Safety Performance of Airborne Separation: Preliminary Baseline Testing

Consiglio, Maria; Hoadley, Sherwood; Wing, David; Baxley, Brian · 2007 · OpenAlex-citations

DOI: 10.2514/6.2007-7739

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Summary

This paper presents preliminary baseline results from the Safety Performance of Airborne Separation (SPAS) study, a NASA-led initiative designed to quantify the safety of distributed airborne separation systems under high-traffic conditions. Motivated by the need to evaluate the Next Generation Air Transportation System (NextGen) concepts, specifically Airborne Separation Assistance Systems (ASAS), the research aims to determine if aircraft can safely manage their own separation using advanced automation. The study focuses on a challenging baseline scenario involving randomized routes in generic, high-density airspace where all aircraft are constrained to a single flight level, simulating traffic densities up to five times current National Airspace System (NAS) levels. The experimental design utilized a distributed batch simulation platform called Airspace & Traffic Operations Simulation (ATOS) at NASA Langley Research Center. The system employed the Autonomous Operations Planner (AOP), a research model of ASAS automation, integrated into medium-fidelity aircraft simulators (ASTOR). A computer-based pilot model executed conflict management actions, including conflict detection and strategic lateral resolution, without human intervention. The simulation tested six sets of traffic densities, ranging from approximately 3.45 to 17.18 aircraft per 10,000 square nautical miles. Each run lasted six hours, with multiple replicates to ensure statistical robustness. The scenario generated random trajectories with high conflict rates and varied encounter angles to stress-test the system’s ability to detect and resolve conflicts within a 5-nautical mile separation standard. The results indicate that airborne separation was successfully performed across all tested densities, with the system resolving nearly all predicted conflicts. Specifically, out of thousands of conflicts, only three borderline cases resulted in a loss of separation, with maximum penetrations of less than 85 feet. These minor failures were attributed to modeling limitations regarding curved turns and the absence of prediction buffers in the baseline configuration. As traffic density increased, the frequency of conflicts per flight hour rose from 0.82 to 3.15. The analysis of actual closest points of approach (CPA) showed that while most aircraft maintained separations well above the 5 NM minimum, higher densities constrained aircraft to fly closer to the separation minima. Additionally, median conflict alert durations increased with traffic density, reflecting the greater complexity of finding resolution trajectories in saturated airspace. The significance of these findings lies in providing initial evidence that distributed airborne separation can maintain safety even at traffic densities significantly higher than current NAS operations. The study establishes a baseline for future research, which will incorporate three-dimensional airspace, realistic traffic patterns, and various error sources such as wind prediction errors and surveillance interference. By demonstrating that the AOP automation can handle high-conflict scenarios with minimal safety breaches, the paper supports the feasibility of ASAS applications for NextGen, offering critical data for subsequent safety analyses and comparisons with ground-based separation methods.

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