A new US government roadmap report on measures to decarbonise transportation says the administration must work towards “multi-beneficial climate protection provisions” in its bilateral and multi-lateral aviation agreements, as part of broader global engagement to progress sustainable aviation. It says the government also must pursue ambitious international standards to incentivise the most effective technologies to combat aircraft emissions, negotiate internationally to strengthen ICAO’s aircraft CO2 emissions standards, maintain the environmental integrity of ICAO’s CORSIA carbon offsetting scheme for international aviation and support the implementation of medium- and long-term goals adopted by the UN agency in 2022. The international initiatives are contained in a roadmap report by four federal agencies to reduce emissions across the transportation sector. Drop-in sustainable fuels are seen as the most viable pathway for the rapid decarbonisation of air transport.
The Department of Energy (DOE), Department of Transportation (DOT), Environmental Protection Agency (EPA) and Department of Housing and Urban Development (HUD) have signed a joint memorandum of understanding to progress ‘The US National Blueprint for Transportation Decarbonization’, which will engage all levels of government across the country. Together, the agencies will create a decarbonisation strategy covering all US transport modes and detailing specific actions required to meet 2030 interim targets, as well as intensifying international actions by the US to decarbonise air transport.
The report says transport is now the largest source of greenhouse gas emissions in the US, with aviation responsible for 11% of the sector’s output. As well as the need to accelerate development and distribution of sustainable aviation fuels, it highlights subsidies for new aircraft technologies, continued improvements in US airspace management and greater focus on reducing non-CO2 emissions from flights as key areas for action. It also acknowledges electric and hydrogen propulsion systems will contribute to cleaner aviation but before 2050 they will only be suitable for regional passenger or freight flights.
“The combustion of jet fuel from domestic and international aviation is responsible for more than 10% of total transportation greenhouse gas emissions in the US,” says the report. “The CO2 emissions from domestic commercial flights are roughly comparable to the CO2 emissions of international commercial flights coming to and leaving from the US.”
The report prioritises incentives for low-emission aviation innovations using new and breakthrough technologies, or access to proven technologies from other transportation sectors.
New aircraft and engine technologies were highlighted as key drivers of aviation decarbonisation. Through the Sustainable Flight National Partnership (SFNP) announced last year and led by NASA Aeronautics, the government will engage with the aerospace industry to demonstrate technologies that are expected by 2030 to improve fuel efficiency by up to 30% over today’s best-performing aircraft. By then, aircraft would also be able to operate using 100% SAF, double the amount currently permitted.
“With investments by industry and the federal government, new, more fuel-efficient aircraft could be introduced,” says the Blueprint report. “The SFNP will conduct ground and flight tests to demonstrate technologies with step-change improvements in environmental performance.” Among the concepts being tested or explored through the SFNP are new wing and advanced turbine engine concepts, and a technology demonstrator ‘X-plane’ to test “an ultra-efficient aerodynamic design, and possibly other new technologies”.
But, it warns: “An increase in aviation demand could also lead to additional congestion and inefficient air traffic management-related fuel usage. Without continued investment in operational improvements, excess per-flight fuel usage is expected to increase. Further optimisation of surface, take-off, cruise and landing operations is possible with continued infrastructure investments and development of improved operational concepts. Enhanced data quality and information distribution can enable operators to fly more fuel-efficient trajectories in US-controlled airspace, especially during the cruise phases of flights.”
The report reiterates the US government’s view that sustainable aviation fuels will be critical to the long-term decarbonisation of air transport, due to their compatibility with existing infrastructure, aircraft and engines, and their ability to reduce lifecycle greenhouse gas emissions by at least 50% compared to conventional jet fuels – potentially 100% if low-carbon technologies are deployed in producing the fuels.
It rules out the use of battery electric or hydrogen propulsion systems as realistic options to cut emissions of medium to long haul flights, which generate most of the aviation sector’s carbon emissions. “These technologies can play an important role in the coming decades by decarbonising short-distance flights and dedicated regional cargo routes,” it says. “At present, flights less than 500 nautical miles (926 km) represent 50% of operations, but only 15% of total fuel usage. Conversely, flights greater than 1,000 nautical miles (1,852 km) represent 20% of operations and 65% of total fuel usage.
“Since the majority of aviation CO2 emissions stem from long-haul operations and fleet turnover is slow – an average of 30 years for most aircraft – drop-in SAF is the most viable pathway for rapid decarbonisation of the aviation sector.”
Under the government-industry SAF Grand Challenge, a goal has been established to increase US SAF production to at least 3 billion gallons per year by 2030, with the aim of producing about 35 billion gallons by 2050, a level at which the government predicts would decarbonise the aviation sector “almost entirely”.
Beyond CO2 emissions, the report also acknowledges air transport creates high altitude emissions and aviation-induced cloudiness which could impact the climate. “Additional research is needed to quantify the greenhouse gas impact from these factors and to understand how SAF, improved technologies and operational procedure changes might mitigate climate impact without increasing CO2 emissions from added fuel usage.”
Photo: Washington Reagan National