The spare parts module performs evaluation in two modes: regular operation and unsupported mission.

Regular operation During a regular operation, normal spare part replace and repair activities are permitted.

The module takes into account each part’s failure rate and level of repair. The number of systems in the field, operation hours per day, operation days per year, prediction period, and repair turnaround time for Intermediate and Depot levels are taken into account for spare parts evaluation.

Unsupported mission During an unsupported mission, no repair or supply of spare parts is permitted. The only way to restore a system to operating condition is to replace failed parts from existing stock at the operational site. Examples of unsupported missions include submarines at sea, aircraft in the sky, or space shuttles in orbit.

The number of days during which replacement of spare parts is impossible, and the number of systems participating in the mission, are taken into account for spare parts evaluation.