In the first paper we focused mainly on establishing a sequential method for the selection of a maintenance technique for mechanical systems. The selection problem is studied for the components having considerable consequences and a non-negligible failure intensity. Identification of these components based on their failure mechanisms and failure causes is discussed and a modified version of the usual Failure Modes, Effects and Criticality Analysis, FMECA is suggested. A cumulative sum chart is proposed to identify a replacement time. This is explained by way of two examples. In order to run cost per unit time is proposed. The selection of a maintenance technique based on the intrinsic information of monitoring parameters is introduced.

Ability of a monitoring parameter in predicting failures, can be described as a probability of failure in the future conditionally on the current value of a model monitoring parameter. Thus, the second paper is focused on introducing a model relating a condition dependent failure rate to a component condition. For the selection of a cost-effective technique a modified proportional hazards model, PHM, is proposed. The modified model is able to reveal the effect of observing monitoring parameters and operating conditions on failure rate function.

A graphical method, based on a Generalized Total Time on Test, a GTTT- plot, for the selection of a cost-effective technique is proposed in the third paper. Also, a graphical method to estimate the threshold level for a cost-effective technique based on the same concept is suggested. These methods are illustrated by way of an example.