*2.1. Methodological Approach*

An empirical study was applied in this study to explore how a strategic sustainability perspective could be integrated into the maintenance strategy of transformers in order to approach relevant cost-effective sustainable maintenance. According to [35], an empirical study design should include five elements. The first element is the formulation of relevant questions related to the problem, which can be used in the first interview with the organization team. The second element is study propositions to be examined in the research. The third element is the identification of the problem to be studied. In this step, the problem should be defined and bounded. These three elements can help in identifying the data to be collected. The fourth element is linking the collected data to the study propositions. The last is establishing criteria for interpreting the findings. The last two elements elucidate the suggested process after the data have been collected. These elements are handled in this empirical study by using the ABCD procedure structure to assess sustainability. Therefore, the ABCD procedure acts both as a structure for achieving the study design and as a theoretical framework to be tested for its applicability in the context of maintenance strategy development.
