Contrail Avoidance 101

What is Contrail Avoidance, Who is doing it, and Why?

Jan 23, 2025

“Aviation is a hard to decarbonize industry,” according to everyone in the industry. As such, the aviation sector has to find innovative and unique ways to curb its climate impact while still meeting growth targets. With its ambitious objective to achieve net-zero carbon emissions by 2050, the aviation industry is already working to mitigate both CO2 and non-CO2 emissions wherever it can. Whether through the development and deployment of SAF, the improvement of aircraft manufacturing, or the enhancement of air traffic efficiency, steps are being taken to address the climate stressors of aviation.

Of the many tools in aviation’s decarbonization toolbelt, one is gaining recognition and credibility as a cost-effective and ready-to-implement solution: contrail avoidance. Contrails are the single biggest component of aviation’s non-CO2 contribution to climate change, therefore, finding ways to mitigate and even avoid their creation would be a big step toward reducing the non-CO2 impacts of aviation. If you are curious about contrail avoidance and want to know what it is, who is working on it, and decide why it matters, then read on.

What is Contrail Avoidance?

Navigational contrail avoidance is the act of adjusting the flight path of a given flight to avoid the ice supersaturated regions (ISSRs) in which persistent contrails are most likely to form. Research has shown that only 2% of flights are responsible for 80% of the energy forcing (EF) of contrails – these flights are known as ‘big hits.’ The same study found that small diversions around contrail-forming regions can greatly reduce the incidence of contrail formation, as well as the EF on the climate with minimal extra fuel burn. This avoidance is achieved once an ISSR is forecasted in the scheduled flight path and the aircraft is rerouted to fly either higher or lower to avoid the region and ultimately avoid creating a contrail.

What are ISSRs? Ice SuperSaturated Regions exist in the upper troposphere and lower stratosphere where the temperature is particularly cold – less than -42 degrees Fahrenheit – and the air is particularly humid – more than 100% relative humidity.

There are currently two prevailing strategies for contrail avoidance – pre-tactical and tactical – and both of which require the support and approval of Air Navigation Service Providers (ANSPs). ANSPs manage the aircraft in-flight and are responsible for the safe and efficient passage of flights. They are critical in contrail avoidance because they 1) approve pre-tactical flight plans which are arranged in advance of the flights and 2) authorize tactical rerouting of aircraft during flight. Both strategies are essential to the effective implementation of contrail avoidance, especially with the challenges of forecasting and tracking exactly where ISSRs will be.

Flight Diversion Model | Teoh et. al. 2020

Though the aviation sector has become adept at predicting and avoiding storms and areas of turbulence, there are still limitations to predicting contrail-forming regions with consistent accuracy. This is one of the main barriers to the immediate application of contrail avoidance strategies. Without the certainty of knowing where these regions are, where they may move, and how long they will last, flights may be rerouted unnecessarily. These unnecessary diversions could lead to flights creating contrails that were not going to be created or avoiding regions where contrails were not going to form, causing added fuel burn for no benefit.

The potential for added fuel burn from rerouting flights is another quandary under consideration. Theoretically, any diversions to the flight path would use more fuel and release more CO2 into the atmosphere, adding to the overall flight costs both financially and to the climate. However, study after study show the feasibility of contrail avoidance with benefits that outweigh the operational risks as additional costs, fuel burn, and CO2 trade-offs are minimal when compared to the reduction in climate forcing by avoiding the creation of contrails.

Comparison of CO2 Emissions and Contrail Warming with Contrail Avoidance | Transport & Environment

Furthermore, SAF will have a part to play as well. With its lower aromatic content and fewer soot particles, SAF can reduce the likelihood of contrail formation. Though supply is currently limited, there is research probing the idea of targeting the use of SAF to flights most likely to create warming contrails, subsequently reducing the EF of big hit trips. Even deploying SAF blends to night flights known to be more warming is a plausible strategy for contrail mitigation. Though promising, these notions need further trials and organizations willing to develop the technology and to measure the results of those trials.

Who Is Researching Contrail Avoidance?

Delving into the intricacies of contrail avoidance can be an onerous task. With the weight of the uncertainties impeding rapid progress, trialing and understanding the effectiveness of avoiding contrails has been a test of patience. Yet, there are organizations and teams working hard to elucidate the costs and benefits of real-time application. For example, in 2023 American Airlines and Google partnered to test Google’s AI-based contrail prediction model, monitoring 70 flights over six months. These tests proved the efficacy of slight deviations, as pilots were able to reduce contrail formation by 54% with an estimated 2% of additional fuel burn.

Breakthrough Energy also came alongside Google and American Airlines providing their highly sophisticated software to forecast contrail-forming regions. The tests relied on their prediction tool, pycontrails, to cross-reference Google’s AI predictions to ensure optimal accuracy for contrail avoidance.

Google’s AI-Based Contrail Detection Map | Google

There are other companies also harnessing technology to improve contrail prediction and data analysis to optimize flight routes for contrail mitigation. The innovative efforts of these groups have greatly improved the understanding of contrail prediction and what is required to avoid them.

For example, Estuaire is revolutionizing the measurement of life-cycle emissions for flights to improve flight efficiency and develop trajectories which are least likely to form persistent contrails. Similarly, Nexus Lab has developed software which uses machine learning to analyze flight and meteorological data to predict contrail-forming regions and strategically route flights around those regions. Then there is Flightkeys, a flight-planning service provider utilizing their 5D flight management system to optimize and enhance in-flight trajectories for both contrail prediction and avoidance. Their flight simulations led to the afore-referenced study proving the operational viability of contrail avoidance. Finally (at least for this part of the list), contrail adversaries SATAVIA have optimized flight plans to prevent contrails with their DECISIONX weather prediction model. Their software has been tested by Etihad Airways and is being integrated into their flight routing operations.

While these organizations are driving the industry towards contrail mitigation and making the technology more accessible for airlines, airports, and ANSPs, various groups are producing progress reports of their own. The RMI Contrail Task Force is a consortium of airlines, manufacturers, researchers, flight planners, and NGOs, working toward reducing aviation’s climate impact. Their comprehensive report on contrail management offers a concise overview of all things contrails, digging into the details of what contrail management is, how it works, and what needs to be done to make it a reality.

In the same way, Transport & Environment , Europe’s lead advocates for clean transport and energy, have released their own comprehensive report which gives a full-scale breakdown of contrail avoidance. The report presents the facts around contrail avoidance, builds on research from across the industry, and makes the case for why contrail avoidance is the “opportunity of the decade.” They claim that by targeting the most warming flights – the big hits – contrail avoidance can be a no-regret solution to one of aviation’s main climate conundrums. A sentiment supported by this open letter from climate scientists and shared by the many companies working to bring contrail avoidance to the skies.