Condensation trails, or contrails for short, have been part of aviation since the inception of jet engines. Their impact on the environment is not negligible as they are forming high-altitude ice-cloud layers that trap outgoing heat in the atmosphere, creating a net warming effect similar in magnitude to CO2 emissions from airlines. French regional airline Amelia, which specialises in charter flights, wet leases, and medical evacuation flights, partnered with Thales to test a new version of the Flight Optin tool, which is traditionally used for fuel optimisation. The latest version also optimises for contrail avoidance by identifying and avoiding flight levels where weather forecasts indicate that contrails are most likely to form.
One year, 6,500 flights operated, 59 flights modified
Thales and Amelia presented the results of their fleet-wide contrails avoidance operations in 2025. All 6,500 flights operated by Amelia were examined to avoid contrails and 59 were assigned a different flight level to do so.
The optimisation takes place at the flight planning phase, rather than tactically during the flight. Contrail optimised flights are then operated according to their flight plans. Tactical flight level changes would create an additional workload for air traffic controllers and could cascade across multiple sectors and control centres. The Flight Optin approach avoids this by making decisions upfront, before the flight is conducted.
Significant CO2 equivalent savings, little extra fuel consumption
The impact of contrails is measured in CO2 equivalents (CO2e), allowing it to be compared directly with CO2 emissions. Adjusting the flight levels of just 59 flights resulted in savings of over 2,000 tonnes of CO2e, corresponding to an average reduction of around 70% per modified flight.
However, changing a flight’s cruising flight level has a direct impact on the fuel burn. Climbing higher requires more fuel, and flying at a lower level also leads to a higher fuel flow. Thales and Amelia took those impacts into account. The additional fuel amounted for less than 0.1%, a value which is negligible compared to the benefits.
How to scale from here?
The results achieved on Amelia’s operations clearly demonstrate the environmental benefits at airline level. Scaling this approach further raises important questions.
What happens if all airlines target the same handful of flight levels because they are the only ones forecasted to not generate contrails? Would network managers need to regulate access to those levels to avoid congestion, or distribute traffic more evenly across the airspace, at the price of generating contrails?
Another challenge is cultural. How to change the mindset of flight dispatchers from fuel optimisation and give them a wider view, including sustainability? How to incentivise airlines to put such tools in place, as the savings are in terms of saved CO2e, and not directly in terms of fuel used?
These questions go beyond the tool itself. They point to a broader evolution in aviation. The work carried out by Thales and Amelia is a first step, but it must continue as preventing contrails is one of the many ways aviation can reach its sustainability goals.
