Handbook of Systems Engineering and Management. Ed. Andrew P. Sage and William B. Rouse. 2nd ed. Wiley-Interscience, New York, NY, pp. 361-95, 2009

Reliability, Maintainability, and Availability

Michael Pecht
Center for Advanced Life Cycle Engineering (CALCE)
University of Maryland
College Park, MD


Reliability, maintainability, and availability (RMA) engineering is a discipline in which data are gathered and models are formulated to make decisions concerning system failure, operational readiness and success, maintenance and service requirements, and the collection and organization of information from which the effectiveness of a system can be evaluated and improved. RMA engineering thus includes engineering design, manufacturing, testing, and analysis. RMA metrics can be considered to be characteristics of a system in the sense that they can be estimated in design, controlled in manufacturing, measured during testing, and sustained in the field (Pecht, 1995).

When utilized early in the concept development stage of a system’s development, RMA serve to determine feasibility and risk. In the design stage of system development, RMA analysis involves methods to enhance performance over time through the selection of materials, design of structures, choice of design tolerances, manufacturing processes and tolerances, assembly techniques, shipping and handling methods, and maintenance and maintainability guidelines. Engineering concepts such as strength, fatigue, fracture, creep, tolerances, corrosion, and aging play a role in these design analyses. The use of physics-of-failure concepts coupled with the use of factors of safety and worst case studies are often required to understand the potential problems, trade-offs, and corrective actions. In the manufacturing stage of a system, RMA analysis involves determining quality control procedures, reliability improvements, maintenance modifications, field testing procedures, and logistics requirements. In the system’s operational phases, RMA involves safety inspection, failure analysis, maintenance, and logistical support.

It has been well documented that while the costs incurred during the concept and early design stages of a system development cycle are about 5–8% of the total costs, these stages affect over 80% of the total system costs. For purposes of cost-effective and timely system development, RMA engineering is virtually non-effective if implemented at the completion of the design phase. The earlier a potential event is addressed, the more prepared the engineering team can be to correct or alleviate potential problems.

When a system is being designed, it is assumed that the required investment will be justified according to how well the system performs its intended function over time. This assumption cannot be justified when a system fails to perform upon demand or fails to perform repeatedly. For example, it is not enough to show that a computer can conduct a mathematical operation; it must also be shown that it can do so repeatedly over its expected life. Furthermore, higher life-cycle costs and stricter legal liabilities have also made system RMA considerations of greater importance. As the attitude toward production of engineering systems has changed, RMA engineering has established itself as one of the key elements when designing, manufacturing, and operating a system.


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