14The Schedule Adjustment Problem
Most major airlines publish multiple schedules throughout the year to respond to changes in demand levels associated with seasonality, competition, and changes in available resources (e.g. new aircraft, slots, gates, etc.). These schedules are usually published ahead of time (9–12 months) such that prospective travelers and travel agents can access these schedule and reserve seats on the scheduled flights. A common practice is to publish a schedule for every month in the year. Airlines develop these monthly schedules while maintaining their network structure and preserving adequate service frequency in the different city‐pairs to avoid losing loyal customers. Accordingly, most major airlines develop their schedules by tweaking and adjusting previous schedules to minimize schedule changes. This approach is known as the warm start approach (or incremental approach), in which an initial schedule(s) is adjusted in order to obtain the target schedule. There are several reasons for airlines to rely on the warm start approach (Lohatepanont and Barnhart 2004). First, building an entirely new schedule requires data that might not be available to the airline. Second, developing a new schedule from scratch is computationally intractable. Third, significant investment at airport stations will be needed if significant changes in network structure are introduced. Last, airlines prefer schedule consistency between seasons, especially in ...
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