This is a full text of my presentation titled "Evaluation of Maintenability Improvement by Systems Reliability Growth" at the First Beijing International Conference on Reliability Maintenability and Safety (BICRMS'92). This thesis describes evaluation methods of reliability growth for field working systems by surveying maintenability improvement. And it also touch upon customer satisfaction. As unavailability is suitable for measuring reliability, I use in this thesis a decrease in unavailability per month as a means to evaluate reliability and its growth. "Maintenability" is broadly defined as a system's capability to maintain, repair and recover its functions with the aid of failsoft and RAISIS. The term "Customer satisfaction" is difficult to define, but on the practical market basis it can be fairly easily and objectively measured by examining the cancel rate by customers. This thesis includes topics such as: (1) When a system is in disorder it can restore its original functions although, strictly speaking, such system changes are classified as another systems statistically. (2) Despite this, we need to evaluate a specific system's reliability continously, and study reliability growth, industrial life, and customer satisfaction. Unavailability can be reduced by improving systems through upgrading component.

This paper deals with two optimal preventive maintenance policies, i.e., Policy I and Policy II proposed by R. Barlow and L. Hunter, and in particular emphasizes on the characteristics of the optimal maintenance theories due to numerical analysis. Through this paper, the Weibull model is adopted as a failure modes and its shape parameter β plays an important role. According to the results newly obtained, we discuss the characteristics of the two types of policies and their advantages and disadvantages. Next, the new results are applied to the field data of failure and maintenance in order to investigate the actural maintenance techniques.