As calls for action increase over the climate impacts of aircraft contrails, airborne research is intensifying with the expansion of two key projects in Europe and the US. In Germany, Lufthansa has started converting an Airbus A350-900 for use as a flying research laboratory as part of IAGOS-CARIBIC, a long-running European programme that uses commercial airliners to gather data on air quality for scientific evaluation. The A350 will be equipped with around 20 measuring instruments for a multi-year project beginning late next year to measure trace gases, aerosol and cloud parameters on selected long-haul flights. In the US, engine manufacturer GE Aerospace and NASA have just completed two flights with a Boeing 747 testbed aircraft to record three-dimensional imaging of contrails to better understand how they form and behave in certain conditions. The 747’s emissions were scanned using Light Detection and Ranging (LiDAR) technology installed on a following aircraft.

IAGOS (In-Service Aircraft for a Global Observing System) is a European programme established in 1994 to assess atmospheric composition, air quality and climate, using commercial jets as research platforms. There are currently 10 widebody Airbus A330 and A340 family jets from seven airlines deployed in the project, with another 10 having previously been used, again from seven participating airlines.  

The Lufthansa A350 selected for the IAGOS programme, registered D-AIXJ, is almost seven years old, and will add a new-generation airliner to the research fleet.

A measuring laboratory weighing two tonnes is being developed for the next phase of the programme, and once fitted with some 20 instruments, will be installed in the cargo hold of the A350 on selected scheduled flights from late 2025.

The onboard laboratory will be connected to the air intake system on the jet’s outer fuselage through permanently installed pipes, and used to measure over 100 trace gases, aerosol and cloud parameters from the ground up to the tropopause atmospheric region, at altitudes between nine and 13 kilometres.

The IAGOS programme is led by the Jülich Research Centre, one of Europe’s largest research organisations, which combines the expertise of global partners in weather services, airlines and the broader aviation sector.

The programme combines the complementary concepts of two research projects: MOZAIC (Measurement of Ozone, Water Vapour, Carbon Monoxide and Nitrous Oxides by Airbus In-Service Aircraft), which was funded by the European Commission between 1993 and 2004, and CARIBIC (Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrument Container).  

Lufthansa, which with Air France was an IAGOS launch partner in 1994, has gathered climate-related data for research on more than 35,000 of its passenger flights over the three decades.

Together with the Jülich Research Centre and Karlsruhe Institute of Technology, the Lufthansa Group has fitted a total of six Airbus aircraft with measuring equipment since the programme was inaugurated to collect information about atmospheric conditions during scheduled flights.

Lufthansa currently has two aircraft, an A330 and an A340, deployed in the programme, as well as another A330 from sibling airline Eurowings Discover.

On December 9, the Eurowings jet was used to gather climate data during a 10-hour, 45-minute flight from Frankfurt to Orlando, Florida. The information was collected continuously while the aircraft flew at an altitude of more than 10,000 metres (33,000 feet) over a distance of 7,600 km.

Other airlines currently participating in the programme are Taipei-based China Airlines, with two A330s, and Air Canada, Air France, Cathay Pacific, Hawaiian and Iberia, each with one A330.

After each flight, climate information gathered by the aircraft is sent automatically to the database of Centre National de la Recherche Scientifique in Toulouse, France, from where it is accessible for global research.

The data is currently used by about 300 organisations worldwide to provide fresh insights into climate development and atmospheric composition and help refine climate models and improve weather forecasting.

“We are proud to have been able to make a significant contribution to climate research for 30 years,” said Lufthansa Group’s Chief Technology Officer, Grazia Vittadini. “Through our commitment, we are helping to sustainably improve climate models and weather forecasts. Scientifically-sound findings are the basis for targeted measures on the path for more sustainable aviation.”

GE/NASA contrail research flights

In the US, GE Aerospace and NASA have built upon a 50-year collaboration by performing two research flights for their Contrail Optical Depth Experiment (CODEX) in which three-dimensional imaging was generated of contrails created by GE’s Boeing 747-400 Flying Test Bed aircraft.

The 747 was trailed by a G-111 aircraft from NASA’s Langley Research Centre in Virginia, which deployed Light Detection and Ranging (LiDAR) technology to scan the wake of the larger jet, enabling researchers to use new imaging to better understand how contrails form and behave.

During the flight tests, 3D images were generated of contrails from all four CF6 engines on the 747. GE Aerospace was also able to isolate the contrails from a single engine on the test jet.     

The flights expanded the company’s capabilities ahead of flight tests it is planning during this decade to assess the performance of new commercial aircraft engine technologies, including Open Fan, advanced combustion designs and other propulsion systems.  

“Understanding how contrails act in flight with the latest detection technology is how we move innovation forward,” said Arjan Hegeman, GE Aerospace GM of Future Flight Technology. “These tests will provide critical insight to advance next generation aircraft engine technologies for a step change in efficiency and emissions.”

Dr Rich Wahls, manager of NASA’s Sustainable Flight National Partnership, welcomed participation “on this first-of-its-kind flight experiment” in helping to reduce the impact of contrails.

“NASA is advancing the scientific understanding of contrails to improve our confidence in future operational contrail management decisions that consider overall climate impact and economic trades,” he said.

NASA, German Aerospace Centre (DLR) and contrail forecasting and management company SATAVIA, are also working together on atmospheric forecasting to identify the best conditions for studying the formation of contrails. SATAVIA was recently acquired by Aerospace Carbon Solutions, a division of GE Aerospace.

In this collaboration, DLR will help to identify the altitude and dimensions of contrail-forming regions, so that flight tests can be conducted using the LiDAR technology to improve contrail prediction, while SATAVIA will use the flight test results to validate and improve its numerical weather prediction capability, used to forecast contrail formation conditions.

At this year’s Farnborough Airshow, the chief technology officers of GE Aerospace, Boeing, Airbus, Dassault, Rolls-Royce, RTX and Safran called for government support to expand research that enhances scientific understanding of aviation non-CO2 effects such as contrails, nitrogen oxides, sulphur, aerosols and soot.

Top photo: The first IAGOS system has been in use on a Lufthansa Airbus A340-300 since 2011

Bottom photo: GE Aerospace’s 747 Flying Test Bed

Tony Harrington

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UK regional airline Loganair is to partner with emerging Swedish aircraft maker Heart Aerospace to explore potential uses for hybrid-electric aircraft. Through their alliance, the two will establish use cases across the airline’s UK network focusing on Heart’s evolving ES-30, a 30-seat aircraft which the company expects to enter service by the early 2030s. The companies will engage with the Scottish and UK governments and airports to advocate the benefits of electric-powered flights, and the airline will join Heart’s industry advisory board, members of which include airlines, airports, aircraft lessors and governments. Meanwhile, in a new test programme in the US involving electric powertrain manufacturer magniX and NASA, two of the four engines on a De Havilland Dash 7 commuter plane will be replaced with electric motors to help evolve hybrid-electric propulsion for use on large turboprop aircraft.          

Glasgow-based Loganair serves a network of more than 30 destinations across the UK and additional points in Ireland, Norway and Denmark with a fleet of 44 aircraft, ranging from nine-seat Britten-Norman Islanders and 19-seat De Havilland Twin Otters to 49-passenger Embraer ERJ jets and 70-seat ATR 72-600 turboprops. The partnership with Heart introduces the ES-30 as a future option, with a fully electric zero emissions range of 200 kilometres, an extended hybrid flying range of 400 kilometres with up to 30 passengers, and capacity to fly up to 800 kilometres with 25 passengers, with all operating settings including typical airline reserves. 

“This is a very exciting and significant moment for Loganair and for the future of sustainable UK regional flying,” said the airline’s CEO, Luke Farajallah. “This exclusive collaboration with Heart Aerospace brings together two organisations who share a passion to see aviation emissions reduce in a realistic and meaningful way, and we definitely see the ES-30 as being a strong contender to emerge as one of the leaders in this space.

“We are very proud of our environmental work and achievements to date, and we see this as the next logical step along the path to a greener future for UK regional aviation.”

He said the airline’s newly appointed Director of Safety and Sustainability, Rebecca Borresen, who commences with the company on 1 October, would be heavily involved in the partnership with Heart.

Simon Newitt, President and CCO of Heart, welcomed the partnership with Loganair. “We’re thrilled to partner with them to bring cleaner air travel to the UK,” he said. “This collaboration is an important step in our mission to make air travel more sustainable and we look forward to bringing clean and convenient solutions to Loganair in support of its ambitious goal to achieve net zero emissions across its operations by 2040.”

In the US, electric propulsion developer magniX has revealed a De Havilland DHC-7 (Dash 7) demonstrator aircraft in special livery as part of NASA’s Electrified Powertrain Flight Demonstration programme (EPFD) to support the introduction of both battery electric and hybrid electric aircraft into commercial fleets by 2030.

The Everett, Washington-based magniX has been progressing the project since 2021 when it secured a $74.3 million contract from NASA and is leading the conversion of the four-engine Dash 7 from Canadian operator Air Tindi to a testbed for electric motors.

Initially, magniX will replace one of the Dash 7’s turbine engines with a magni650 electric propulsion unit, with a second to follow in the next stage of the programme. They will be powered by a large battery energy storage system.

In February magniX achieved the Preliminary Design Review, which established the design for the installation of electric powertrains on the Dash 7, and in April a magni650 electric engine completed the first phase of testing at NASA’s Electric Aircraft Testbed (NEAT) facility in Ohio. Baseline tests were then performed with the aircraft to generate performance data ahead of the installation of the magniX electric powertrains.

“As EPFD makes outstanding progress, magniX and NASA are proving the feasibility of electric propulsion for commercial flight,” said magniX CEO Reed Macdonald. On a typical regional flight in the US, extending about 200 miles (322 kilometres), the company estimated that a hybrid aircraft would achieve fuel savings of up to 40%.

Ben Loxton, magniX VP of the EPFD programme and Electric Storage Systems, said the project with NASA would also demonstrate that sustainable flight was achievable using existing aerospace technology. “The programme is accelerating its readiness for entry into service, prioritising safety and the highest standards of performance.”

Robert Pearce, Associate Administrator of NASA’s Aeronautics Research Mission Directorate, said EPFD would not only deliver more sustainable aviation, but also greater air transport access to more communities in the US. “Hybrid electric propulsion on a megawatt scale accelerates US progress toward its goal of net zero greenhouse gas emissions by 2050,” he said, “benefiting all who rely on air transportation every day.”

Image: Heart Aerospace’s ES-30 in Loganair livery

Tony Harrington

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Boeing has selected engine maker Pratt & Whitney and its sibling company Collins Aerospace as partners in its groundbreaking X-66A sustainable aircraft programme, in which a former passenger jet will be converted to test the airframer’s futuristic Transonic Truss-Braced Wing (TTBW). The transformation of the 1995-built MD-90 twinjet is part of NASA’s Sustainable Flight Demonstrator Project, which is tasked with trialling a range of new technologies to increase aircraft efficiency and reduce carbon emissions. In a radical retrofit, Boeing will remove the plane’s low, rear-swept wings and instal high-mounted, long, thin wings, supported by diagonal trusses. The new, forward-swept wings are designed to reduce aerodynamic drag, improving fuel efficiency by up to 10%, while the addition of Pratt & Whitney’s GTF (geared turbofan) engines, and new nacelles and engine accessories from Collins, together with other initiatives, could improve total efficiency by as much as 30%. Both companies, part of the RTX aerospace group, will also support ground and flight tests of the experimental plane, which are scheduled to commence in 2028.    

The Transonic Truss-Braced Wing programme is a key element of broader US efforts to decarbonise emissions from commercial aircraft, and will help inform the design of future narrowbody airliners. The former Delta Airlines MD-90 to be used in the programme recently flew from Victorville, California, where it was stored, to nearby Palmdale for modification.

NASA estimates that single-aisle airliners generate more than 50% of global emissions from aircraft, but says technical and economic risks often prevent promising technologies from proceeding to production. It is partnering with the aerospace industry on the X-66A programme to help develop and flight test an advanced airframe and new technologies to improve fuel efficiency while reducing emissions, and to gather ground and flight test data to validate the outcomes.

“We are excited to be working with Boeing on the X-66A Sustainable Flight Demonstrator, making critical contributions to accelerate aviation towards its 2050 net-zero greenhouse gas emission goal,” said Ed Waggoner, Deputy Associate Administrator for Programs in the NASA Aeronautics Research Mission Directorate.

The agency said the research results would help the aerospace industry to progress development of next-generation single-aisle aircraft which meet the goals of the US Aviation Climate Action Plan.   

“This marks an important step in the Sustainable Flight Demonstrator project, advances Boeing’s commitment to sustainability and brings us closer to testing and validating the TTBW design,” said Dr Todd Citron, Boeing’s Chief Technology Officer.

“The X-66A is NASA’s first experimental plane focused on helping the US achieve its goal of net-zero aviation greenhouse gas emissions,” he said. “The learnings from the Sustainable Flight Demonstrator and the partnership with NASA are important elements in the industry’s efforts to decarbonise aviation. We’re grateful for the support from RTX on this critical effort.”  

Geoff Hunt, Pratt & Whitney’s SVP Engineering and Technology, said NASA’s Sustainable Flight Demonstrator programme highlighted how collaboration across the aerospace sector could help expedite the transition to net zero emission flight.

“We’ll work with Boeing to apply GTF engines to the X-66A and help demonstrate the potential of its pioneering truss-braced wing design,” he said. Pratt & Whitney’s geared fan engines, introduced into service in 2016, are designed to offer up to 20% better fuel efficiency than conventional powerplants and certified to operate with sustainable aviation fuel.

Further improving the efficiency of the testbed aircraft will be lightweight engine nacelles, produced by Collins using durable composite and metallic materials. It will also provide control system components for the GTF engines to be used on the testbed aircraft, including their heat exchangers, integrated fuel pump and starter, and air turbine starter and electronic controls.

“Collins has as long history of successful partnerships with NASA, Boeing and Pratt & Whitney, with decades of experience pushing the boundaries of innovation in aerospace,” said the company’s SVP Engineering and Technology, Dr Mauro Atalla. “Now, as part of the Sustainable Flight Demonstrator programme, we will work together to demonstrate new technologies and systems to support the next generation of low-emission single-aisle aircraft that will play an integral role in reducing the environmental footprint of the aviation industry.”    

RTX is also collaborating with NASA on other sustainable aviation projects, including Hybrid Thermally Efficient Core (HyTEC) and Hi-Rate Composite Aircraft Manufacturing (HiCAM), as well as progressing its engines to operate with 100% unblended SAF, hybrid-electric power and hydrogen fuel.

Image (Boeing): A render of the X-66A

Tony Harrington

Correspondent

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Boeing will partner with NASA to build, test and fly a full-scale demonstrator aircraft, designed to validate technologies which could cut by up to 30% the fuel consumption and emissions of future single-aisle aircraft, compared to today’s most-efficient models. The Transonic Truss-Braced Wing prototype will be a narrowbody, twin-engine aircraft with extra-long thin wings, high-mounted and stabilised by diagonal struts to produce less aerodynamic drag than current designs. The concept is the culmination of more than a decade of development by Boeing, NASA and industrial partners, which has included detailed digital modelling and wind tunnel testing. NASA will invest $425 million and Boeing and its industrial partners an estimated $725 million in the seven-year Sustainable Flight Demonstrator programme. It is enabled under a Funded Space Act Agreement through which NASA can leverage private industry knowledge and experience to progress aviation efficiency initiatives.

NASA said single-aisle aircraft were the backbone of many airline fleets, which, due to their high-cycle utilisation, are responsible for almost half of global emissions from aviation. They account for 75-80% of fleet demand forecast by Boeing and its European rival Airbus during the next 20 years. Boeing believes the use of longer, higher wings could eventually enable the use of advanced propulsion systems that are limited by restricted underwing space on current low-wing aircraft.

“If we are successful,” said NASA Administrator Bill Nelson, “we may see these technologies in planes that the public takes to the skies in the 2030s.”

 In addition to the funding, NASA will contribute technical expertise and facilities to the demonstrator aircraft programme, though it will not procure an aircraft or other hardware for its missions. It will also gain access to ground and flight data to help validate the airframe configuration and associated technologies featured on the test aircraft.

“NASA plans to complete testing for the project by the late 2020s, so that technologies and designs demonstrated by the project can inform industry decisions about the next generation of single-aisle aircraft that could enter into service in the 2030s,” the agency said. “The Sustainable Flight Demonstrator will help the United States achieve net zero carbon emissions from aviation by 2050 – one of the environmental goals articulated in the White House’s US Aviation Climate Action Plan.”

Bob Pearce, NASA Associate Administrator for the Aeronautics Research Mission Directorate, said the agency was working towards “an ambitious goal of developing game-changing technologies” as part of a broader drive by the aviation sector to achieve net zero carbon emissions by 2050.

“The Transonic Truss-Braced Wing is the kind of transformative concept and investment we will need to meet those challenges and, critically, the technologies demonstrated in this project have a clear and viable path to informing the next generation of single-aisle aircraft, benefiting everyone that uses the air transportation system,” he said. 

Together with other advancements in propulsion systems, materials and systems architecture, the technologies test-flown on the new demonstrator aircraft are expected to deliver the up to 30% reduction in fuel burn and emissions compared to the most efficient single-aisle aircraft in service today.

Boeing’s latest global forecast, the 2022-2041 Commercial Market Outlook, estimates a requirement for 41,170 new aircraft over the survey period. Of these, it forecasts that 30,880, or 75%, would be single-aisle aircraft, the focus of its new collaboration with NASA, “as domestic and inter-regional travel continue to drive the sector’s near-term recovery and continued future growth.”  This aircraft segment also represents 75% of Boeing’s 10-year forecast, accounting for 14,620 of the total 19,575 aircraft the company estimated would be needed in that period. The equivalent forecast by European rival Airbus estimates a total demand for 39,490 new passenger and freight aircraft during the same 20-year timeframe, but forecasts that 31,620, or 80%, would be typically single-aisle.

Boeing has previously worked with NASA and industry partners on other advanced aviation concepts. “We’re honoured to continue our partnership with NASA and to demonstrate technology that significantly improves aerodynamic efficiency, resulting in substantially lower fuel burn and emissions,” said Boeing’s Chief Technology Officer, Todd Citron. “Boeing has been advancing a multi-pronged sustainability strategy, including fleet renewal, operational efficiency, renewable energy and advanced technologies to support the US Aviation Climate Action Plan, and meet the industry objective of net zero carbon emissions by 2050. The Sustainable Flight Demonstrator builds on more than a decade of NASA, Boeing and our industry partners’ investments to help achieve these objectives.”  

The Sustainable Flight Demonstrator project is part of NASA’s Integrated Aviation Systems Program, and one of the main elements of the Sustainable Flight National Partnership, dedicated to developing new technologies for more sustainable air transport. NASA has also worked with partners in other segments of the air transport industry, including electric aviation start-up Ampaire and aircraft engineering and modification group Ikhana on as project to convert turboprop DHC Twin Otter aircraft to hybrid electric propulsion.

Image: Boeing concept of commercial aircraft families with a Transonic Truss-Braced Wing configuration from the Sustainable Flight Demonstrator project

The aviation sector’s efforts to mitigate anthropogenic climate change have predominantly focused on CO2 emissions. However, the non-CO2 effects created by aircraft flying at cruise altitude have been found to be larger than the impact from CO2 alone, and estimated at two thirds of the net radiative forcing from aviation, but this has been largely unaddressed by the airline industry and policymakers. This is mainly due to uncertainties over the scientific understanding through a lack of reliable data and how best to overcome the effects through aircraft operations, as well the inability to agree on what policy measures should be introduced to deal with the issue. Susan van Dyk reports on a recent conference hosted by the Royal Aeronautical Society’s Greener by Design Specialist Group, in collaboration with German aviation research organisation DLR, which presented the latest scientific studies on non-CO2 impacts and potential strategies and policies for mitigation.

Non-CO2 climate effects come from NOx emissions, soot from fuel combustion, water vapour and formation of persistent contrails (contrail cirrus) which contribute to increased cloudiness. Unlike CO2 impacts, non-CO2 effects depend on the location and time of emissions and this plays a role in selecting suitable mitigation steps. The climate impact of aviation from non-CO2 effects can be mitigated through various measures, including new engine technologies to reduce emissions, use of sustainable aviation fuel and air traffic management (ATM) strategies.

Contrail cirrus formation has the largest positive net (warming) effective radiative forcing (ERF) effect, followed by CO2 and NOx emissions. Contrail cirrus alone contributes >50% of the net ERF impact and is therefore an important target for mitigation of non-CO2 effects. Contrails are formed by aircraft through condensation of the water vapour from fuel combustion. While most contrails disappear relatively quickly, persistent contrails form cirrus clouds under certain temperature and humidity conditions. The cirrus clouds have some cooling effect by reflecting the sunlight, but also has a warming effect by trapping heat radiating from the earth’s surface.

Mitigation through flight diversion aims at avoidance of ice supersaturated regions (ISSR) where contrail cirrus formation has the greatest impact. The net warming effect of contrail cirrus is also greatest between 3pm until 6am and flight diversion is focused on this time period. Contrail avoidance through diversion of flights and ATM measures could represent a fast way (hours or days) to reduce the impact of aviation on the earth radiation budget.

Flight diversion and contrail avoidance is the current focus of live trials in the Maastricht Upper Area Control (MUAC). Dr Rudiger Ehrmanntraut, Senior Project Manager at Eurocontrol, explained that vertical diversion, 2000 ft above the ISSR or 2000 ft below the ISSR during the time period of 4pm to 6am, is the main approach during this project to avoid persistent contrail formation. A crucial prerequisite, he said, is the accurate prediction of ISSRs and potential areas of persistent contrail formation using meteorological data.

Dr Marc Stettler from Imperial College London has been carrying out research on the extent of flight diversion that will be required. His work has demonstrated that only 2.2% of flights account for 80% of the total net energy forcing due to contrails. Therefore, total fleet diversion is not necessary to achieve a significant impact, he argued. By diversion of 1.7% of flights, contrail radiative forcing can be reduced by 59%. If flight diversion is used simultaneously with cleaner engines, the contrail radiative forcing can be reduced by 92% (which amounts to 57% of the total radiative forcing).

However, flight diversion increases fuel consumption and CO2 emissions. Professor Ian Poll from Cranfield University quantified this fuel penalty for avoiding ISSRs and concluded the overall extra fuel burn was insignificant. If an aircraft is diverted 2000 ft above the ISSR, there is a 1.5% increase in fuel, and 1.4% when diverted 2000 ft below. However, this fuel penalty is only for the duration of the diversion, not the whole flight. A reduction in altitude results in a reduction in NOx emissions as an added benefit.

A significant contributor to formation of persistent contrails is the creation of soot as a result of fuel combustion. Studies at DLR by Professor Christiane Voigt’s research group show that 80% of soot particles form ice particles, which leads to persistent contrails. Lower soot formation will impact contrails and contrail cirrus formation and reduce some of the climate impacts of non-CO2 emissions. Reduction of soot particles causes a non-linear decrease in radiative forcing and it has been demonstrated that a 50-70% reduction in ice particles leads to 20-40% reduction in contrail radiative forcing. According to Voigt’s research, the main cause of soot formation is the aromatics in jet fuel, so reducing soot emissions can be achieved by decreasing the aromatic content. She said an effective way of reducing the aromatic content is through the use of sustainable aviation fuel (SAF). Currently available SAF, based on hydrotreatment of fats, oils and greases (called HEFA), is almost entirely composed of paraffins and cycloparaffins with virtually zero aromatics.

ASTM jet fuel specifications require aromatics at a minimum of 8.5% by volume and a maximum of 25%. A minimum aromatic content is considered essential to maintain seal integrity in the engine and aircraft and prevent seals from leaking. Current certification under ASTM D7566 only permits a 50% blend of HEFA with conventional fossil jet fuel and the blend must contain at least 8.5% aromatic content by volume. An earlier study, published in Nature in 2017, was carried out with a 50% blend of HEFA and demonstrated a reduction in the particle number and mass emissions immediately behind the aircraft by 50-70%. It concluded the effect was mainly due to reduced aromatics content and reduced soot particle formation.

Recent research as part of the ECLIF3/ND-MAX campaign, a collaboration between DLR and NASA, has also confirmed a strong reduction in soot emission indices by using low aromatic fuels. According to Voigt, her research has shown naphthalenes are more efficient soot precursors compared to monocyclic aromatics and decreased naphthalene content decreased the soot formation. She emphasised that stronger reductions in aromatics in jet fuels are needed to reduce persistent contrails and this will require changes in certification standards to permit fuel with lower than 8.5% aromatics. In addition, certification should also permit the use of 100% alternative jet fuels rather than the current maximum of 50%.

Rolls-Royce and Airbus recently announced what they say is the world’s first in-flight emissions study using 100% sustainable aviation fuel (see article). The ongoing Emission and Climate Impact of Alternative Fuels (ECLIF) project studies the impact of 100% SAF on aircraft emissions and performance. Paul Madden, Energy Emissions Expert from Rolls-Royce, told the conference there had been no operability issues or seal leakage problems as a result of using 100% SAF in the aero engine manufacturer’s engines, although he conceded this may not be the case in older engines.

Madden also explained some of the modified engine operations that Rolls-Royce is implementing, such as the lean burn engine, which can improve NOx emissions and soot formation. NOx emissions are not reduced through the use of SAF, and cleaner burning engines will be the main approach for mitigation.

Stephen Arrowsmith, Chief Expert on Environmental Protection at the European Aviation Safety Agency (EASA), highlighted the potential policy measures that could be implemented to address non-CO2 impacts as published in a recent EASA report (see article). The EU Emissions Trading System (EU ETS) currently only addresses CO2 emissions through policy.

The report divided policy options into three categories: financial/market-related, fuel and ATM. Financial measures suggested include a monetary charge levied on aircraft NOx emissions on one side and/or the inclusion of such emissions under the EU ETS on the other. Potential fuel-related measures could encompass the reduction of aromatics within fuel – leading to cleaner fuel burn and reduced nvPM emissions – and the mandatory use SAF. Both measures would target soot emissions and associated formation of contrail cirrus clouds.

Proposed measures in the ATM category are avoidance of ice-supersaturated areas and a climate charge. Flight diversions to avoid ice supersaturated areas would reduce the formation of contrail-cirrus clouds, while a climate charge would address all non-CO2 effects (NOx, water vapour, soot, sulphates, contrails). Several research issues would have to be addressed before these measures could be implemented, said Arrowsmith. Fuel-related measures could potentially be implemented in the short term (2-5 years), while other measures will likely take longer to implement (5-8 years) due to outstanding research questions, he believes.

The conference succeeded in highlighting the important, but somewhat overlooked, climate impact of non-CO2 effects from aviation. It demonstrated this impact can be significantly mitigated through modified air traffic management and use of sustainable aviation fuels with low aromatic content.

Photo: NASA’s ‘airborne laboratory’ flies close behind the DLR A320 Advanced Technology Research Aircraft (ATRA), flying through the Airbus’ exhaust plume. On board, scientists measure the composition of the exhaust stream and analyse the effects of biofuels like HEFA on the formation of soot particles and ice crystals (credit: DLR/NASA/Friz)

About the author

Susan van Dyk

A Research Associate at the University of British Columbia in Canada, Susan is a scientist and independent researcher specialising in biofuels and renewable energy, with a particular focus on sustainable aviation fuels. She has published numerous peer-reviewed papers and been the author of multiple reports on drop-in biofuels and SAF. She has worked on a number of Canadian biojet initiatives. Susan can be contacted through her website https://www.svdconsulting.ca/

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