Potential Impact of Operational Towing on Aircraft Emissions

Abstract

In this paper, the emissions mitigation potential of implementing operational towing at major European airports is evaluated. Using mixed-integer linear programming, a scenario simulating mixed taxiing operations is used to find the relationship between fixed vehicle costs and target emission savings at an airport and European level. Using formulae derived from the ICAO Advanced Emissions Model, fuel burn and emissions are calculated for conventional taxiing, single-engine taxiing (SET), and hybrid and electric operational towing. An assignment optimization model is used to assign vehicles in a vehicle fleet to flights; yielding the minimum fuel to cover a flight schedule with mixed taxiing operations. As the number of vehicles in the fleet increases, the saving potential for each additional vehicle is calculated, linking fuel and emission savings with vehicle costs. Two scenarios are compared; Scenario 1 with hybrid towing vehicles and Scenario 2 with electric towing vehicles. Applying this method to 30 case-study airports, a maximum jet fuel reduction of 66% for hybrid towing and 57% for electric towing is calculated; outperforming SET at 29 of the 30 airports. The average taxi time and aircraft compatibility are the driving factors that influence the maximum fuel savings potential. The total average taxi minutes of compatible flights is thus the best metric to predict an airport's potential, with a coefficient of determination equal to 0.96 for hybrid towing and 0.97 for electric towing. Because of the shorter refuelling downtime, hybrid vehicles can service more jobs per day than electric vehicles. This means a smaller hybrid fleet size can achieve the same CO2 and jet fuel savings on a European level. As the fleet size increases, the marginal savings per hybrid vehicle decrease at a higher rate than electric vehicles. This means that the maximum emissions savings potential can be a misleading metric for comparing strategies. By using this approach to link vehicle fleet size and potential savings, a more extensive trade-off of emission mitigation strategies is possible, allowing stakeholders to find the best strategy to fit a budget or emission savings target.