Balancing throughput and safety: An autonomous approach and landing system (AALS)

One of the bottlenecks in air traffic flow is the final approach segment and the runway. Flights must be sequenced and spaced before the Final Approach Fix (FAF) to meet the safety separation requirements on the final approach segment. The final approach segment is conducted in a highly stochastic environment due to factors such as atmospheric conditions, aircraft performance, fleet mix, and flight crew technique. The stochasticity is evident in the inter-arrival time distribution at the runway threshold. The magnitude of the left-tail of this distribution determines the Actual Level of Safety (ALS) of the process. When spacing methods such as Required Time of Arrivals (RTA) and self-separation are applied to the approach to eliminate gaps in the traffic flow, they result in a shift of the inter-arrival distribution to the left, and an increase in the magnitude of the left-tail resulting in a degradation in the ALS. A proposed Autonomous Approach & Landing Spacing (AALS) System is designed to continuously balance the throughput gains of RTA and self-separation with the safety for the approach and landing process. The AALS monitors the stochasticity of the approach process (via the runway threshold inter-arrival time distribution), and adjusts the spacing buffer-time to ensure the Target Level of Safety (TLS) is maintained even as the stochasticity in the approach changes. This paper describes the analysis of runway throughput and safety in the presence of stochastic approach performance with the AALS. The implications and limitations of this technology are discussed.