The Airline Exception Scheduling Problem

As part of its schedule planning task, a domestic airline must assign fleets (aircraft types) to legs (non-stop flight segments). Initially, for planning purposes, this fleet assignment is done for a daily, repetitive schedule, called a “skeleton” schedule, in which the same set of legs is assumed to fly daily. In practice, however, there are often significant changes in passenger demand patterns on weekends (and other days as well), warranting changes in scheduled legs and fleet assignments. Thus, the airline will include, in its actual schedule, certain variations or changes in the nominal “skeleton” schedule on particular days of the week. We refer to such changes as exceptions. A typical domestic airline may vary the fleet assignment of over 10% of its legs on the weekend alone. Thus, handling exceptions is an important airline scheduling function. We describe an approach, centered around formulating and solving a network flow problem, for efficiently scheduling such exceptions to the usual daily schedule. In addition, another procedure was developed to identify and suggest possible profitable exceptions. It implements graph theoretic methods to detect “cycles” of legs whose fleet assignment is unprofitable on a particular day. Some computational experience is discussed.