A different concept is used to schedule maintenance activities for components under CBM. Here, the degradation level is the criterion for defining the next maintenance activity. This means that it is not clear when the next maintenance activity will have to take place until a few days or weeks before the failure of a component. From a planning perspective, this policy can thus be positioned somewhere between the long-term (PM) and the short term (CM or reactive). As depicted in Table 1, we consider CBM as a policy for a mid-term planning horizon. CBM is thus of a more reactive nature than ABR, since it cannot be planned far in advance (Koochaki et al. 2011, 2012). It is expected that the reactive nature of the maintenance activities becomes even stronger if CBM is non-ideal. This may affect the possibilities for the grouping of maintenance activities