Spare part
A spare part, service part, or spare, is an item of inventory that is used for the repair or replacement of failed parts. Spare parts are an important feature of logistics management and supply chain management, often comprising dedicated spare parts management systems.
Spare parts are an outgrowth of the industrial development of interchangeable parts and mass production.
Classification
In logistics, spare parts can be broadly classified into two groups, repairables and consumables. Repairable parts are parts that are deemed worthy of repair, usually by virtue of economic consideration of their repair cost. Parts that are not repairable, are considered consumable parts. Consumable parts are usually scrapped, or "condemned", when they are found to have failed.
Economically, there is a tradeoff between the cost of ordering a replacement part and the cost of repairing a failed part. When the cost of repair becomes a significant percentage of the cost of replacement, it becomes economically favorable to simply order a replacement part. In such cases, the part is said to be "beyond economic repair" (BER), and the percentage associated with this threshold is known as the BER rate.
Repair cycle
 | It has been suggested that this article should be split into a new article titled Repair cycle. (discuss) |
From the perspective of logistics, a model of the life cycle of parts in a supply chain can be developed. This model, called the repair cycle, consists of functioning parts in use by equipment operators, and the entire sequence of suppliers or repair providers that replenish functional part inventories, either by production or repair, when they have failed. Ultimately, this sequence ends with the manufacturer. This type of model allows demands on a supply system to ultimately be traced to their operational reliability, allowing for analysis of the dynamics of the supply system, in particular, spare parts.
Repair of repairables
In this model, repairable parts are either repaired by local maintenance capabilities, or sent out for repair by repair providers. Generally, local repair can be accomplish simple repairs faster and with less expense, however, more sophisticated diagnostics and repairs, such as overhauls, require better support equipment that is expensive to deploy to local maintenance facilities. If repair providers are unable to accomplish a repair, the item may be scrapped (or condemned), and replaced. The total time a part spends being repaired is known as the repair cycle time.
Replenishment
Consumable parts short-circuit this process, as they do not allow for repair. Instead of spending time in the cycle waiting for repair, these parts are scrapped directly, and a replacement must be obtained from a supplier. The time it takes for a supplier to provide a replacement part is the lead time.
Performance metrics
Several logistical measures of performance, or performance metrics can be used to evaluate the effectiveness of the repair cycle. Key performance metrics include repair turn-around time, ready rate, fill rate, and system availability.
Commercial
Industrialization has seen the widespread growth of commercial manufacturing enterprises, such as the automotive industry, and later, the computer industry. The resulting complex systems have evolved modular support infrastructures, with the reliance on auto parts in the automotive industry, and replaceable computer modules known as FRUs.
Military
Military operations are significantly affected by logistics operations. The system availability, also known as mission capable rate, of weapon systems and the ability to effect the repair of damaged equipment are significant contributors to the success of military operations. Systems that are not operational due lack of spare parts are said to be "awaiting parts" (AWP), also known as not mission capable due to supply (NMCS).
Because of this, militaries have sought to make their their logistics operations as effective as possible, focusing effort on operations research and optimal maintenance. Maintenance has been simplified by the introduction of interchangeable modules known as line-replaceable units (LRUs). LRUs make it possible to quickly replace an unserviceable (failed) part with a serviceable (working) replacement. This makes it relatively straightforward to repair complex military hardware, at the expense of having a ready supply of spare parts.
The cost of having serviceable parts available in inventory can be tremendous, as items that are prone to failure may be demanded frequently from inventory, requiring significant inventory levels to avoid depletion. For military programs, the cost of spares inventory can be a significant portion of acquisition cost.
In recent years, the United States Department of Defense (DoD) has advocated the use of Performance-based logistics (PBL) contracts to manage costs for support of weapon systems.