Nested modeling of hazards in the national airspace system

Highly complex and coupled nature of the National Airspace System makes it challenging to understand the safety implications of changes to its operations.Acomprehensive assessment of the hazards associated with the introduction of new technologies must involve modeling of interactions among aircraft behavior, supporting infrastructure, and the operational procedures. The traditional approach to risk assessment does not focus on the relative timing of relevant events. The likelihoods of those events are computed externally, usually by means of physics-based simulations, which, while increasingly realistic in capturing physical phenomena, are limited to describing only few relevant interactions to keep the overall complexity tractable. This paper discusses an intermediate layer of analysis with enough fidelity to capture time-dependent coupling among relevant entities of the system that is compact enough to track a large number of those relevant entities simultaneously. To this end, Stochastic Petri nets are used to analyze the conflict resolution between the merging flows of air traffic for optimized-profile-descent approaches. Stochastic Petri nets are coupled with agent-based simulation, and the efficiency of the merging procedures and their sensitivity to wind conditions and the traffic patterns are analyzed. Finally, compact modeling of two off-nominal scenarios related to future procedures is discussed.