Due to its speed and reliability, the air cargo industry is essential in supply chain logistics and is constantly growing. A cargo airline's aircraft must always be available to the company's network to be profitable. A lack of spare parts can cause aircraft to be grounded whenever an aircraft part fails, which makes spare parts management vital for the airline's success. To contribute to this essential task, we present a mixed integer program to optimally distribute spare parts at the outstations of a German air transport company. The objective function is a cost-based minimization of aircraft on ground situations where aircraft cannot deploy as planned and the schedule disrupts. The model is based on six-monthly flight schedules and previous spare part demand information. We compare the results with the company's spare part consumption in the second quarter of 2022. In addition, we include scenario analysis for outstation and home base parameters and limitations of the spare parts purchase quantity. We show that the generated solutions support logistic planners and can be used to reveal problems such as lack of spare parts and insufficient storage space.