Federal Programs Advancing Sustainable Commercial Aircraft and Engine Technologies | Article

The U.S. government, energy companies, academia, and the aviation industry—including airlines, aircraft and engine manufacturers, and suppliers—are all engaged in technological and operational improvements to reduce the environmental and climate impact of the country’s commercial aviation sector. Federal agencies play a significant role in this national effort, from the Department of Transportation and the Federal Aviation Administration (FAA) to the National Aeronautics and Space Administration (NASA), the Environmental Protection Agency, and the Departments of Agriculture, Defense, and Energy.

FAA, NASA, and industry groups are working together as a part of the Sustainable Flight National Partnership to develop engine and aircraft technology that would produce a 25 to 30% lower fuel burn relative to the current best-in-class aircraft and reduce engine and aircraft noise. Three major programs underway in pursuit of this goal are the Continuous Lower Energy, Emissions, and Noise (CLEEN) Program; the Center of Excellence for Alternative Jet Fuels and Environment (ASCENT Center of Excellence); and NASA’s flight testing program. These government partnerships and federal cost sharing make it possible for corporate participation in development projects that have both significant technological risk and the potential for large improvements in fuel efficiency, reduced particulate and nitrogen oxide emissions, and noise reduction.

Continuous Lower Energy, Emissions, and Noise (CLEEN)

The CLEEN program, a set of FAA public-private partnerships to accelerate the development of new sustainable aircraft technologies, began with CLEEN I in 2010. CLEEN II followed in 2015, and the FAA announced the program’s third phase in September 2021. Ten corporate partners joined the initiative over the course of the three phases, including engine and aircraft manufacturers Boeing, General Electric Aviation, and Honeywell Aerospace. Partners must match or exceed FAA funding to participate in the program, which leveraged $388 million from the private sector during phases one and two, while the FAA invested $225 million. The FAA is planning a fourth phase of the program for 2025 through 2029.

Projects focus on issues like developing advanced wings constructed with lighter-weight and stronger composite materials and flight management system algorithms that calculate the most efficient cruise altitudes, speeds, and descent profiles. CLEEN III projects are targeting reductions of particulate matter in jet exhaust, aiming for a 20% improvement over the current international standard. Aircraft electrification is also on the research agenda, with CLEEN projects investigating what types of flights are best suited for electrification.

Technologies from CLEEN I are incorporated in the fleet today. Phase two results are expected to be operational by 2026, and CLEEN III results by 2031. According to the FAA, technologies from the first two phases of the program will reduce commercial aviation fuel consumption by 51.1 billion gallons through 2050, cut carbon dioxide emissions by 404 million metric tons, and generate substantially lower nitrogen oxide and soot emissions from aircraft. CLEEN projects also resulted in better analysis and design tools that companies can use in technology development going forward.

Center of Excellence for Alternative Jet Fuels and Environment

The Center of Excellence for Alternative Jet Fuels and Environment, also known as the Aviation Sustainability Center (ASCENT), advances partnerships with both universities and the private sector to reduce the environmental impact of aviation, including through the large-scale development of sustainable aviation fuels. In operation since 2013, ASCENT is funded by a combination of federal agencies, including the FAA, NASA, and the Department of Energy. The program is co-led by Washington State University and the Massachusetts Institute of Technology (MIT), and includes 14 additional universities and more than 55 private sector stakeholders. Just over 70 ASCENT projects are in progress, and 30 have been completed. They cover a range of issues, including noise assessment and mitigation, aviation emissions and air quality, aircraft technology for greater efficiency, improved operations, alternative fuels, supersonic commercial flight, and modeling and assessment tools for evaluating aircraft performance in various phases of flight while using sustainable aviation fuel. Projects also explore regulatory and policy needs. For example, MIT and the Georgia Institute of Technology have undertaken a study to develop stricter airworthiness standards to reduce aircraft carbon dioxide emissions and noise.

NASA’s Flight Testing

NASA carries out flight testing by working with aircraft manufacturers to modify existing airplanes or by designing and building test aircraft. NASA designates these experimental planes using an “X” with a number. In January 2023, NASA announced a partnership with Boeing to develop and produce a new experimental aircraft, the X-66A, through the Sustainable Flight Demonstrator project. The X-66A will test a new efficient long and slender wing design and supporting trusses called the Transonic Truss-Braced Wing Design (TTBW). According to Boeing, the TTBW—combined with advances in propulsion, lighter aircraft materials, and improved aircraft systems architecture—could reduce aircraft fuel consumption and emissions up to 30% over today’s most efficient single aisle airliner.

Rendering of the sustainable flight demonstrator X-66A. Credit: NASA

The FAA projects that U.S. commercial aviation will produce close to 500 million tons of carbon dioxide annually by 2050, assuming the use of current aircraft technology without the deployment of new abatement strategies. The projection is reduced to approximately 340 million tons with the deployment of new aircraft and technology improvements developed in programs such as CLEEN and ASCENT. Additional reductions in emissions are projected through increased operations efficiency from new air traffic management technology and the adoption of sustainable aviation fuel. Federal agency investments and partnerships are key to adequately reducing greenhouse gas emissions in the commercial aviation industry. The remaining articles in this series will examine public and private sector programs creating more efficient air traffic management, and the production and use of sustainable aviation fuel (SAF).

Author: Jeff Overton