Contrail, or not contrail, that is the question: the "feasibility" of climate-optimal routing

Abstract: The environmental impact of aviation has been a focus of significant research for several decades. While there is a broad consensus among stakeholders on reducing carbon emissions, leading to efforts to improve route efficiency in air traffic management, the impact of non-carbon emissions like contrails has sparked a different debate. Some organizations have already moved to pre-operational trials for contrail avoidance through flight re-routing, with recent industry projects fast-tracking these operational strategies. This paper addresses the practical challenges of implementing contrail-aware routing. Building on our previous research, which enables the generation of wind-optimal 4D trajectories using grid-like cost functions, we utilize the TOP tool and the OpenAP aircraft performance model to analyze the trade-offs between fuel consumption and contrail avoidance. We also examine the impact of weather forecast uncertainty on contrail mitigation, the effects on airspace capacity and network operations, and the implications for aviation regulatory frameworks. To investigate these challenges, we reconstructed a dataset from OpenSky data, encompassing all flight trajectories over Europe on a day with significant contrail potential. Our data-driven analysis highlights the potential difficulties in implementing contrail-optimal routing in practice, particularly concerning uncertainties in weather forecasts, impacts on airspace capacity, and questions of responsibility for optimal routing. Overall, we argue that contrail-optimal routing should be approached with caution, as its implementation may not be as straightforward as some stakeholders suggest.