WF55: Mean Time Between Critical Failure (MTBCF)

Pre-Requisites

• A. RAM Module: access to Reliability, Availability & Maintainability (RAM) module enables Reliability Allocation.
• B. MADE Project: consists of FBD model items further defined with MTTF values.

Detailed Steps

1. Access Reliability Allocation (RA) Editor under 'Analyses' in the main menu bar.
2. Select the 'Plus' icon to create a new Mean Time Between Critical Failure (MTBCF) Allocation Analysis and define the analysis details (Analysis Name, Description, Target Item, Allocation Type) accordingly.
3. Set the Target Requirement and Design Margin by entering values in the text fields.
4. Select the component from the table to enable modifiable fields.
5. Assign the appropriate MTBF value and Mission Critical status against the selected component.
6. Decision — Weighted Analysis? If Weighted Allocation Type, there is an additional factor to be applied; proceed to Step 7. If not, skip ahead.
7. Assign Criticality Factor to selected component.
8. Decision — All components weighted? Repeat Steps 4 to 7 until all component weightings are complete.
9. Select Calculate to run the analysis.
10. Review the analysis results.
11. Decision — Do you wish to apply the results to either System Model or an existing MCE analysis?
12. Select model items from the Analysis Results table to apply the results to the system model or an existing MCE. Select the "Apply to System Model" or "Apply to MCE" button to apply the calculated results to either System Model or MCE respectively.

Screen-by-screen detail (from embedded screenshots)

• Step 1: Access Reliability Allocation — Main menu: Analyses > Reliability Allocation Editor (alongside Fault Tree, Response Paths, Connection Matrix, Common Mode Analysis, Critical Item Analysis, Criticality & Reliability Editor, Technical Budget Analysis, Failure Rate Prediction, Markov Analysis, RBD Analysis, Back-Fit RCM, Model-based RCM, Maintenance Cost Estimates).
• Step 2: Create New MTBCF Analysis — "Reliability Allocation" dialog, "Create a new Allocation Analysis" page, tabs: Reliability Allocation, MTBUM, MTBCF, MTBF. On MTBCF tab: "MTBCF Analysis Details" (Name e.g. "New MTBCF Analysis", Description) and "MTBCF Analysis" panel (Target Item e.g. "Power Generation" with Select... button; Allocation Type dropdown e.g. "Weighted (ARINC)" — described as "The MTBCF of items is allocated in weighted distribution amongst the items in a level of indenture based upon their Criticality Factor to satisfy the MTBCF Requirement of the parent item. The calculations used depend on the MTTF of the items which can be modified within the context of this analysis."; Weighting Type dropdown e.g. "Historical Reliability Data" — "Weighting is automatically calculated based on the relative current MTTF values in the system model."). Click OK.
• Step 3: Enter Analysis Parameters — "Reliability Allocation" editor, tabs Analysis Configuration / Analysis Result. In Analysis Configuration: "MTBCF Details" (MTBCF Requirement e.g. 50000.00 hrs, Design Margin e.g. 10%); "Target Item" panel (read-only Target Item, Allocation Type, Weighting Type); "Run Analysis" panel with Calculate button; "Requirements Verification Tool" with "Export Requirement" button. Below, "Weighted Analysis Inputs" table with columns Item / MTBF (hrs) / Mission Critical? / Criticality Factor (%) — example values: Power Generation 97937.54/No/N/A, Control Unit 826044.00/No/100%, Diesel Engine 125000.00/No/N/A, Air Filter through Secondary Fuel Filter all 1000000.00/No/100%.
• Step 5: Assign Weighting Values — "Item Weighting" panel at bottom: Selected Item (e.g. "Air Filter"), MTBF field (e.g. 500000.00 hrs), "Mission Critical?" Yes/No radio buttons (set to Yes in example), "Criticality Factor (%)" field/slider (e.g. 100.0%). Changing these updates parent-level rollups in the table (e.g. Power Generation MTBF becomes 89201.38, Mission Critical Yes; Diesel Engine 111111.11, Yes).
• Step 7: Assign Criticality Factor — Same "Item Weighting" panel — the "Criticality Factor (%)" slider/field (e.g. set to 100.0) determines how the item's contribution to the MTBCF requirement is weighted.
• Step 10: Review Analysis Results — Click "Calculate", then view "Analysis Result" tab. Table columns: Item, MTBF (hrs), Mission Critical, Criticality Factor, Critical Failure [Rate], MTBCF Weigh[ting %], Allocated Failu[re Rate], Allocated MTT[F]. Example rows: Power Generation (MTBF 89201.38, Mission Critical Yes, MTBCF Weighting 90%, Allocated Failure 12.4218, Allocated MTTF 80503.38), Control Unit (826044.00, No, 9.72%, 1.2106, 826044.00), Diesel Engine (111111.11, Yes, 72.25%, 10.2112, 97931.21), Air Filter (500000.00, Yes, Criticality Factor 100%, Critical Failure 2.00, MTBCF Weighting 16.06%, Allocated Failure 3.2112, Allocated MTTF 311405.26), remaining items each ~8.03% weighting with MTBF 1000000.00.
• Step 12: Select Applicable Model Items & Apply — In Analysis Result table, check desired items (e.g. Air Filter, Engine, Primary Fuel Filter checked) then click "Apply to System Model" or "Apply to MCE".

Outputs

• I. Mean Time To Failure: average time a model item will be in operation before failing.
• II. Mission Critical: indication on component of Mission Critical or not.