Design and Analysis of Tug-Enabled Engine-Off Taxiing Operation using Hierarchical Multi-Agent Planning

Abstract

Growth in air traffic demand and the increasing importance of reducing emissions cause airports to consider the improvement of their ground surface movement operations in terms of efficiency and environmental impact. Over the past years, engine-off taxiing techniques have been considered to reduce the environmental impact of airport taxiing operations. One promising technique is Tug-Enabled Engine-Off Taxiing, a concept in which aircraft are towed to the runway by an external towing truck. However, implementation of this concept changes operations at the airport and creates challenges to coordinate and control vehicles efficiently and safely. Although operational changes are mostly expected in the bay areas and around decoupling locations close to the runways, especially bay areas are often excluded or simplified in existing research. In this work, we therefore aim to analyze Tug-Enabled Engine-Off Taxiing by using a detailed airport layout that includes bay area movements, such as push-back and engine start. A novel hierarchical multi-agent planning approach is used to route aircraft over the airport as an alternative to the current Air Traffic Control System. Vehicle movements are planned by a routing algorithm that accounts for shapes and kinematics. Real-world flight schedules from two days, under different runway modes of operation, were used to simulate ground surface movement operations. We compared outbound Tug-Enabled Taxiing to Multi-Engine Taxiing (MET) operations regarding taxi time, taxi distance, and bay area taxi times. Aircraft engine start times and tug decoupling durations were varied between in short, medium, and long scenarios. Our results show that the difference in taxi time between Tug-Enabled Taxiing and MET largely depends on the engine start time, decoupling duration, and taxiing distance to the runway. For runways far away from the ramps, lower taxiing velocities and the need for tug decoupling resulted in longer outbound taxi times in the Tug-Enabled Taxiing scenarios. However, in scenarios with long engine start time combined with short decoupling duration, the increase in taxi time was largely balanced out by a reduction of bay area taxi time. This trend becomes even more visible for operations to runways close to the ramps, since the engine start time forms a larger share of the total MET taxi time. Inbound flights were not significantly influenced by the Tug-Enabled Taxiing concept for outbound aircraft.