Scheduling personnel for the build-up of unit load devices at an air cargo terminal with limited space

This paper addresses the preparation of unit load devices (ULDs) at an air cargo terminal. This process is difficult to plan for many airlines, which face the challenge of assigning a limited number of workers to a limited number of workspaces available for preparing the ULDs, while respecting the requirements imposed by an existing flight schedule. During the preparation of ULDs, the objectives are to comply with the flight schedule, not to exceed the available space at the terminal, and to minimize the maximum workforce employed over time. To support airlines in realizing efficient ULD preparation processes, this paper proposes a mixed-integer linear programming model as well as a generalized set partitioning reformulation of this problem. Based on the latter formulation, we develop different heuristic strategies, some of which are shown to solve this NP-hard problem to near-optimality in a matter of merely 10 s, decisively outperforming a simple rule of thumb frequently used in practice. We also investigate the inherent trade-off between workforce and space utilization.