Airline fleet assignment with time windows

Recognizing that allowing variability in scheduled flight departure times c an result in improved flight connection opportunities and a more cost effec tive fleet assignment, we present a generalized fleet assignment model for simultaneously assigning aircraft types to flights and scheduling flight de partures. Our model, a simple variant of basic fleet assignment models, ass igns a time window to each flight and then, discretizes each window, allowi ng flight departure times to be optimized. Because problem size can become formidable, much larger than basic fleet assignment models, we develop two algorithmic approaches for solving the model. Our direct solution approach is good for speed and simplicity, whereas our iterative technique minimizes memory usage. Using data from a major U.S. airline, toe show that our mode l can solve real, barge-scale problems, and we evaluate the effects of sche dule flexibility. In every test scenario, the model produces a fleet assign ment with significantly lower costs than, the basic model, and, in a separa te analysis, the model is used to tighten, the schedule, potentially saving aircraft.