✈️ Can airlines avoid contrails? American Airlines just ran one of the biggest tests yet.
Despite a high reduction in contrail warming for the avoidance flights flown, there is still work to do to have dispatchers fully embrace contrail avoidance
A new study released this week describes one of the largest real-world tests of contrail avoidance conducted, and the results offer one of the clearest signals yet that airlines can reduce contrail warming using existing flight-planning tools and workflows.
The trial involved American Airlines, one of the world’s largest airlines by passengers and fleet size. Over a 17-week period in early 2025, researchers and technology providers worked with the airline to test contrail-aware flight planning on more than 2,400 transatlantic flights. About half of these flights were randomly assigned to test contrail-aware planning, while the others served as a control group.
Using flight planning software from Flightkeys with integrated contrail avoidance, dispatchers planning overnight flights from the United States to Europe could see a contrail-optimized flight plan designed to avoid atmospheric regions where contrails are likely to form. They could then decide whether to release that flight plan to the crew.
To measure the impact, the study used satellite observations to detect contrails and attribute them to individual flights, enabling researchers to assess whether observed contrail formation changed in the real world.
69% reduction in contrail warming
Across the full experiment, flights where contrail-aware planning was introduced produced 11.6% fewer observable contrails than the control group.
But the effect became much clearer when the optimized routes were actually flown. For flights that followed the contrail-optimized plan, observable contrail formation fell by about 62%, with an estimated 69% reduction in contrail warming.
Just as important, the trial found no statistically significant increase in fuel use.
A large trial, but still a small fraction of avoidance flights flown
Despite the experiment’s scale, the number of flights that actually flew contrail-optimized routes was relatively small: Out of more than 1,200 flights eligible for contrail avoidance, dispatchers released contrail-optimized flight plans for about 15% of them, and only 112 flights ultimately flew the optimized plan.
Participation in the trial was voluntary, meaning dispatchers could simply proceed with a standard flight plan if operational priorities required it. In interviews conducted after the trial, dispatchers cited several operational reasons for not using the contrail plans more often, including workload, turbulence and weather considerations, preference to stay within the North Atlantic organized track system, and limitations in the flight-planning interface.
Measuring only the contrails we can see
Another important caveat is that the study measured observable contrails detected in satellite imagery. Not all contrails are visible to geostationary satellites, meaning the total climate impact reduction may differ from the reduction in observable contrail length.
However, larger and more persistent contrails — which may account for a disproportionate share of warming — are also more likely to be detected by satellites. The researchers therefore believe the results capture a significant portion of the contrails most relevant to climate warming.
How quickly can we scale contrail avoidance
In 2023, American Airlines worked with the same group of researchers from Contrails.org, Imperial College London, and Google Research to conduct its first small trial. One future focus area could be to enhance dispatchers’ confidence in choosing the contrail-optimized flight plan to get a much higher adoption rate than in this trial.
As we wrote about last month, a new study shows that the biggest contrail climate risk is to do nothing. And with one of the world’s largest airlines actively testing contrail avoidance at scale, the question is becoming less whether the approach can work, and more how quickly it can be scaled.
Contrail impact explained: The blanket effect and the mirror effect
As a communicator, I am always on the lookout for explanations that feel logical, easy to remember, and simple to communicate. This is why I want to highlight this LinkedIn post by Gular Ismayilova, Co-founder of Nexus Lab, a contrail-avoidance tech provider, which distinguishes between warming blanket-effect contrails and cooling mirror-effect contrails. Great way of wording it.
To all the new Blue Lines followers: Welcome.
In 2025, we added 33% more subscribers. It is always a pleasure to have more people interested in the progress of contrail avoidance – the most promising solution to lower aviation’s climate impact and potentially one of the fastest ways to reduce global warming overall.
Go to Blue Lines’ website to explore contrails in depth.
See you soon.
Joachim Majholm,
Blue Lines