Support concepts are the methods, including the maintenance concept, by which the customer intends to maintain the product and can be as varied as the design itself. Support concepts range from discard at failure to a complete overhaul at failure. They may include periodic or scheduled maintenance or overhaul. They can include maintenance performed by the customer, the supplier, a third party, or some combination of the three. Within the military services, three levels of maintenance are normally defined: organizational (on-site), intermediate (local shops), and depot (an overhaul facility). (No one definition of maintenance levels could be found for all commercial industry. However, perhaps defined somewhat differently or combined in some way, the following levels of maintenance are considered representative of those used by commercial industry). Maintenance performed at these levels keeps the product serviceable or restores it to an operational condition after a failure. A brief description of each level of maintenance follows.
Organizational Level of Maintenance. Organizational
maintenance is performed at the operational or product site. Maintenance at
this level normally is limited to periodic performance checks, visual
inspections, cleaning, limited servicing, adjustments, and removal and
replacement of some components (i.e., constituent module, part, item, etc. of
the product). Repair of removed components is normally not made at this level
(but see 18.104.22.168.2 ). Instead, the failed component is replaced with a spare. The removed component is then sent to the next level of maintenance (usually intermediate) for repair. Diagnostics, accessibility and ease of removal and replacement are very important at the organizational level and should be key design considerations. This level of maintenance has the primary goals of keeping the product in a
serviceable condition and rapidly restoring the product to an operable condition after failure using low to moderately skilled personnel.
Intermediate Level. Intermediate level maintenance is normally performed at a "shop location" and may be performed on the product or a repairable component of the product. At this level, products might be repaired by removal and replacement of parts or modules, or the parts or modules of a product might be repaired. The skill level of personnel at this level is usually higher than at the organizational level of maintenance. Intermediate level of repair facilities may also be tasked with doing limited depot/overhaul level repairs. These type of repairs are typically based upon technical knowledge, facilities and potential cost savings.
Depot Level. Depot is the highest level of maintenance. The depot is a specialized repair facility that may very well be structured like an assembly line. It may be a customer-operated repair facility or the original equipment manufacturer's plant. Maintenance includes rebuilding or overhauling a product and may be performed on a specific lot of failed equipment that has been screened for similarity in failure type. The most highly skilled and trained technical personnel are assigned to depots. Test equipment is very complex, technical publications are more detailed, and manufacturing source data are frequently available. One specific depot might be structured to support all forms of communication radios or all types of pumps.
Maintenance can include two basic types of tasks. The first, called preventive maintenance (PM), is usually performed at the organizational level.
PM retains a product in serviceable condition by inspections, servicing and other preventive measures performed on a calendar, cyclical, or on-condition basis. The second is corrective maintenance (CM). CM is performed to return a product to operation after a failure and may be accomplished at the operational, intermediate, or depot level. The cost of maintenance, preventive or corrective, is directly determined by the maintainability of the design.
A support concept is more than simply identifying
whether PM and CM are required and whether maintenance will be performed at
one, two, or three levels of organization. It means deciding on a
run-to-failure or on-condition maintenance approach (see 22.214.171.124 ). It also addresses whether support will be provided by the customer, by the product manufacturer, or by both. Often, the military services elect to plan for contractor support at the intermediate and depot levels until a product has been proven in actual use. Then responsibility for the maintenance may be transitioned to the military service. Such a strategy is called interim contractor support. Finally, a support concept can involve centralizing some organizational and intermediate level maintenance at one or two sites.
The approach to handling ambiguity groups is also a part of the support concept. Sometimes, factors make fault isolation to a single replaceable unit or item impossible to achieve. These factors include the complexity that would be added by fault isolating to a single item, the total cost associated with fault isolating to a single item compared with the cost associated with fault isolating to two or more items, and the type of technology being used. Consequently, some failures will be detected by the integrated diagnostics and isolated to two or more items. To correct the failure, one of two basic approaches may be used. For relatively small ambiguity groups, the entire group will be replaced. For larger groups, items in the group will be iteratively replaced until the failure is corrected. The decision to use group or iterative replacement is primarily based on economics and the effect on predicted total downtime.
The support concept should be tailored to the type of product in question. That is, the product may be a new development, a
non-developmental item, or a commercial off-the-shelf (COTS) item. In the first case, planners have a good deal of latitude in selecting the concept, since the designers can respond to the chosen concept as they design the product. For non-developmental items, less latitude is available. Finally, for COTS, little flexibility in choosing a support concept is left to the planners. It is unlikely that the engineering, design, and other detailed data needed to develop an organic repair capability will be available. Also, configuration control below the product level will most likely be maintained by the supplier, not the customer. So in many cases, support for COTS will consist only of removal and replacement at the operational level with depot and even intermediate maintenance performed by the depot.
For new development products, the support concept can and should greatly influence the design for maintainability. For example, ease of disassembly is not a concern for non-repairable products that are thrown away after failure. But if the product is a component or subsystem of a larger product, accessibility to facilitate removal and replacement is important. Also, the design approach for a product can be very different depending on whether the customer or the contractor will be providing the support.