ABSTRACT
MAINTAINABILITY AND TESTING TECHNIQUES A significant proportion of maintenance procedures involve some form of diagnosis, not only to isolate the failed component but also to ensure that the repair operation is successful. Generally speaking, diagnosis can be either retrospective or predictive (see the discussion in Maxion and Siewiorek, 1985). Retrospective diagnosis seeks to determine what caused a system failure-the "What happened?" question. It can increase system availability by facilitating the quick revival of fallen systems. Predictive diagnosis seeks to determine when a failure will occur-the "What if?" question. Predictive diagnosis (failure prediction) can turn corrective maintenance into preven tive maintenance, thereby increasing perceived system reliability. Retrospective diag nosis enables operators and maintainers to assess problems immediately and restore service quickly, while predictive diagnosis can be used to guide preventive and preemptive maintenance. In each case, system downtime is reduced.
