Handbook of Reliability, Availability, Maintainability and Safety in Engineering Design - Part 42 studies the combination of various methods of designing for reliability, availability, maintainability and safety, as well as the latest techniques in probability and possibility modelling, mathematical algorithmic modelling, evolutionary algorithmic modelling, symbolic logic modelling, artificial intelligence modelling, and object-oriented computer modelling, in a logically structured approach to determining the integrity of engineering design. . | Theoretical Overview of Availability and Maintainability in Engineering Design 393 off-system repair and logistics capability to maintain the engineered installation. However because of the peculiar nature of these parameters none are considered in this research although it is essential to have a complete set of on-system and off-system indices to adequately assess system maintainability and the total maintenance burden. b Diagnostic Systems and Built-In Testing One aspect of maintainability that has received significant attention in recent system designs is the use of automatic diagnostic systems. These systems include both internal or integrated diagnostic systems referred to as built-in-test BIT or built-in-test-equipment BITE and external diagnostic systems referred to as automatic test equipment ATE or offline test equipment. The following concepts focus on BIT but apply equally to other diagnostic systems. Need for automatic diagnostic systems BIT As technology advances continue to increase the capability and complexity of modern engineering processes particularly in space and military systems more reliance is being placed on the use of automatic diagnostics as a means of attaining the required level of failure detection capability. The need for BIT is driven by operational availability requirements which cannot allow for lengthy MTTRs associated with detecting and isolating failure modes in engineering designs especially in microcircuit technology equipment. Because BIT is applied within a system s function and at the same functioning speed it affords the capability to detect and isolate failures that conventional test equipment and techniques cannot provide. A well-designed BIT system can substantially reduce the need for trained field-level maintenance personnel by permitting less skilled personnel to locate failures and channel suspect equipment to centralised workshop repair facilities that are equipped to repair defective equipment. However BIT is .
