DLR and TUI fly collaborate to study aviation contrail climate impact

Investigating Aviation’s Climate Footprint: The DLR and TUI fly Collaboration

In a significant step towards understanding and mitigating the environmental impact of air travel, the German Aerospace Center (DLR) has initiated a pioneering flight campaign in partnership with TUI fly. For the first time in several years, a dedicated research aircraft is trailing scheduled passenger flights to capture real-time data on emissions. This initiative is part of the broader European research project A4CLIMATE, which aims to shed light on the complex relationship between modern engine technology and the formation of condensation trails, commonly known as contrails.

While the aviation industry has long focused on reducing carbon dioxide (CO₂) emissions, scientific consensus increasingly points to non-CO₂ effects as a major contributor to global warming. Specifically, contrails and the resulting cirrus clouds are believed to trap heat in the Earth’s atmosphere. We observe that this collaboration represents a critical shift from theoretical modeling to real-world validation, as researchers seek to determine how modern “lean-burn” engines influence the atmosphere compared to older technologies.

The campaign involves high-precision coordination between scientific pilots and commercial flight crews. By analyzing the exhaust plumes of aircraft in regular service, the project partners aim to develop robust strategies for climate-optimized flight planning. This effort highlights a growing industry trend where operational expertise and atmospheric science converge to address the urgent challenges of Climate change.

The Mission Profile: Chasing Data at 30,000 Feet

The core of this campaign features a DLR Dassault Falcon 20E research aircraft following a TUI fly Boeing 737 MAX 8. The operation requires the research plane to maintain a distance of approximately 10 kilometers (five nautical miles) behind the passenger jet. This specific distance allows the exhaust plume to evolve sufficiently for meaningful measurement while remaining fresh enough to analyze the immediate chemical and physical properties of the emissions.

The flights are currently being conducted on regular routes between Germany and Egypt. These corridors were selected due to their high probability of contrail formation, providing researchers with ample opportunities to gather relevant data. The focus of the study is the Boeing 737 MAX 8, which is equipped with modern CFM International LEAP-1B engines. These engines are characterized by their “lean-burn” combustion technology, which is designed to be more fuel-efficient and emit significantly less soot than previous engine generations.

Instruments onboard the Falcon 20E are tasked with measuring the evolution of soot and volatile particles within the exhaust plume for periods of up to 30 minutes. The primary scientific question driving this specific phase of the research is whether the reduction in soot emissions from these modern engines translates directly to a reduction in persistent contrails. While it is known that soot particles act as nuclei for ice crystals, the exact correlation between reduced soot mass and the number of ice crystals formed remains a complex variable that requires empirical verification.

“We want to understand how much global warming can be reduced when aircraft are more modern and smarter. It is still unclear whether less soot automatically means fewer contrails.”, Christiane Voigt, Project Manager at DLR Institute of Atmospheric Physics.

The Science of Contrails and Climate Impact

To understand the significance of this study, we must look at the mechanics of contrail formation. Contrails are created when hot, humid exhaust gases from aircraft engines mix with the cold air of the upper atmosphere. If the air is sufficiently cold and humid (ice-supersaturated), the water vapor condenses and freezes around particles, primarily soot, emitted by the engines. These ice crystals can persist and spread, forming cirrus clouds that prevent heat from escaping the Earth, a phenomenon known as radiative forcing.

Current scientific estimates suggest that these non-CO₂ effects could be responsible for a substantial portion of aviation’s total climate impact. Some studies indicate that contrails and contrail-induced cirrus clouds might account for up to two-thirds of the sector’s contribution to global warming, or approximately 1% to 2% of total global warming. Unlike CO₂, which remains in the atmosphere for centuries, contrails have a lifespan measured in hours. This presents a unique opportunity: if contrail formation can be prevented, the climate benefit is immediate.

However, the interaction between engine technology and atmospheric physics is not straightforward. While modern engines emit fewer soot particles, the particles that are emitted may still be sufficient to trigger contrail formation under certain conditions. Furthermore, the size and optical properties of the ice crystals formed by lean-burn engines may differ from those formed by older engines, potentially altering their warming effect. The data collected by the Falcon 20E is essential for refining climate models and verifying the accuracy of prediction tools used for flight planning.

The A4CLIMATE Project: A European Initiative

This flight campaign is a central component of the A4CLIMATE project, a major research initiative funded by the European Union. The project brings together a consortium of 17 partners from nine countries, including leading research institutions like the Max Planck Society, ETH Zurich, and Imperial College London, as well as industry heavyweights such as Airbus, Rolls-Royce, and Lufthansa Systems. The goal is to develop practical, science-based solutions to minimize the climate impact of aviation beyond simple fuel efficiency.

The A4CLIMATE strategy explores three primary avenues for mitigation. First, as demonstrated by the current TUI fly campaign, is the assessment of advanced engine technologies and their combustion characteristics. Second, the project is investigating the potential of SAF, which naturally contain fewer aromatics and therefore produce less soot, potentially reducing contrail formation further. Third, the project focuses on climate-optimized routing, or “contrail avoidance.”

Climate-optimized routing involves adjusting flight paths, often by small changes in altitude, to avoid regions of the atmosphere that are supersaturated with ice. If aircraft can fly around or above these “cold and humid” pockets, contrails can be avoided entirely. TUI fly has already been active in this area; since early 2025, the Airlines has routed several hundred flights specifically to avoid long-lasting contrails, providing operational data to researchers. The current measurement campaign serves to validate the predictions that guide these routing decisions.

“As a partner to science, we are providing our flights and our operational expertise. We want to help ensure that research results are quickly incorporated into everyday aviation practice, in order to reduce the climate impact of our flights.”, Christoph Todt, Head of Environmental Sustainability at TUI Airline.

Conclusion and Future Implications

The collaboration between DLR and TUI fly under the A4CLIMATE project marks a pivotal moment in aviation Sustainability research. By directly measuring the emissions of modern aircraft in real-world conditions, the industry is moving closer to understanding the full scope of its environmental footprint. The data gathered from these flights will be instrumental in calibrating the next generation of climate models and validating the effectiveness of new engine technologies.

Looking ahead, the implications of this research extend into regulatory and operational domains. As the European Union moves toward monitoring and reporting non-CO₂ effects, accurate data becomes a prerequisite for compliance. Furthermore, if the hypothesis regarding flight path optimization is validated, we may see a fundamental shift in air traffic management, where climate impact is weighed alongside safety and efficiency in flight planning. This offers a potential “quick win” for the climate, allowing the aviation sector to reduce its warming impact significantly even before zero-emission propulsion technologies become widely available.

FAQ

What is the main goal of the DLR and TUI fly collaboration?
The primary goal is to investigate the climate impact of contrails generated by modern “lean-burn” aircraft engines and to validate flight path optimization strategies that could reduce aviation’s global warming footprint.

How is the data being collected?
A DLR Falcon 20E research aircraft follows TUI fly passenger flights (Boeing 737 MAX 8) at a distance of approximately 10 kilometers to measure the composition and evolution of the exhaust plume in real-time.

Why are contrails considered a climate problem?
Contrails can form cirrus clouds that trap heat in the Earth’s atmosphere. Scientific estimates suggest they may contribute as much or more to global warming than the CO₂ emissions from aviation.

What is the A4CLIMATE project?
A4CLIMATE is an EU-funded research initiative involving 17 partners from 9 countries. It aims to develop solutions to minimize aviation’s climate impact through advanced engines, sustainable fuels, and climate-optimized flight routing.

Sources: TUI Group