Title: One for One Replacement of Main and Sub Components
Author: James Peterson
Company: Lockheed Martin
Phone: (972) 603-0394
Department of Defense (DoD) maintenance facilities typically have three main constraints: Schedule, Budget and Parts Availability, which by nature, have a negative domino effect to production. The first constraint is Parts Availability. In the maintenance environment an aircraft, for example, arrives at the facility and is then cleaned, stripped down to its bare bones and its components are sent through the various shops for further teardown and inspection. Some items based on historical depot overhaul factors (DOF) are automatically replaced, while others may have a lower replacement trend due to repairability or expected lifespan. For those that are automatically replaced, there is typically stock on hand at all times based on the number of scheduled aircraft to be completed within the fiscal year. For those that are not replaced automatically, there is typically a low number of new parts kept on site or there is a generic forecast established with suppliers which generally lowers the lead times to order and have them shipped to the facility(ies).
The parts that fall into one of the above categories are unlikely to cause any delays to the master schedule or to the overall budget, however, there is a subset of main and sub-components that require extensive teardown, multiple testing, and multiple inspections at which times they can fail and/or be deemed irreparable. These are the ones that cause the most disruptions and have the biggest impact on Schedule, Budget and Part Availability. These main and sub-components (once removed from the aircraft) are sent to cleaning, then they are disassembled, and the sub-components are sent to the various specialty shops for further cleaning, inspection and repair. By this point, the component has accumulated a large number of man-hours spent on the various operations and until each sub-component has been inspected and returned to serviceable condition, the parts are still subject to potential fallout/failure.
If failure occurs then the item is then placed on order and subject to lead-time plus costs associated with ordering the replacement, including expedite fees. We must also account for the cost of man-hours and other resources that have already been spent on the component prior to its failure and the overtime hours that will be spent on the aircraft to bring it back on schedule once the material arrives.
To address this significant problem, we can order a set number of new components and store them as “Safety Stock” until the first aircraft is ready for its installation. The removed component would be sent through the various shops as normal but instead of the aircraft having to wait for the removed component to be made serviceable, it will instead receive the new component. This is repeated until the components in the repair cycle are made serviceable and the inventory has reached the optimal “Safety Stock” level. With this approach the facility maintains schedule reliability, expedite fees are virtually eliminated, overtime hours are drastically reduced, and the military maintains their fleet readiness.