In aerospace and other regulated industries it is important to know the exact configuration of a product in the field and to be able to trace parts to each product in which they are used.  

To achieve this it is common practice to utilize part revisions in PLM, and sometimes even in ERP, with the objective of knowing with which part revision a product was built, delivered and is currently operating in the field.

Is it practically possible though to use part revisions to determine the exact as-built, as-shipped and as-maintained configuration of a product?

Before we go to answer this question, it is important to recall two important principles of configuration management:

1. Form, fit and function: The principle of form, fit and function provides that any later revision of a part must maintain their originally intended form, fit and function and thus be able to fully replace all previous revisions of that same part. This principle is explained in detail in our PLM Insight “Form, Fit and Function” (https://plmadvisors.com/form-fit-function/)
   
   
2. Parts and revisions: According to configuration management best practices, a part is identified by a unique identifier (part identification number or PIN) and by the inventory location where it is stored. The revision is not an element of the part identification (MIL-STD-100G, ASME Y14.24M and MIL-STD-961).

Given these two principles, can and should part revisions be used for traceability? Is it possible from a technical and from a business operations point of view, and if yes, what are the benefits and challenges of doing so?

First, let’s look at the technical possibility: Most PLM systems are capable of managing part revisions. Many ERP systems on the other hand are not at all or only partially capable, i.e. some modules support part revisions, some other modules do not. That already creates the first challenge: If parts have revisions in PLM but not in ERP, i.e. the BOM in ERP does not call out a specific part revision, just the part number, how do we know and keep track of what is actually being built on the shop floor and thus delivered to the customer? This is the first breakdown of traceability based on revision.

Secondly, let’s look at traceability from a business operations point of view. Following the second principle of configuration management mentioned above about parts and revisions, parts are only stored by part number in inventory, not by revision. This makes it impossible to determine for certain what part revision was used during the manufacturing process, and hence is the second breakdown of traceability based on revision.

Let’s examine this particular practice in more detail: Let’s say a part is manufactured on a certain date based on the current production released document revision. Let’s further say this part now goes into inventory, where other parts are with the same part number. That is normal business practice. According to configuration management best practices though this new part (or any other part currently in that inventory location) is neither identified with a revision nor with a manufacturing date, i.e. if we look at the part we cannot tell based on what document revision or on what date any part in that inventory location was manufactured.

If now one of these parts is pulled from inventory for manufacturing, or later as a replacement part, nobody at this point can tell what revision this part has or when it was manufactured. Hence when that part is now used in manufacturing or put in in the field, we don’t know what revision it is. Hence it is not generally possible to trace parts by their revision.

Third, let’s look at revision traceability from a process point of view. Even though PLM is capable of managing part revisions, and even if we were able to know exactly which part revision is being used for manufacturing or is replaced in the field requires, it would also require a company to 1) manage Unit BOMs in PLM, and 2) that the services organization also uses PLM and updates the Unit BOM in PLM when a part (revision) is being replaced in the field, or that someone else updates PLM through a tightly integrated process after they get notification from the field that a part has been replaced. There are very few companies today who have such a process in place.

Given these three scenarios, following configuration management best practices it is not generally possible to determine the exact as-built, as-shipped and as-maintained configuration of a product though the use of part revisions. If we need true traceability in the field, we need to use a new part number. Of course we can implement special practices and processes and customize tools to enable revision traceability, but this opens up a host of other challenges, which we will explore in a subsequent PLM Insight.