What is the difference between a "major" and "minor" modification? Is there a dollar threshold? Complexity threshold?
The DAU glossary (https://shortcut.dau.mil/JST/dau-glossary) generically defines a modification as a configuration change to the form, fit, function, or interface (F3I) of an in-service, configuration-managed or produced Configuration Item (CI).
Modifications are sometimes bucketed by their purpose. A capability modification alters the F3I in a manner that requires a change to the existing system, performance, or technical specification of the asset. Such modifications are accomplished to add a new capability or function to a system or component, or to enhance existing technical performance or operational effectiveness. A sustainment modification alters the F3I of an asset without changing the existing system, performance, or technical specification of the asset. Such mods correct product quality deficiencies, or bring the asset in compliance with established technical or performance specification(s), and may improve the reliability, availability, maintainability, or supportability, or reduce ownership costs.
Beyond that, the working definition of what constitutes a “minor” or a “major” component modification varies depending on the context, circumstances or whom one might ask. For example, according to the DoD Commercial Item Handbook, there are two types of modifications for commercial items, differentiated by whether the modification is customarily available in the commercial marketplace. The first category is minor modifications customarily seen in the civilian world. And for those modifications not common in the commercial markets, a minor modification means a modification that does not significantly alter the nongovernmental function or essential physical characteristics of an item or component, or change the purpose of a process, while a major modification would be one that does.
As another example, from an aviation perspective, a minor modification is one that has no appreciable effect on the weight, balance, structural strength, reliability, operational characteristics, or other characteristics affecting the airworthiness of the product. A change to any of those characteristics would be a major modification.
Chapter 4 of the Defense Acquisition Guidebook (DAG) (https://shortcut.dau.mil/DAG/CH4) points out that a program may (will!) require modifications to meet emerging requirements, improve performance, address safety issues, reduce operating costs, or extend operational life. Additionally, modern acquisition programs are dependent on technology and thus may require technology refresh and insertion at a higher rate than legacy systems. Such modifications may vary from simple component replacement, to an MDAP-sized investment.
As a program or system matures, the PM executes an acquisition strategy that considers how a modification will be implemented - remaining production units only, retrofitted into fielded units, or implemented on an attrition basis as supply is replenished. In all cases, the program manager should analyze the potential impacts to readiness and cost of maintaining multiple configurations. Planning considerations include urgency of the modification, impact to ongoing operations, manufacturing lead times, production rates, skill levels, training and tooling required, maintenance level of incorporation (i.e., OMA, IMA or OEM/Depot), and potential impact of each of the other Integrated Product Support Elements (IPSE).
The PM develops the product support package required to implement the change (for example, installation instructions, and training) and plans for changes needed to the original system’s product support package to support the change once implemented. Depending on impact of the modification, the PSM may need to update the LCSP. Examples of modifications that would likely drive an update to the LCSP include changes in reliability, significant increases or decreases in funding required to support the change, changes in level of repair, or major changes in CONOPS. Except for pointing out the wide variation in system modifications that may take place, the DAG does not provide much guidance as to how to characterize those modifications. Speaking broadly, across DOD a typical definition of a minor modification would be one that does not alter F3I, nor appreciably impact expected performance, reliability or maintainability. The Sd-22, Diminishing Manufacturing Sources and Material Shortages (DMSMS), (https://shortcut.dau.mil/JST/dmsms-guidebook) would probably define this as a Simple Substitute - the item is replaced with an existing item that meets all requirements without modification to either the item or the next higher assembly (NHA) and requires only minimal qualification. Typically, this implies use of a commercial item or non-developmental item that is a fit/form/function substitute. Associated costs are largely administrative, and this is sometimes referred to as an alternate component.
A major modification might be one that does impact any of those cited factors or one that required some change or different operation of the NHA, what the SD-22 might call a ‘redesign’. Of note – the same document reminds us to consider obsolescence and DMSMS issues ANY time we are planning a modification, an Engineering Change Proposal (ECP) or a an upgrade/tech refresh, in order to avoid or minimize the scope of DMSMS-related, and more expensive out-of-cycle redesigns.
The DAG specifically tasks program managers with collecting and analyzing actual field data to evaluate and justify potential design modifications to achieve reliability and maintainability goals and/or to further reduce sustainment costs. This is because we KNOW mods and tech refresh are an unavoidable fact of life for DOD weapons systems, a key part of the Sustaining Engineering (SE) Integrated Product Support Element (IPSE). There are many references that direct preparation for and execution of mods, but how they are characterized will depend typically on the program manager or Milestone Decision Authority (MDA). At program initiation, a program office will have a charter with the MDA which basically spells out what decisions in this arena are the purview of which of the two decision makers. Thresholds for overall cost, budget, impact, risk, etc., for a given program determine if it is a “minor” change or a “major” change, under MDA or PM decision authority. Some mods are of such magnitude that an MDA will designate them as new standalone programs.
For the most part, whether a modification is designated as a minor or a major change will be up to the program manager and chain of command, and likely a function of risk, costs and budget, and the acquisition strategy, among myriad other factors unique to each instance.
The “Technology Refresh” ACQuipedia article (https://shortcut.dau.mil/acq/tech_refresh) provides further information on mods and their context, for example a reminder that configuration management principles of the MIL-HDBK-61A, “Military Handbook: Configuration Management Guidance”, are important for equipment changes. Additional information on this critical aspect of configuration management include: