EUROCONTROL-CANSO Sustainable Skies Conference: reducing contrails and their non-CO₂ effects on global warming through operational mitigation

MUAC's live contrail prevention trial and real-time simulations show that contrail formation and their harmful impact towards climate change can be avoided with relatively small vertical deviations from the flight plan. As long as air traffic is low also the impact of contrail prevention operations on capacity is low. However, capacity reductions in the range of 20% can already be expected in moderate traffic conditions for safety reasons.

The world’s first live contrail prevention trial carried out in 2021 by EUROCONTROL's Maastricht Upper Airspace Control Centre (MUAC) and the German Aerospace Centre DLR saw several airlines participate in the upper airspace of Belgium, Luxembourg, the Netherlands and North-West Germany. At the time, civil aviation was severely impacted by the pandemic. The low traffic demand during this period encouraged aviation and environmental specialists to go ahead. The results surpassed many expectations. Trial data and statistical analysis from the trial proved that contrails can be avoided and prevented thanks to relatively small vertical deviations from the flight plan of approximately 2,000 feet, thus reducing their impact on climate change and global warming. This, however, required further investigation, in particular the effects of contrail prevention operations on capacity.

Real-time simulations were conducted to assess the impact of contrail prevention measures on capacity. One of the objectives of these real-time simulations was to find out whether it was more appropriate for airlines to file climate-optimal flight plans pre-tactically or rather whether air traffic control should make tactical changes to flight levels based on real-time weather information.

MUAC conducted these real-time simulations with air traffic controllers, who were tasked with blocking certain flight levels for the sake of contrail prevention. The blocked flight levels modelled relatively realistic weather situations, and different simulated traffic demand levels were evaluated.

Discussions with the participating air traffic controllers revealed that the impact on airspace capacity is proportional to demand. In low traffic conditions (e.g. at night), the impact of contrail prevention operations on capacity is low. However, for safety reasons, capacity reductions in the range of 20% can be expected in moderate traffic conditions without vertical airspace splits and with a few blocked levels. By contrast, normal or high traffic conditions increase the impact of contrail prevention operations exponentially.

The application of contrail prevention measures in the late afternoon – which is the time when warming contrails tend to be produced – will therefore require more research to cope with the expected capacity challenges.

One important outcome of the real-time simulations is the finding that if all airlines plan for contrail prevention, and if flights enter the airspace at the requested contrail-clear levels, the tasks of air traffic controllers in managing this additional complexity will be eased.

As a next step, MUAC aims to trial a combination of the pre-tactical and tactical models in a mixed operational mode, where airlines plan optimised flight plans and air traffic control adapts as needed with further local optimisation.

The 2023 real-time simulations in MUAC airspace have provided valuable results and will lay the foundation for the smooth and safe introduction of contrail prevention in ATC operations. In parallel, more studies will be carried out on the required legal framework and technical enablers, and the success of contrail prevention in mitigating climate change will continue to be monitored.