Michel Bierlaire, Prem Kumar
We consider the assignment of gates to arriving and departing flights at a large hub airport. It is considered to be a highly complex problem even in planning stage when all flight arrivals and departures are assumed to be known precisely in advance. There are various considerations that are involved while assigning gates to incoming and outgoing flights (such a flight pair for the same aircraft is called a turn) at an airport. Different gates have restrictions, such as adjacency, last-in-first-out gates and towing requirements, which are known from the structure and layout of the airport. When optimizing the gate assignment costs, we consider different, and often, conflicting objectives such as maximization of gate rest time between two turns, minimization of the cost of towing an aircraft with a long layover, minimization of overall costs that includes penalization for not assigning preferred gates to certain turns, among others. One of the major contributions of this paper is to mathematically model all these features that are observed in the real-life. Further we also attempt to study the problem in both planning and operations mode, which has rarely been accomplished in the literature. For planning, we sequentially introduce different objectives to our gate assignment problem such as maximization of connection revenues, minimization of zone usage at airport and maximization of schedule reliability and include them to the model along with the relevant constraints. For operations, the main consideration is recovery of schedule by minimizing schedule variations and maintaining feasibility in the event of major disruptions. Additionally the operations models must have very, very short run times, in the order of a few seconds. These models are then applied to a real airline at one of its most congested hubs. Implementation is done using OPL and computational results for actual data sets are reported. For the planning mode, analyst perception of weights for the different objectives in the multi-objective model is used wherever actual dollar value of the objective coefficient is not available. The results are also reported for large, reasonable changes in objective function coefficients. For the operations mode, flight delays are simulated and the performance of the model studied. The final results indicate that it is possible to solve even large instances of real-life problems to optimality within short run times with conventional continuous time assignment model.