However, a spares’ benefit should be measured in terms of the projected increase in system availability by adding that spare to the inventory. The system-based inventory provisioning approach is significantly different from the traditional item approach for generating spares requirements, which treats all items the same. In system-based inventory provisioning, spares can then be ranked in terms of benefit, then divided by cost as a measure of the desirability of adding them to the inventory.

The problem then is to answer the question “What mix of spare parts is required to keep the system at some level of operational performance for a specific scenario?”. An optimal solution in this case means a solution in which no other mix of spares can provide a greater system availability for the same cost, or the same system availability for less cost (within the scope of the model assumptions and data). Thus, there exists not just one solution, but a set of solutions that represent different trade-off between system availability and cost.

An example of system-based inventory provisioning is the work on the Aircraft Sustainability Model from the Logistics Management Institute which is a mathematical statistical model used by the United States Air Force to computes optimal spares mixed to support a wide range of possible scenarios. Another example is the D-SIMSPAIR product from D-SIMLAB Technologies which uses simulation-based optimization to compute optimal mix of aerospace rotables for maintenance contracts.

Related Links:

• A systems approach to spares management
• The Aircraft Sustainability Model
• Aircraft Sustainability Model®
• D-SIMLAB Technologies