DoD Maintainability Design Techniques (Metric) Handbook

Keywords design techniques DoD handbook maintainability maintainability design techniques metric design


Maintainability requirements, and the resulting maintenance actions, must be supported by system design. Qualitative and quantitative requirements must be established to provide system design guidelines during system development; it is mandatory that a system maintainability concept be formulated prior to detailed design. Identification of maintenance requirements is a key contributor to cost-effectiveness. When life cycle cost is minimized, a major factor is ease of maintenance. Features that facilitate maintainability include the elements of physical attributes, diagnostics, simplification, testability, inspectability, accessibility, and maintainability time/cost design criteria commensurate with the maintainability profile of the system. Each of these elements is considered by the maintainability engineer in his developmetn of concepts, criteria, and technical requirements to assure timely, adequate, and cost-effective support of the design and operational needs of the system. Physical features and pertinent questions that affect maintainability

1. Accessibility. Can the item be reached easily for repair or adjustment?
2. Visibility. Can the item being worked on be seen?
3. Testability. Can system faults be detected readily and isolated to the faulty replaceable assembly level?
4. Complexity. How many subsystems are in the system? How many parts are used? Are the parts standard or special purpose?
5. lnterchangeabiliy. Can the failed or malfunctioning unit be readily replaced with an identical unit with no requirement for alteration and calibration?
6. Identification and Labeling. Are components uniquely identified? Are the labels permanent, or are they easily erased or obliterated by operation or maintenance actions? Are labels positioned to be easily read?
7. Verification. Can it be easily verified that the repaired item is functioning correctly?
8. Simplicity. Is the design as simple as possible? Are standard parts and tools used? Are functions and parts

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Maintainability and reliability are the two major system characteristics which combine to form the commonly used effectiveness index availability. Although reliability and maintainability share co-importance, maintainability merits special consideration because of its influence on system maintenance activities, i.e., the expenditure of man-hours and material, which represent significant budgetary costs over the life of the system. Maintenance activities also reduce the operational readiness of a system.

With the introduction of modern, complex materiel resulting from sophisticated technology and the importance of keeping the materiel combat ready and its potential for higher failure rates and attendant increased maintenance actions, repairs could no longer be based solely on individual judgment and subjective analysis. It became evident that "how much time is required to replace or repair an item” was not the sole criterion rather "how much time and skill are required to determine which item to replace or repair” and how to reduce the need for maintenance or the simplification of the action became equally important. The consideration of maintainability in designing a system is not a new concept systems were always designed to have “good”, “maximum”, or “optimum’’ maintainability. Unfortunately, the use of these qualitative adjectives resulted in an “unknown” maintainability. New techniques, however, permit the conversion of these subjective qualitative judgments into an area of quantitative measurements.

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