This Master´s thesis covers the improvement of a life-cycle cost (LCC) model to predict the shop visit costs of Rolls-Royce BR725 aero engines. Based on estimates and previous engines maintenance data, this model utilises an internally developed tool (DMTrade) to predict the average time on wing from entry into service to the first shop visit and the respective costs. The first part of the analysis was based on the optimization of the model. Initially, DMTrade was modified in order to display the costs relative to the specific case of study, which was the first proactive engine life management (PELM) shop visit.