An efficient airline re-fleeting model for the incremental modification ofplanned fleet assignments

Airlines typically manage their annual business cycle by subdividing the ye ar into a sequence of scheduling periods that span about a month each. Flee t assignment represents an important step in the planning process for each new scheduling period and is usually undertaken using computer-based optimi zation models. Once an, initial fleet assignment solution is achieved and b efore "freezing" the assignments, planners spend significant effort in, ana lyzing, modifying, and committing the individual components of the solution throughout the flight network. This manual step results in local modificat ions to the initial solution, and is necessary to reflect business judgment calls that cannot be captured by the optimization model. In addition, plan ners find it imperative to modify the initial fleet assignment solution, to react to inevitable changes to the planning environment related to the pla nned schedule, demand forecast, number of available aircraft, crew staffing levels, and a host of other scheduling constraints. The above-described pr ocess of incrementally fine-tuning and modifying the initial fleet assignme nt solution is referred to as re-fleeting. It is characterized by (1) the r equirement of quick solution time to allow frequent re-fleeting exercises, (2) the meed for multiple alternative high-quality solutions to choose from , and (3) the constraint that the new solution differs from the prior one i n a controlled and limited fashion. We demonstrate in this paper that globa l fleet assignment model formulations can be used to address the re-fleetin g problem in an effective fashion.