4 Accessing the Reliability Allocation Editor

To access this tool, select Analyses > Reliability Allocation editor from the main menu.

Figure 5 shows the Analyses menu with: Fault Tree, Response Paths (submenus), Connection Matrix, Common Mode Analysis (greyed out), Critical Item Analysis (greyed out), Criticality & Reliability Editor, Technical Budget Analysis, Failure Rate Prediction, Markov Analysis, RBD Analysis, Reliability Allocation Editor (highlighted), Back-Fit RCM (greyed out), Model-based RCM, Maintenance Cost Estimates.

Figure 6 shows the "Reliability Allocation" editor's Overview/Management view: a list of existing analyses (RA Analysis 2, RA Analysis 3) each with Target Item, Analysis Type, Target/Require... value, Type, Created date (e.g. "RA Analysis" → Vehicle System → Reliability Alloc... → 0.9 → Equal → March 20 2026, 09:20...; "RA Analysis 3" → Power Generation → 0.95 → Weighted (AGREE) - State...; "RA Analysis 2" → Diesel Engine → 0.7 → Weighted (AGREE) - Func...), with a "Reliability Allocation Analysis Details" panel on the right showing Name, Description, Target Item (Vehicle System), Allocation Type (Equal, with helper text: "The reliability of items is allocated equally amongst the items in a level of indenture to satisfy the Target Reliability of the parent item. The calculations used depend on the type of RBD Group."), and a Mission Profile Definition section (Mission Profile: Long Trip, Duration: 5.211 hr (5.211 hours), Mission Cycles: 4.00, Σ Total: 1792.00 Kilometers, Description: "A short duration trip for the vehicle, assuming a benign environment and low operational loading.").

5 Reliability Allocation Methods

The following sections describe the differences between current RA analysis methods.

5.1 Equal Allocation Method

The Equal Allocation Method calculates Reliability Allocation based on an evenly distributed approach where items in a level of indenture are allocated equal reliability in order to satisfy the target reliability of the parent item. For example, each sub-system will have reliability attributed such that the total system reliability is met. As a result, lower levels of hierarchy require higher reliabilities to achieve the total system reliability. A factor that influences this method is the presence of RBD groupings.

5.2 Weighted Allocation Method

5.2.1 AGREE Method

The reliability of items is allocated in a weighted distribution amongst the items in a level of indenture to satisfy the Target Reliability of the parent item. The calculations used depend on the type of RBD Group. The three main weighting factors are described in the table below.

Table 1: RA Weighting Types and Descriptions

Weighting Type	Description
State of the Art	Rank the item based on its State of the Art. A more highly developed item is given a higher ranking than a less developed item. Items with higher State of the Art are assigned relatively lower reliabilities than other items on the same level of indenture.
Hardware Complexity	Rank the item based on the Hardware Complexity. A more complex item is given a higher ranking than a less complex item. Items with higher Hardware Complexity are assigned relatively lower reliabilities on the same level of indenture.
Functional Complexity	Rank the item based on the Functional Complexity. A more complex item is given a higher ranking than a less complex item. Items with higher Functional Complexity are assigned relatively lower reliabilities on the same level of indenture.

5.2.2 ARINC Method

The reliability of items is allocated in a weighted distribution amongst the items in a level of indenture to satisfy the Target Reliability of the parent item. The calculations used depend on the type of RBD Group. The weighting factor is described in the table below.

Table 2: RA Weighting Types and Descriptions

Weighting Type	Description
Historical Reliability Data	Weighting is automatically calculated based on the relative current MTTF values in the system model.

Analysis Exercise (from the guide): Generate a RA analysis for the Vehicle System using the Equal Allocation method with a 90% Reliability Target and apply the analysis results to all items in the Vehicle System.

6 Overview/Management Page

The Overview/Management page displays all existing RA analyses in a table, including their associated information such as RA analysis type, Mission Profile data, Target Items, and descriptions.

To create a Reliability Allocation analysis:

• Select the plus symbol.
• From the dialog, enter the RA analysis name and description.
• Select the Target Item and Analysis Type (currently Equal or Weighted).
  • If Weighted is selected, further select Weighting Type (State of Art or Hardware Complexity or Functional Complexity or Historical Reliability Data).
  • Selection must be completed before selecting mission profile. It does not allow mission profile to be selected unless the target item is selected.
• Select the appropriate Mission Profile from the drop-down menu.
• Select OK to close the dialog and create the analysis tab.

To create a copy of an existing RA analysis:

• Select a RA analysis from the table.
• Select the copy symbol.
• The editor will automatically generate a copy of the selected RA analysis and open the copied analysis in a new window within the RA editor.

To open an existing RA analysis:

• Select a RA analysis from the table.
• Select the open symbol.
• The editor will automatically open the RA analysis in a new window within the RA editor.

To delete an existing RA analysis:

• Select a RA analysis from the table.
• Select the delete symbol.
• A pop-up dialogue will ask to confirm RA analysis delete.
• Select 'OK' to confirm delete.

Figure 7 ("Dialog for Creating a New RA") shows the "Reliability Allocation" creation dialog with tabs: Reliability Allocation, MTBUM, MTBCF, MTBF. On the Reliability Allocation tab: "Reliability Allocation Analysis Details" (Name, Description), "Reliability Allocation" (Target Item: Vehicle System, with Select... button; Allocation Type: Equal, with helper text describing the Equal method), "Mission Profile Definition" (Mission Profile, Duration, Mission Cycles, Σ Total, Description fields).

Figure 8 ("RA Configuration Page for Equal Allocation") shows the Analysis Configuration tab: "Target Reliability" radio options (0.9999999 / 0.95 / 0.9 [selected] / Custom), "Target Item" (Power Generation, Allocation Type: Equal — both fixed and cannot be changed), "Run Analysis" (Calculate button), and "Requirements Verification Tool" (Export Requirement button, to create a Reliability Allocation requirement in the Requirement Verification Tool).

Figure 9 ("RA Configuration Page for Weighted Allocation") shows an example for target item "Diesel Engine", Allocation Type = Weighted (AGREE), Weighting Type = Functional Complexity, Target Reliability = Custom 0.7. Below, a "Weighted Analysis Inputs" table lists items (Diesel Engine > Air Filter, Coupling 1, Engine, Governor, ...) each with a Reliability column (e.g. Air Filter 0.9992715, Coupling 1 0.9999089, Engine 0.9999089, Governor 0.9999089) and a Functional Complexity column (default value 1.0* for most, N/A for Air Filter — asterisk indicating "default value is being used"). An "Item Weighting" section shows the selected item (Diesel Engine) with a Functional Complexity slider ranging 1.0 to 10.0 (currently at 1.0), with helper text: "Rank the item based on the Functional Complexity. A more complex item is given a higher ranking than a less complex item. Items with higher Functional Complexity are assigned relatively lower reliabilities on the same level of indenture."

Note: The RA Analysis Configuration page will contain additional sections depending on the type of RA analysis selected. For example, Weighted RA analysis based on Functional Complexity will have an Item Weighting section.