The equal apportionment by subsystems allocation method distributes the total failure rate allocation by subsystem. You enter the failure rate or MTBF goal for the top-most assembly, which represents the system. You do not enter weight factors for lower-level items. Instead, the weight factor for a lower-level item is computed using the following equation:

100 / Number of Subassemblies

System Failure Rate Goal: 100 FITs

Subsystem A

Part 1

Part 2

Subsystem B

Part 3

For the top-most assembly (system), you enter a failure rate goal of 100 in its Allocation pane. For more information, see ARINC and Equal Apportionment Methods. No other allocation data is required.

When allocation calculations run, the weight factor is computed for subsystems A and B using the following equation:

System Failure Goal/Number of Subassemblies = Weight Factor

100 / 2 = 50%

The equation for computing the failure rate for subsystem A and B is:

100 * 50% = 50

To compute the weight factors for Parts 1, 2, and 3, the equations below are used.

To compute the failure rates for Parts 1, 2, and 3, the equations below are used.

An example follows with multiple quantities for system tree items. The result is the goal for the quantity listed on that line.

An example follows where parts with non-allocated failure rates are present. Non-allocated failure rates are subtracted out of the failure rate goal.