Aircraft base maintenance consists of hundreds of tasks including preventive, corrective and modification tasks which have to be scheduled to a few check moments per year. The allocation of tasks to checks represents a complex scheduling problem due to the constraints involved. A mixed integer linear programming model was developed to optimize the allocation of the complete base maintenance workload and maintenance checks over a four year period. The model optimizes for resource capacity and interval efficiency. CPLEX has been used as solver. An iterative solution technique loops around the model which yields an approximate optimal solution. The model was developed for a large MRO service provider. Its outcome provides the MRO with an integral insight into the complete workload distribution over a tactical planning horizon for all checks. This insight can help to optimize the allocation of maintenance tasks and resource capacity which will contribute to a higher fleet availability.