Optimal Slot Allocation for European Air Traffic Flow Management

Abstract

Responding to the increasing congestion of the European airspace, the Central Flow Management Unit (CFMU) of the European Organization for the Safety of Air Navigation (EUROCONTROL) started applying, on 28 April 1995, a centralized slot allocation process by means of a Computer Assisted Slot Allocation (CASA) procedure. Two basic objectives of slot allocation are to ensure the safety of crowded airspace and to minimize the total aircraft delay by optimizing the use of the available capacity. CASA, however, is a heuristic algorithm (based on the “First Planned, First Served” principle) rather than an optimization procedure. The present work continues and builds upon a series of recent attempts by various researchers to examine optimization models for slot allocation. The work consists of two somewhat disparate parts, a theoretical and a computational one. First, a new integer programming model of the European Slot Allocation Problem (SAP) is presented. The model is specifically adapted to the current needs of the CFMU, but some extensions that anticipate possible future needs of the CFMU are also presented. Second, based on a modification of a previous model from the literature, a computational comparison of optimal slot allocation with current slot allocation practice is effected. The computations were performed with real data provided by EUROCONTROL and indicate that, by applying optimal slot allocation, the total delays imposed by CASA can be reduced in some (but not all) cases by about a third, while the maximum delays imposed by CASA can sometimes also be reduced. The comparisons with CASA need to be qualified in several ways; nevertheless, given that the annual costs of delays are estimated to be of the order of billions of U.S. dollars, the computational results suggest that applying optimal slot allocation might result in significant savings.