Operational feasibility of contrail avoidance by flight trajectory adaptation: first insights from the German 100-flights-trial

Over the past few decades, research has increasingly revealed the significant impact of non-CO2 emissions from aviation on global warming, with estimates suggesting they may account for as much or even more than the sector's entire CO2 footprint. While aviation produces various non-CO2 emissions, contrail cirrus is identified as one of the most significant contributor to aviation's climate impact. Whereas CO2 emissions linearly correlate to fuel consumption, this is not the case for contrail cirrus effects, making them more challenging to measure and mitigate. This highlights the importance of addressing contrail cirrus effects alongside CO2 and other emission reduction efforts in the aviation industry's pursuit of climate neutrality.

Here, we present first insights from the 100-flights-trial, a contrail avoidance demo trial by the German Aerospace Center (DLR) and the aviation industry tasked by the German federal government. In this trial, aircraft were actively rerouted (pre-tactical) to avoid airspaces with potential warming contrail cirrus formation. Existing models and tools were used to integrate the planning and execution of contrail avoidance flights into the flight operations processes. The analysis presented utilizes real flight data from 25 contrail avoidance flights operated by TUIfly which is then further analyzed using a modelling workflow consisting of DLR’s Trajectory Calculation Module (TCM), the Contrail Cirrus Prediction (CoCiP) model from the open-source pycontrails library, and ECMWF ERA5 reanalysis data. By comparing the originally planned trajectory, the contrail-optimized planned trajectory and the actual flown flight trajectory for each flight, we are able to quantify the effects of mitigation on parameters such as flight time, fuel consumption and the radiation effect of contrails. The methods developed may also be used to investigate the potential of the mitigation strategy and the impact on operational aspects like delay and fuel consumption. In addition, feasibility is considered with regard to airspace restrictions, optional direct routings, but also bad weather. We demonstrate through the implementation of contrail avoidance strategies that there is potential to achieve substantial reductions in the climate impact of contrails at a relatively low cost with comparable flight times. In addition, the choice of climate metric is shown to have little influence on the evaluation of the flights.