Queue management techniques for avoiding gridlock in NAS-Wide simulations

Simulation models are useful for studying National Airspace System (NAS) operations. A common simulation technique involves modeling airspace resources such as sectors and airports using queues. Resource capacities are enforced by placing flights into a queue until sufficient capacity is available for advancement to the next resource. Under highly constrained conditions during which demand is at or near the resource capacity, stalemates can occur leading to gridlock and excessive queuing delays in these simulations. The techniques with which stalemates are resolved play an important role in simulation results. The purpose of this study was to evaluate various queue management techniques and in particular provide recommendations on how the sector entry logic might be enhanced in the existing System Wide Analysis Capability (SWAC) simulation model. For this purpose, a standalone Evaluation Platform was developed for testing full-scale NAS-wide scenarios. Results from studying both deterministic and stochastic sector entry logic along with four alternative stalemate resolution algorithms are presented in this paper.