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Materiel Availability (Am)

ALCL 082


One of the components of the Sustainment Key Performance Parameter (KPP), defined as the percentage of the total inventory of a system operationally capable, based on materiel condition, of performing an assigned mission. This can be expressed mathematically as the number of operationally available end items/total population.

General Information

In understanding the Sustainment Key Performance Parameter (KPP) for Materiel Availability (Am), the Reliability Key System Attribute (KSA) (or Additional Performance Attribute (APA)), and how both of these relate to requirements for Operational Availability (Ao) it is important for Program Managers (PM) to focus on reliable system designs, effective life cycle support strategies, and adequate testing of these system parameters and attributes. Since testing alone cannot ensure these system parameters, attributes, and requirements will be met by any given system design and support strategy, PMs must understand how system analysis and modeling and simulation (M&S), can help ensure the goals for these parameters, attributes, and requirements are satisfied.

The Joint Capabilities Integration and Development System (JCIDS) ManualManual for the Operation of the Joint Capabilities Integration and Development System, states the Sustainment KPP is mandatory for all programs with a Capability Development Document (CDD).  The JCIDS Manual Annex D to Appendix G to Enclosure B is the "Sustainment KPP Guide," containing detailed information on the KPP (including Am and Ao) and related KSAs and APAs.

Definitions and Methods of Assessment

The DoD definition of Am includes two different formulas. The first is shown below and represents a point (instantaneous) estimate for Am as a measure expressed as a percentage of systems (end items).

figure 1

The key elements that must be incorporated in any assessment of Am are:

  • the total population of systems (end items) 
  • the total life cycle timeframe of the system (end item)
  • all major categories of downtime, both planned and unplanned.

These are the distinguishing features of the Am from the more familiar Operational Availability (Ao) metric (uptime / uptime + downtime).

The recently published update to DoDI 3110.05, Sustainment Health Metrics in Support of Materiel Availability, provides a slightly different method of calculating materiel availability (Am), which, along with operational availability (Ao), it describes as the two superordinate metrics that assess the effectiveness of the DoD sustainment enterprise. Am is still based on the Total Active Inventory (TAI), but in the DoDI is calculated based on available time divided by "possible time" in lieu of the JCIDS Manual calculation based on the number of available end items over TAI.  The DoDI calculation for Ao, like the JCIDS Manual, is time-based, but uses different terms such as "available time" vs. "uptime" and "possible time" vs. "uptime + downtime." As additional policy and guidance updates are published, the differences between these formulas should be resolved. 

Since the definition of Am includes the entire fielded population of systems, the entire system life cycle, and all categories of downtime, it is not possible to obtain a comprehensive estimate of Am from system testing during the Engineering and Manufacturing Development (EMD) or Production and Deployment (P&D) phases of system development (or equivalent phase in other Adaptive Acquisition Framework pathways). System testing, both Developmental and Operational Testing (DT and OT), can be used to obtain data on some of the variables that make up Am, including Mean Time Between Failure (MTBF) and Mean Time to Repair (MTTR). Only after a system has completed fielding and is in the Operations and Support (O&S) phase of its life cycle can data be collected to produce estimates of actual Am. During earlier phases, Am goals and the assessment of a given system's ability to meet those goals must be estimated through analysis. The JCIDS Manual Sustainment KPP Guide (para 3.3.1) includes criteria for evaluation. Those criteria are:

  • Is there evidence of a comprehensive analysis of the system and its planned use, including the planned operating environment, operating tempo, reliability alternatives, maintenance approaches, and supply chain solutions leading to the determination of the KPP value?  Are the analysis assumptions documented?
  • Is the total population of systems being acquired for operational use documented, including those in storage or used for training?
  • Are definitions provided for failures, mission-critical systems, and criteria for counting assets as "up" or "down"?  Are the failure rate values supported by analysis?
  • Does the metric clearly define and account for the intended service life of the total inventory, from initial placement into service through the planned removal from service? (A graphic representation (timeline) of the life-cycle profile is an effective way to present the data.)
  • What is the overall sustainment Concept of Operations (CONOPS)? Is it consistent with Service and Joint Concepts, CONOPS, and/or Operational Mission Summary/Mission Profile, design reference missions, etc. being supported? Is it traceable to the original requirements or agreement with the warfighting community? What alternatives were considered? Have surge/deployment acceleration requirements been identified and are they factors in development of the Am metric?
  • Is failure/downtime defined?  Is planned downtime (all causes) identified and included? Does analysis data support the downtime? Are data sources cited? How does the downtime value compare with downtimes for analogous systems?

Guidance from OSD and the Joint Staff does not mandate specific methods for developing estimates of Am but they do make clear the need for programs to demonstrate the Sustainment KPP goal has been developed based on comprehensive and thorough analysis that considers all factors impacting the Sustainment KPP.  A number of different methods can be used to perform analysis of Am. For low-density systems with simple supply and maintenance concepts, closed-form analytical solutions could be used to develop estimates of Am. For more complex systems with higher densities, modeling and simulation may provide a better analytical method of estimating Am. Stochastic simulation modeling helps overcome some of the problems inherent in making assumptions about the nature of the variables that contribute to Am. Modeling and simulation also allows the program to test various alternative support strategies and, once developed, can continue to be updated and used throughout the system life cycle to provide estimates of Am as fielding plans, operational environments, and deployment requirements change. Even complex, high-density systems can be assessed with modeling and simulation, and these models can often be developed in a reasonable period of time, even with limited resources.

Relationship of Ao to Am

Am is not interchangeable with Ao, which is a separate component of the Sustainment KPP.  While Am applies to the entire fielded inventory of systems, the entire life cycle of the system, and incorporates all categories of downtime such as depot-level maintenance, Ao applies to a limited number of systems within an operational unit and generally does not include systems (end items) that are undergoing depot-level maintenance or are not within the unit's possession. 

This does not mean, however, the two metrics are unrelated. In fact, DoDI 3110.05 refers to the pair as the superordinate metrics that assess the effectiveness of the DoD sustainment enterprise.  A good way to look at the relationship between Am and Ao is to view Am as a function, together with many other variables, of Ao. An adequate Ao is one of the essential building blocks to achieving a high level of availability of total fielded inventory throughout the life cycle of a fielded system. A poor Ao will have a negative impact on Am that will be difficult to overcome regardless of strategies for operational readiness. Since Am can be viewed as a function of Ao, programs need to carefully assess how they establish goals for Am and how these goals relate to program requirements for Ao. Simply using their Ao requirement as the Sustainment KPP Am objective might result in an Am goal that is impossible to achieve. Since Am includes the entire system inventory and life-cycle and all categories of downtime it will usually be difficult for a system to achieve an Am goal that is equal to or higher than an Am requirement defined for a smaller group of systems, shorter time period, and limited categories of downtime. In some cases, however, systems that are very low-density may be able to establish Am goals that are equal to Ao requirements.


Materiel Availability applies to the entire fielded inventory of systems, over the entire life-cycle of the system, and incorporates all categories of downtime. The best way to view the relationship between Am and Ao is to see Am as a function of Ao, together with many other variables. The best way to assess both Am and Ao is through comprehensive modeling and simulation. Materiel Reliability (R) is the cornerstone that insures both Am and Ao requirements can be met. R is far more important in determining the level of availability that is achievable than any other component of product support or system design.