Custom Event, Common Mode Event, Model-based Tree, Transfer Tree.
4. Add events until the structure of the user-defined fault tree analysis is complete.
5. Select a primary event and use the Properties viewer, to review its Event Type and Probability of Failure (P(f)). P(f) value of primary events can either be model-based, user defined (N/A, Direct entry, House Event, Calculated – Lambda).
6. Review all events before reviewing the gates that have been automatically created at event convergence points.
7. Select a gate and use the Properties viewer to review gate type. Gate type can either be OR, AND, K of N, INHIBIT, NOR, NAND or XOR.
8. Review all gates before updating FTA values that also populate the event tables.
9. To calculate FTA P(f) values, either: click 'Calculate Probability of Failure' button in Probability of Failure section, or click 'Calculate Probability of Failure' button in context menu opened on fault tree canvas.
10. Using the 'Event Table Controls' to navigate, review all event tables to confirm accuracy of the FTA.
11. If the FTA is unacceptable, determine where alterations are necessary until it is.

Fields referenced in the diagram

• Create Fault Tree Analysis (FTA): Name, Description, P(f) source
• Add Fault Tree Event: User defined, Model based, Custom, Common Mode, Model based Tree, Transfer Tree
• Review Fault Tree Event Details: Event Code, Narrative, Type, P(f)
• Review Fault Tree Gate Details: OR, AND, K of N, INHIBIT, NOR, NAND, XOR

Decision points

• All Events Added? — No → loop back to Add Fault Tree Event; Yes → Review Fault Tree Event Details.
• All Events Reviewed? — No → loop back to Review Fault Tree Event Details; Yes → Review Fault Tree Gate Details.
• All Gates Reviewed? — No → loop back to Review Fault Tree Gate Details; Yes → Calculate FTA P(f) Values.
• FTA Acceptable? — No → loop back to Add Fault Tree Event; Yes → User-defined FTA Created.

Outputs

• FTA Screen Capture: user-defined FTA fault tree exported as a .png file.
• Raw Data tables: includes Event List Raw Data (exported as .csv), MCSQ Raw Data (exported as .csv), and RI% Ranking Raw Data with inherent Relative Impact (RI) values (exported as .csv).
• FTA Report: Event list & image of the fault tree can be generated from Report Wizard.
• FTA Cut Set Report: Cut set list & inherent images of the fault tree can be generated from Report Wizard.

Screenshot walkthrough (captions/labels extracted)

Step 1: Access Fault Tree Builder

• 'Analyses' menu: Fault Tree (submenu: "Fault Tree Builder" highlighted/tooltip "Open the Fault Tree Builder", Functional, Hardware - RBD), Response Paths, Connection Matrix, Common Mode Analysis, Critical Item Analysis, Criticality & Reliability Editor, Technical Budget Analysis, Failure Rate Prediction (greyed), Markov Analysis (greyed).
• "Fault Tree Builder" tab: left nav Overview / Management. "Fault Tree Analyses" table (Name/Type/Top Event Item/Top Event/Level of Analysis/Reliability Metrics/Created/Modified) empty; toolbar icons JSON Export, Custom Event Library, Preferences.

Step 2: Create Fault Tree Analysis

• "Fault Tree Builder" tab: "Fault Tree Analyses" table with add icon highlighted, tooltip "Create a new Fault Tree Analysis".
• "Fault Tree Analysis" dialog — "Create Fault Tree": "Click OK to create an User-defined Fault Tree." "Analysis Details": Name "New Fault Tree Analysis 1" (editable, highlighted), Description (empty). "Fault Tree Type": "User-defined" (selected), "Model-based Analysis" (with disabled sub-options Propagation Type FCM/Bond, Depth of Analysis Fault/Mechanism/Cause, Level of Analysis "System", Preferred Gate Type "OR"), "Hardware Fault Tree". "Reliability Metrics": "Select the Source for Probability of Failure (p(f)) Values (Applicable for Model-based Events)": Baseline ("Use the original reliability metrics as the source for P(f) values. These values represent the baseline reliability, either manually entered or derived.") / Revised (selected) ("Use the updated reliability metrics that account for maintenance strategy effectiveness. These values reflect the expected reliability after applying Reliability Centered Maintenance (RCM) or user-defined maintenance actions."). Note: "Adjust the default Depth of Analysis at Preferences → Project Preferences → Modeling → Fault Tree Analysis." Buttons OK, Cancel.

Step 3: Add a Fault Tree Event

• Canvas: "Top Event" box (orange) with dashed line down to "+"; context menu: Add... (submenu: Blank Event, Model-based Event, Custom Event, Common Mode Event, Model-Based Tree, Transfer Event), Replace With..., Set a Failure Condition, Calculate Probability of Failure, Reindex Event IDs, Show Additional Information, Cut/Copy/Paste, Delete, Zoom In/Out.
• Canvas result: "Top Event" → "E1" gate → OR-gate icon → "+" → "Basic Event" box → "B2" → circle icon → "+".
• "Add Fault Tree Event" dialog — Model-Based Tree tab: "Select a Failure Mode to add to the Fault Tree as a new Model-Based Tree." Propagation Type FCM (selected)/Bond, Depth of Analysis Fault (selected)/Mechanism/Cause, Level of Analysis "System", Preferred Gate Type "OR". Tree list: Vehicle System > Convert Mechanical - rotational Angular velocity High/Low (Vehicle System) x2 each; Coupling, Driveline, Power Generation, Vehicle.
• Model-based Event tab: tree list of failure modes: Vehicle System > Convert Mechanical - rotational Angular velocity High/Low; Coupling > Couple Mechanical - rotational Torque High/Low; Driveline > Branch Mechanical - rotational Angular velocity High/Low, Cracked, Fractured; Differential > Divide Mechanical - rotational Angular velocity High/Low; Driveshaft; Half Shaft Front > Transmit Mechanical - rotational Torque High.
• Transfer Event tab: "Select an existing Top Event from another Fault Tree to add as a transfer event." Table (Fault Tree Analysis/Top Event/Reliability Metrics): Control Unit FTA ("Brake Control Unit (ABS ECU) Failure", Baseline), Transfer to Wheel Speed Sensor System ("Loss of Wheel Speed Sensor Input", Baseline), Engine Fault Tree Analysis ("Top Event", Baseline), Demonstration Fault Tree Analysis ("Convert Mechanical - rotational Angular velocity Low (Vehicle...", Baseline).
• Custom Event tab: "Create a new or select an existing Custom Event below to add to the Fault Tree." Table (Failure Name/Item Name/Failure Type/Flow Type): "Green Smoke" (Engine #2, Failure Condition), "Burning" (Engine, Fault), "High Torque" (Coupling, Failure Mode, Energy). Note "A new custom event can be created and added to Project Preferences → Modeling → Fault Tree Analysis." Button "New Custom Event >".
• Common Mode Event tab: "Select an existing dependent Common Mode Failure below to add to the Fault Tree." Table (Name/ID / Failure Type / Sub-Type / Source/Error / Failure Condition): Training CMA > New Event 1 > "Item 1" (Design Architecture, Mechanical Property, Flow rate, Loss of output).

Step 5: Review Fault Tree Event Details

• "Properties" panel — "Convert Mechanical - rotational Angular velocity Low (Vehicle System)": tabs General (selected)/Event/Gate. Event ID "E1", Event Code (empty), Name "Convert Mechanical - rotational Angular velocity Low (Vehicle System)", Model-based Name "Convert Mechanical - rotational Angular velocity Low (Vehicle System)", Item "Vehicle System", Narrative (empty).
• "Properties" panel — "Connect Mechanical - rotational Angular velocity Low (Vehicle)": tab Event selected. Event Type dropdown expanded: Basic Event, House Event, "Undeveloped Event" (highlighted/selected). NOT Event checkbox. "Probability": N/A / Direct Entry (Event P(f) 1.00E+00) / House Event (Event Occurred Yes(1.0)/No(0.0)) / "Model-based" (selected): Distribution Type "Exponential", Failure Rate "2.50e-1 per million hours", Exposure Time "9.12e1 hrs"; Calculated (Lambda): Failure Rate "1.00e0 per million hours", Exposure Time "1.0 hours".

Step 7: Review Fault Tree Gate Details

• "Properties" panel — "Branch Mechanical - rotational Angular velocity Low (Driveline)": tab Gate selected. Gate Type dropdown expanded: "OR" (highlighted/selected), AND, K of N, INHIBIT, NOR, NAND, XOR.

Step 9: Update FTA Values

• "Fault Tree - Requires Re-calculation" header (lock icon). "Event Table Controls": Event List/MCSQ/RI% Ranking buttons. "Probability of Failure": RI Type "Birnbaum", P(f) State "Calculation Required" with refresh icon. "Search Events" field. "Report"/"Export" buttons.
• Canvas context menu: "Calculate Probability of Failure", Reindex Event IDs, Identify Repeat Events, Cut/Copy/Paste (disabled), Delete (disabled), Zoom In/Out.
• After calculation: "Fault Tree - Top Event P(f) = 1.00E+00" header (unlocked), same Event Table Controls, P(f) State "Current".

Step 10: Review Event Tables

• "Fault Tree - Top Event P(f) = 1.00E+00": Event List table (ID/Logic/Event Type/Item/Event Name/RI(F)/P(f)): B73-B100 series Basic Events for Primary Fuel Filter (Contaminated/Outgrowth/Blocked/Perforated, RI(F) 0.00E+00, P(f) 2.28E-05 each), Lift Pump (Abraded/Fractured/Scratched/Perforated, 2.28E-05), Lining (Seized/Blocked, 1.52E-05), Inlet (Interference/Pitted/Corroded/Perforated, 3.04E-05), Coupling 1 (Twisted, 4.55E-05).
• MCSQ tab: "Fault Tree - Top Event P(f) = 1.00E+00" — Cut Set table (Logic/RI%/P(f)): Min. Cut Set 1 (B7, 49.84%, 1.00E+00), Min. Cut Set 2 (B6, 49.84%, 1.00E+00), Min. Cut Set 3 (LOW1, 0.25%, 5.00E-03), Min. Cut Set 4 (B22, <0.01%, 9.10E-05), Min. Cut Set 5-18 various (B32, B101, B100, B58, B57, B26, U28, U30, B95, B94) with P(f) values 4.56E-05 to 4.55E-05.
• Event List (second instance): "Fault Tree - Top Event P(f) = 1.00E+00" table (ID/Event Type/Item/Event Name/BIM/FV/P(f)): B6/B7 (Driveline, Fractured/Cracked, BIM 0.00E+00, FV 0.00E+00, P(f) 1.00E+00); B10-B13 (Wheel Rear, Abraded/Fractured/Cracked/Scratched, P(f) 2.27E-05 each); B16-B19 (Wheel Resistance Rear, similar, 2.27E-05); B22 (Planetary Gearbox Rear, Cracked, 9.10E-05); LOW1 (Half Shaft Rear, "Transmit Mechanical - rotational Torque Low (Half Shaft Rear)", 5.00E-03); B49-B58 (Injector Pump, Perforated/Fractured/Scratched/Abraded, 2.28E-05); Governor (Fractured, Open circuit, 4.55E-05 each).