Aircraft maintenance cost consists of two elements. The first one is direct maintenance cost and the other one is indirect maintenance cost. The first element includes the costs that are directly related to the maintenance activities such as labor, material, tool and equipment. The second element includes the cost that does not directly affect operator's maintenance budget, which is defined as downtime cost. In most cases, downtime cost is neglected claiming that downtime is a natural fact of maintenance. However, to our surprise, as maintenance period gets longer and the required tools and materials get more complex, downtime starts to cost operator in the same way the maintenance activities do. Therefore, the aim of this study is to examine the elements of maintenance downtime and to what extent they affect the total maintenance cost.