WF54: Mean Time Between Unplanned Maintenance (MTBUM)

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 Unplanned Maintenance (MTBUM) 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. Decision — Weighted Analysis? If Weighted Allocation Type, there are additional values which can be modified; proceed to Step 5. If not, skip to Step 8.
5. Select the component from the table to enable modifiable fields.
6. Assign the appropriate MTBF and MTBUM Prediction value against the selected component.
7. Decision — All components weighted? Repeat Steps 5 and 6 until all component weightings are complete.
8. Select "Calculate" to run the analysis.
9. Review the analysis results.
10. Decision — Do you wish to apply the results to either System Model or an existing MCE analysis?
11. 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, Classic RCM, Maintenance Cost Estimates).
• Step 2: Create New MTBUM Analysis — "Reliability Allocation" dialog, "Create a new Allocation Analysis" page with tabs: Reliability Allocation, MTBUM, MTBCF, MTBF. On the MTBUM tab: "MTBUM Analysis Details" (Name, e.g. "New MTBUM Analysis"; Description) and "MTBUM Analysis" panel (Target Item, e.g. "Power Generation", with Select... button; Allocation Type dropdown, e.g. "Weighted (ARINC)" — described as "The MTBUM of items is allocated according to a weighted distribution amongst the items in their respective level of indenture. The calculations used also 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" — described as "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: "MTBUM Details" (MTBUM Requirement, e.g. 50000.00 hrs; Design Margin, e.g. 10%); "Target Item" panel (Target Item, Allocation Type, Weighting Type — read-only, set at creation); "Run Analysis" panel with Calculate button; "Requirements Verification Tool" panel with "Export Requirement" button. Below, "Weighted Analysis Inputs" table lists Item / MTBF (hrs) / MTBUM Prediction for the hierarchy (e.g. Power Generation 97937.54/97937.54, Control Unit 826044.00/826044.00, Diesel Engine 125000.00/125000.00, Air Filter/Coupling 1/Engine/Governor/Injector Pump/Lift Pump/Primary Fuel Filter/Secondary Fuel Filter all 1000000.00/1000000.00, Fuel Tank with Inlet/Lining/Outlet all 1000000.00/1000000.00).
• Step 5: Select component from Analysis Inputs Table — Click a row in the "Weighted Analysis Inputs" table (e.g. "Air Filter") to select it for weighting.
• Step 6: Assign Weighting Values — "Item Weighting" panel at bottom: Selected Item field (e.g. "Air Filter"), MTBF field (e.g. 80000.00 hrs), MTBUM Prediction field (e.g. 50000.00 hrs). Editing these updates the parent-level MTBF/MTBUM Prediction rollups shown in the table (e.g. Power Generation recalculates to 46060.47/34234.16, Diesel Engine to 51282.05/37037.04).
• Step 9: Review Analysis Results — Click "Calculate" in the Run Analysis panel, then switch to "Analysis Result" tab. "Analysis Results" table with Select All / Deselect All / "Apply to System Model" / "Apply to MCE" buttons, and columns: Item, MTBF (hrs), Maint. to F[ailure ratio], MTBUM Pr[ediction], Maint. Rate, MTBUM W[eighting %], Allocated [values], Allocated F[ailure Rate], Allocated [additional metric]. Example rows: Power Generation (MTBF 46060.47, MTBUM Prediction 34234.16, MTBUM Weighting 90%), Diesel Engine (51282.05 / 37037.04 / 83.19%), Air Filter (80000.00 / 50000.00 / 61.62%), and other items each around 3.08% weighting with MTBF 1000000.00.
• Step 11: Select Applicable Model Items & Apply — In the Analysis Result table, check the checkboxes next to desired items (e.g. Air Filter, Governor, Lift Pump, Primary Fuel Filter checked) then click "Apply to System Model" (or "Apply to MCE") to push the calculated Allocated values back into the model/MCE.

Outputs

• I. Mean Time To Failure: average time a model item will be in operation before failing.