Economic gain (EG), which is also called positive economic dependency (Nicolai and Dekker 2008), is one of the main motivations for companies to perform group maintenance activities. This gain occurs due to the economies of scale of performing collective maintenance activities. In our model, the economic gain is determined by means of equation (1). Here, N is the number of group maintenance activities, CPM is the PM cost and 0.1 represents the positive economic dependency between components. The EG is thus a fixed cost reduction (here 10% of the costs
associated with a single PM activity) for each group maintenance activity. Note again that the MTTR remains 24 hours.