Part Chain
A Part Chain is series of revised part numbers, each superceding the previous revision of that part.
• As you trace the historical chain of supercession, you are looking "down-chain".
• As you look forward at the string of progressively newer revisions toward the current revision of the part, you're looking "up-chain".
For example, given a chain of Parts A, B, C, D with part D being the latest part in the chain, Part D is up-chain of A, B and C and Part C is up-chain of B and A.
In a typical service support environment, it is not unusual to have more than one part that will satisfy a functional need either with respect to multiple revisions of the same part or with separate part numbers that have identical form, fit and function. It is also likely that a specific replacement need may be met with one or more higher-level assemblies. Each of the valid FRUs that might be used to satisfy a requirement may be available or unavailable at the specific time of need, and the actual replacement decision is driven by factors such as cost, time to repair or accessibility. Part chains describe a series of hierarchical relationships between parts that may satisfy the same need.
In part chains there are two different relation types:
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Relation Type
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Description
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Alternate Relation Type
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Within part supercession chains, an up-chain part can be used alternatively for the referenced down-chain part (but not vice versa). For example, newer revision B can be used when older revision A has been burned off, but older revision A may NOT be used to meet a need for newer revision B. Flagging a superseded part as having an Alternate allows existing inventory of this superseded part to be fully leveraged before moving up-chain to the newer part. It also allows planning for the older part to make use of some of the newer part's Safety Stock in an emergency, if that does not disrupt planning of the newer part by triggering an order.
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Replace Relation Type
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On part supercession chains, a newer (up-chain) part has replaced an older part. The older part will no longer be planned, and will, therefore, be removed (or "burned off") from every stocking location's ASL during the next AutoPilot run. Future demand for replaced parts is redirected to the next up-chain planned part (Top Most Part or Alternates). Inventory may optionally be rolled up-chain only if it is interchangeable for planning purposes with the inventory of the up-chain part. Three flags are available to specify whether inventory can be rolled up. If changes between the older part and the newer part are minor or have no impact on their functionality, then Roll Up Good and/or Roll Up Bad flags can be set to "Yes" to combine (for planning purposes) the inventory of the older part with that of the newer part at each stocking location. Setting these flags to "Yes" thus creates a "two-way" compatibility between the older part and the newer part. Likewise, if repair centers can upgrade the older part to the newer part, the "roll up good as bad" flag can be set to "Yes" within the Replace relationship.
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A part can only belong to one part chain for a location. However, locations can have many part chains.
See also