Ground holding strategies for air traffic control under uncertainty

As air traffic congestion grows, ground-holding (or "gate-holding") of aircraft is becoming increasingly common. Ground-holding is the practice of delaying the departure of a flight due to anticipated congestion at the airport of destination, because it is both less expensive and safer, for aircraft to wait on the ground, prior to take-off, than in the air. The problem of developing strategies for deciding which aircraft to hold on the ground and for how long (the "ground-holding policy problem," GHPP) is a difficult one. The GHPP is: combinatorial, because of the large number of aircraft and landing periods ("slots"); stochastic, because there is often a large amount of uncertainty about the acceptance rates ("landing capacity") of the airports of destination; and dynamic, because the state of information regarding airport capacity and expected delays is updated throughout the day. Since ground-holding is only a relatively recent phenomenon, little has been done to date on developing sophisticated solutions to the GHPP which could potentially result in very large cost savings to the users of the XATC system. Research on probabilistic models of the GHPP has been limited to static solutions, producing "once and for all" ground-holds at the beginning of daily operations. The computational complexity of such models requires heuristic approaches in order to solve practical instances of the problem.