Component repairs: when to perform and what to do?

In this paper, a new indicator is proposed, that reflects the "state" of a major component in function of the ages of the (groups of) parts of which it consists. The contribution of the ages of the parts to the state of the component is defined by their weights. The indicator can be interpreted as the virtual age of the component, and can therefore be used to define age-reduction factors of different types of repair in a virtual age or age-reduction process. The state indicator is used as the time scale in a proportional intensity model. In this way, the joint impact of different repair strategies and covariates on the component failure intensity can be evaluated. This relationship is then used to address the question of which parts to replace whenever a component comes in for repair and when to set the preventive repair interval, in order to minimize the expected costs per unit time until the next repair. An example is given.