Sustainable Aviation
DLR and TUI fly collaborate to study aviation contrail climate impact
DLR and TUI fly research how Boeing 737 MAX 8 emissions influence contrail formation to reduce aviation’s climate footprint.
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 (COâ‚‚) emissions, scientific consensus increasingly points to non-COâ‚‚ 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 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.
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-COâ‚‚ 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 COâ‚‚, 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.
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.
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-COâ‚‚ 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.
What is the main goal of the DLR and TUI fly collaboration? How is the data being collected? Why are contrails considered a climate problem? What is the A4CLIMATE project? Sources: TUI Group
Investigating Aviation’s Climate Footprint: The DLR and TUI fly Collaboration
The Mission Profile: Chasing Data at 30,000 Feet
The Science of Contrails and Climate Impact
The A4CLIMATE Project: A European Initiative
Conclusion and Future Implications
FAQ
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.
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.
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 COâ‚‚ emissions from aviation.
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.
Photo Credit: TUI
Sustainable Aviation
Hawaiian and Alaska Airlines Partner for Hawaii SAF Production by 2026
Hawaiian and Alaska Airlines join Par Hawaii and Pono Energy to produce Sustainable Aviation Fuel locally with a $90M refinery upgrade, targeting 2026 deliveries.
This article is based on an official press release from Alaska Airlines and Hawaiian Airlines.
In a significant move toward energy independence and decarbonization, Hawaiian Airlines and Alaska Airlines have announced a strategic partnership with Par Hawaii and Pono Energy to establish the first local supply chain for Sustainable Aviation Fuel (SAF) in Hawaii. According to the joint announcement, the consortium aims to begin deliveries of locally produced SAF by early 2026.
The collaboration brings together the state’s largest energy provider, its primary air carriers, and local agricultural innovators. The project centers on upgrading Par Hawaii’s Kapolei refinery to process renewable feedstocks, specifically Camelina sativa, a cover crop that will be grown on fallow agricultural land across the islands. This “farm-to-flight” ecosystem is designed to reduce the aviation industry’s carbon footprint while diversifying Hawaii’s economy.
The airlines have committed to purchasing the SAF produced, providing the guaranteed demand necessary to make the project commercially viable. This agreement aligns with both carriers’ long-term goals of achieving net-zero carbon emissions by 2040.
Par Hawaii is spearheading the infrastructure development required to make local SAF a reality. According to project details summarized in the announcement and related reports, the company is investing approximately $90 million to upgrade its Kapolei refinery. This facility, the only refinery in the state, will convert a distillate hydrotreater to produce renewable fuels.
The upgraded unit will utilize HEFA (Hydroprocessed Esters and Fatty Acids) technology, a mature method for producing bio-jet fuel. Once operational, the facility is expected to have a significant output capacity.
In a joint statement, the partners emphasized the dual benefits of the initiative:
“This initiative will enable SAF production for more sustainable future flying and deliver economic benefits through the creation of a new energy sector and fuel supply chain in Hawai‘i.”
, Joint Press Statement, Alaska Airlines & Hawaiian Airlines
A critical component of this partnership is the sourcing of sustainable feedstock. Pono Energy, a subsidiary of Pono Pacific, will lead the agricultural operations. The project relies on Camelina sativa, a fast-growing, drought-tolerant oilseed crop that matures in 60 to 75 days. According to Pono Pacific, Camelina is ideal for Hawaii because it can be grown as a cover crop between other food crop rotations. This ensures that fuel production does not displace local food production. The crop helps prevent soil erosion, requires minimal water, and produces a high-protein “seedcake” byproduct that can be used as FDA-approved animal feed for local ranchers.
Chris Bennett, VP of Sustainable Energy Solutions at Pono Pacific, highlighted the circular nature of the project:
“Camelina represents a rare opportunity for Hawai‘i to build a true circular-economy model around renewable fuels.”
, Chris Bennett, Pono Pacific
The project is projected to support approximately 300 high-value manufacturing jobs at the refinery, in addition to creating new agricultural jobs for farming and harvesting. By producing fuel locally, the partnership aims to reduce Hawaii’s extreme dependence on imported fossil fuels, enhancing the state’s energy security.
The Cost and Scale Challenge
While this partnership marks a pivotal step for Hawaii, significant hurdles remain regarding cost and scale. SAF is currently estimated to be two to three times more expensive than conventional jet fuel. Without substantial subsidies or “green premiums” paid by corporate customers or passengers, this price differential poses a challenge for airlines operating in a price-sensitive leisure market like Hawaii.
Furthermore, while the projected 61 million gallons of renewable fuel is a substantial figure, it represents only a fraction of the total jet fuel consumed by commercial aviation in Hawaii. To run the refinery at full capacity, the facility will likely need to supplement local Camelina oil with imported waste oils, such as used cooking oil, until local agricultural production scales up. The success of this initiative will likely depend on the continued support of federal incentives, such as the Inflation Reduction Act, and state-level renewable fuel tax credits.
When will the new SAF be available? What is SAF? Will this project affect local food supply? Who is funding the refinery upgrade?
Hawaii Aviation Leaders Unite for Local SAF Production
Investment and Infrastructure Upgrades
The Role of Pono Energy and Camelina Sativa
Sustainable Agriculture
Economic Impact
AirPro News Analysis
Frequently Asked Questions
The partners expect the first deliveries of locally produced SAF to begin in early 2026.
Sustainable Aviation Fuel (SAF) is a liquid fuel currently used in commercial aviation which reduces CO2 emissions by up to 80%. It is produced from renewable feedstocks rather than crude oil.
No. The feedstock, Camelina sativa, is grown as a cover crop on fallow land or between food crop rotations, meaning it does not compete with food production.
Par Hawaii is leading the capital investment, estimated at $90 million, to upgrade the Kapolei refinery.
Sources
Photo Credit: Alaska Airlines
Sustainable Aviation
KLM Supports National SAF Fund to Strengthen Dutch Economy
KLM endorses the Wennink report urging a national Sustainable Aviation Fuel fund and €151-187B investment by 2035 to support Dutch economic growth.
On December 12, 2025, KLM Royal Dutch Airlines officially endorsed the findings of the newly released advisory report, “The Route to Future Prosperity” (De weg naar toekomstige welvaart). Authored by former ASML CEO Peter Wennink, the report outlines a strategic roadmap for the Dutch economy, emphasizing the need for significant investment to maintain national competitiveness.
Central to KLM’s endorsement is the report’s recommendation for the Dutch government to establish a national SAF fund. The airline argues that such a financial mechanism is critical to bridging the price gap between fossil kerosene and renewable alternatives, thereby accelerating the aviation sector’s transition to Sustainability without compromising the Netherlands’ economic standing.
Commissioned to analyze the Dutch Investments climate, the Wennink report warns that the Netherlands risks economic stagnation if it does not increase its annual growth rate to between 1.5% and 2%. According to the findings, maintaining current social standards, including healthcare, defense, and the energy transition, requires a massive capital injection.
The report estimates that an additional €151 billion to €187 billion in investment is needed by 2035 to modernize the economy. It identifies specific high-productivity sectors as essential pillars for future prosperity, including Artificial Intelligence, biotechnology, and aviation.
KLM has aligned itself with these findings, noting that a thriving business climate relies heavily on international connectivity. In its statement, the airline emphasized that the connectivity provided by Schiphol Airport is vital for Dutch trade and for attracting international headquarters to the region.
A key pillar of the aviation Strategy proposed in the report is the creation of a government-backed fund dedicated to Sustainable Aviation Fuel. Currently, SAF is significantly more expensive than traditional fossil kerosene, often three to four times the price, and suffers from limited supply availability.
KLM posits that a national fund would act as a catalyst to solve these market inefficiencies. By subsidizing the cost difference, the fund would make SAF more affordable for Airlines, ensuring they remain competitive against non-EU carriers that may not face similar sustainability mandates. Furthermore, the fund is intended to de-risk long-term investments for energy companies, encouraging the construction of domestic refineries, such as the facilities planned in Delfzijl.
“Such a fund would enable the Netherlands to accelerate the production of alternative aviation fuels and make them more affordable, thereby accelerating the sector’s sustainability.”
— KLM Royal Dutch Airlines
KLM used the release of the Wennink report to argue against unilateral national taxes or flight restrictions, which have been subjects of recent political debate in the Netherlands. The airline warns that such measures could harm the Dutch economy by reducing connectivity and driving business elsewhere.
Instead, KLM advocates for incentivizing sustainability. The airline suggests that the government must take a more active role in the energy transition rather than relying solely on industry mandates. According to the press release, “Real progress can only be achieved if government and industry work together and if the government takes a more active role.”
The endorsement of the Wennink report represents a strategic pivot for KLM, moving the conversation from “flight shaming” to economic necessity. By aligning its sustainability goals with the broader “Draghi-style” warnings about European competitiveness, KLM is positioning aviation not just as a transport sector, but as a geopolitical asset essential for the Netherlands’ survival as a trading nation.
However, this call for government funding comes amidst a complex backdrop. In 2024, KLM faced legal scrutiny regarding “greenwashing” allegations, with courts ruling that some “Fly Responsibly” advertisements painted an overly optimistic picture of SAF’s immediate impact. The push for a national fund can be interpreted as a tacit admission that the industry cannot achieve its 2030 and 2050 climate targets through market forces alone; without state intervention to lower the cost of SAF, the “green” transition remains economically unfeasible for legacy carriers.
KLM Backs Wennink Report, Calls for National SAF Fund to Secure Dutch Economic Future
The Wennink Report: A Call for Investment
The Proposal for a National SAF Fund
Strategic Competitiveness vs. Taxation
AirPro News Analysis
Frequently Asked Questions
Sources
Photo Credit: KLM
Sustainable Aviation
Airbus and SAF Hélicoptères Launch Book and Claim Model for HEMS SAF
Airbus and SAF Hélicoptères partner to use Book and Claim for Sustainable Aviation Fuel credits in Catalonia’s remote emergency medical services.
On December 10, 2025, Airbus Helicopters and the French operator SAF Hélicoptères announced a strategic partnership designed to decarbonize emergency medical services (HEMS) in Catalonia, Spain. The initiative utilizes a “Book and Claim” mechanism to supply Sustainable Aviation Fuel (SAF) credits to operations that physically cannot access the fuel, marking a significant shift in how remote aviation sectors approach environmental compliance.
The project focuses on two Airbus H145 helicopters operated by SAF Hélicoptères for the Catalan Department of Health’s Emergency Medical Services. According to the announcement, this arrangement allows the operator to reduce its carbon footprint despite the logistical impossibility of delivering physical biofuels to small, decentralized hospital helipads.
Emergency medical missions present a unique challenge for decarbonization. Unlike commercial airlines that refuel at major hubs with established infrastructure, HEMS helicopters often operate from remote bases or hospital rooftops. Transporting small quantities of SAF to these scattered locations by truck would be inefficient and could generate more carbon emissions than the biofuel saves.
To solve this, Airbus and SAF Hélicoptères have adopted the “Book and Claim” model. Under this system, the operator purchases SAF “certificates” representing the environmental benefits of the fuel. The physical fuel is then pumped into the aviation system at a central location, such as a major airport, where it is consumed by other aircraft. SAF Hélicoptères then claims the carbon reduction for its specific HEMS missions in Catalonia.
Jean-Louis Camus, Co-director of SAF Hélicoptères, explained the contractual necessity of this arrangement in the company’s statement:
“In my contract, I state that I will pay the equivalent of a portion of my helicopters’ fuel usage in exchange for a certificate.”
Airbus Helicopters is acting as the market facilitator in this pilot program. According to the release, the manufacturer purchases SAF certificates in bulk from producers and resells them to smaller operators. This approach is intended to “de-risk” the process for customers who may lack the purchasing power to negotiate large fuel contracts independently.
Julien Manhes, Head of Sustainable Aviation Fuel at Airbus, highlighted the company’s objective to democratize access to green fuels:
“For a lot of smaller operators, getting access to SAF can be challenging… Airbus can simplify and derisk the process.”
To ensure transparency and prevent “double counting”, where two different parties might claim the same environmental benefit, the initiative utilizes a registry managed by the Roundtable on Sustainable Biomaterials (RSB). This certification ensures that once the carbon reduction is claimed by the HEMS operator, it cannot be claimed by the entity physically burning the fuel at the central hub. While the “Book and Claim” model solves the immediate logistical hurdles for HEMS operators, it faces a complex regulatory landscape. As of late 2025, major frameworks like the EU Renewable Energy Directive (RED) and the ReFuelEU initiative prioritize the physical supply of fuel at mandated airports. Consequently, “Book and Claim” systems are not yet fully recognized for meeting all national compliance targets, creating a temporary regulatory gap.
Furthermore, while this system reduces Scope 3 emissions for clients like the Catalan Department of Health, the cost of SAF remains significantly higher, often 2 to 8 times that of conventional jet fuel. The willingness of public health administrations to absorb these costs signals a shift in public tenders, where environmental compliance is becoming a non-negotiable requirement for government contracts.
The deployment in Catalonia serves as a proof-of-concept for the wider industry. Juan Carlos Gomez Herrera, representing the Catalan Administration, noted that the initiative aligns with their broader public health mandate, viewing environmental responsibility as an extension of immediate medical care.
By decoupling the physical fuel from its environmental attributes, Airbus and SAF Hélicoptères are demonstrating a viable pathway for decarbonizing decentralized aviation sectors that have previously been left behind by airport-centric green policies.
Sources: Airbus
New “Book and Claim” Model Brings Sustainable Fuel to Remote Air Ambulances
Overcoming the “Last Mile” Logistics Challenge
The Role of Airbus and Certification
AirPro News Analysis: The Regulatory Gap
A Model for Future Operations
Photo Credit: Airbus
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