Chapter 3 - Maintainability Measures, Functions, and Models

Abstract

One way to define the difference between reliability and maintainability is that while reliability is the probability that a failure will not occur in a particular time, maintainability is the probability that required maintenance will be successfully completed in a given time period. Maintainability is a design characteristic that affects accuracy, ease, and time requirements of maintenance actions. Reliability and maintainability are important measures of the effectiveness of systems or products. It may be measured by combining factors, such as frequency of maintenance, maintenance costs, elapsed maintenance or repair times, and labor hours. These measures make possible the quantitative assessment of product maintainability. The primary purpose of maintainability measures is to influence design and subsequently produce a more cost-effective and maintainable end product. The measures used in maintainability analysis include mean time to repair (MTTR), mean active preventive maintenance time, and mean active corrective maintenance time, maximum corrective maintenance time, and mean maintenance downtime. MTTR measures the elapsed time required to perform a given maintenance activity and is subsequently used to calculate system availability and downtime. The objective of a preventive maintenance program is to postpone the point at which the equipment or any of its components wears out or breaks down. A carefully planned preventive maintenance program can help to reduce the equipment's downtime and improve its performance.