Fleet routing and flight scheduling are important in airline operations. In particular, they always affect the usage efficiency of facilities, the establishment of timetables and crew scheduling. As a result, they are essential to carriers' profitability, level of service and competitive capability in the market. This research attempts to develop an integrated model and a solution algorithm to help carriers simultaneously solve better fleet routes and proper timetables. In order to manage the interrelationships between trip demand and flight supply, we apply a time-space network model to formulate the movements of aircraft and passenger flows. Mathematically, the model is formulated as a special multiple commodity network flow problem. On the basis of Lagrangian relaxation, the subgradient method, the network simplex method, the shortest path algorithm, the flow decomposition algorithm and the least cost flow augmentation algorithm, we develop a Lagrangian-based algorithm to efficiently solve the problem. The results of a case study have shown the model to be useful for airlines to improve their operations.