Sustainable aviation: How Raytheon Technologies is working to cut carbon emissions

"Aviation has always been about big challenges – getting that big piece of metal in the air and making it as safe as possible. Now the next challenge we've got is, how do we make it more sustainable?" said LeAnn Ridgeway, chief sustainability officer at Collins Aerospace, a Raytheon Technologies business.

Engineers have worked steadily to reduce fuel burn throughout the history of aviation, she said, but the adoption of the 2050 goal by organizations including the Air Transport Action Group and the International Air Transport Association make it clear that "we've got to go from being evolutionary to being revolutionary."

Improving engine efficiency

The net-zero goal will require improving fuel economy across all aircraft, but the greatest effect will come from large engines. About 80% of current emissions come from long-range flights, or those that travel more than 1,000 miles.

Pratt & Whitney, a Raytheon Technologies business, is making revolutionary leaps in this area. In 2022, the business introduced the GTF Advantage engine, calling it "the world's most fuel efficient and sustainable single-aisle aircraft engine." It improves upon the performance of the original Geared Turbofan engine and far outpaces the previous generation of engines, offering a 17% reduction in fuel consumption and CO2 emissions.

"As engine manufacturers, we often take our products and make them better incrementally. We develop and acquire technology, then it comes to the point where we do something very significant, which is what we did with the GTF," said Graham Webb, Pratt & Whitney's chief sustainability officer.

The engine's signature feature is its architecture – specifically, its larger-diameter fans and smaller-diameter, higher-pressure turbomachinery. Future versions will tap into the benefits of that design even further, Webb said.

Another pathway to greater efficiency is to enable higher gas temperatures in the turbine section. That requires novel high-temperature materials such as the ceramic matrix composites being researched and developed at a new Pratt & Whitney facility as well as advanced manufacturing of cooling circuits to keep key parts of the engine below critical temperature thresholds.


Chart showing 2%

the amount of global emissions that come from the aviation industry

chart showing 80%

the amount of emissions that come from long-range flights

the amount of increased fuel economy from the original GTF engine

Chart showing 50%

the amount of reduction in regulated emissions from the original GTF engine

Advancing hybrid electric propulsion

The aviation industry is adopting what has already been a great success story for automotive manufacturers: the hybrid electric engine, which can deliver fuel economy in large commercial aircraft.

At the 2022 Farnborough International Airshow, Pratt & Whitney and Collins Aerospace announced the development of a new hybrid electric demonstrator that could be adapted to a variety of aircraft including high-speed eVTOLs, regional turboprops and single-aisle airliners. The project, known as the Scalable Turboelectric Powertrain Technology Demonstrator, will include a high-efficiency turbogenerator; energy storage; power electronics and modular, electronically driven propulsors.

"We're going to start small, looking at the advanced air mobility market space, the eVTOLs, 150 to 500 kilowatts, and then growing that up into the megawatt class," Webb said.

In a separate initiative, Pratt & Whitney has been awarded a contract from NASA to collaborate with Penn State University, Georgia Tech and Howard University on the design of a gas turbine engine that could power hybrid electric single-aisle, medium- and short-haul aircraft. Pratt’s contributions to that project include advanced modeling and simulation, as well as experiments on turbines.

A third project aims to build a hybrid electric demonstrator aircraft the size of a regional plane, under a $163 million government-supported effort in Canada. Pratt & Whitney is the propulsion system provider and will focus on the engine design, Collins Aerospace will provide a 1-megawatt electric motor and motor controller, and further support will come from the Raytheon Technologies Research Center.

The team's approach is to use the electrical system to help power the energy-intensive taxi and takeoff stages of flight, then switch to the thermal engine for cruising, where it is most efficient. The goal: a 30% reduction in fuel burn and CO2 emissions.

The project "really marries the best of both," electrical and thermal technologies, Webb said. "With our models, it's going to be a high-value-proposition technology."


Supporting sustainable aviation fuels

Reducing fuel burn is only one part of the solution. Another is to redefine fuel itself.

Sustainable aviation fuel, or SAF, is an alternative to fossil fuels, and Webb called its use "a key component of the industry's commitment to net-zero carbon emissions."

SAF includes biofuels, which are made from agricultural products that absorb carbon dioxide before they're harvested. On a net basis, these fuels have the potential to reduce CO2 emissions by up to 80%.

Other SAF would include e-fuels, where renewable energy from wind, solar or nuclear power is used to create hydrogen, which is then turned into jet fuel through chemical processes.

Today, SAF makes up less than 0.1% of global jet fuel consumption. Using it at scale could cancel out the anticipated net growth in emissions. The GTF Advantage has demonstrated it can run entirely on sustainable aviation fuels, with a successful test that used pure hydrotreated vegetable oil fuel, rather than a blend of SAFs and conventional jet fuel.

Pratt & Whitney is working to validate its other engines to do the same, and it is collaborating with the Commercial Aviation Alternative Fuels Initiative and ASTM International to help meet that goal.

The effort to adopt SAF in aviation goes well beyond the industry. It will require energy companies to build the necessary production infrastructure and governments around the world to encourage that development.


chart showing 80%

the potential amount of CO2 reduction from SAF

SAF's share of global jet fuel consumption today

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the amount of SAF cleared to be mixed into Jet A fuel today

the amount of SAF that planes will be cleared to run on in the future

Developing hydrogen propulsion

One alternative fuel that has drawn significant attention is hydrogen, which produces no carbon emissions when it is burned.

Aircraft manufacturers are laying out plans for hydrogen-fueled aircraft to enter service in the next 10 to 20 years, and Raytheon Technologies is participating in U.S. Department of Energy research and development projects to test hydrogen as an effective zero-carbon option. 

In one of those projects, the company will validate the use of hydrogen and hydrogen blends to operate Mitsubishi Power Aero’s FT4000, a gas turbine unit that is a land-based variant of Pratt & Whitney’s PW4000 turbofan aircraft engine.

That fuel test will complement a Pratt & Whitney-led Department of Energy project known as the Hydrogen Steam Injected Intercooled Turbine Engine, or HySIITE. That engine is expected to achieve zero in-flight CO2 emissions while reducing nitrogen oxide emissions by up to 80% and fuel consumption by up to 35%, mostly thorough its use of cryogenic hydrogen combustion and the recovery of water vapor.

The project's use of water vapor is particularly novel in aviation, Webb said. The engine would capture vapor and run it through a heat exchanger, using it to do things like create steam, generate electrical power, control the hydrogen flame and reduce its nitrogen oxide emissions. The technique itself "has been known for a number of years, but our people have figured out how to make a flying version of it," Webb said.

"This is our brainchild," he said. "We have a group of highly talented people who do nothing but think of how to do things more efficiently."

Separately, the company will work with the University of Connecticut School of Engineering on another Department of Energy project that focuses on the use of ammonia – which is composed mostly of hydrogen – as a zero-carbon fuel for power-generating turbines. 

History shows hydrogen can be viable as fuel – Pratt & Whitney, for example, built an engine that ran on hydrogen in the 1950s. But there are obstacles to overcome, and they start with airframe design. Hydrogen's low energy density means it is commonly compressed for use as fuel and stored in large, heavy tanks – meaning it probably can't be stored in the wings, as jet fuel is.

While that’s a challenge, it wouldn’t be the first time a new type of engine drove design changes, Webb said. And with projects such as HySIITE, the efficiencies could offset any design penalties associated with hydrogen-powered engines and make the fuel more economically enticing for operators.

"We’ve always been a company where we first think: 'What's the right engine for the market?' and airplane makers will build their airframe around that," he said.

Making hydrogen work as aircraft fuel will require collaboration between airframers and propulsion providers, and, much like SAF, it will require new infrastructure efforts by energy companies and governments around the world.

Plane flying over a field of grass

"Our engineers are hard at work developing technologies to enable a greener future for the aviation industry. That includes engines that can burn clean alternate fuels such as sustainable aviation fuels and hydrogen, leading to reduced fuel consumption and emissions."

Juan de Bedout | Vice President | Aerospace Technologies

Lighter, more efficient systems

The more weight you can keep off an aircraft, the more efficiently that aircraft will use fuel. To that end, Raytheon Technologies’ aviation businesses are working to make their components and systems lighter while maintaining high standards of safety.

This effort includes essentially every part of the plane, from the nacelles that house the engines to the seats inside the cabin.

"That's a huge focus for us," said Ridgeway, pointing to Collins Aerospace's work to reduce weight and power consumption in areas including interior lighting, galleys and lavatories.

Advanced materials such as composites are helping build lighter parts, as are advanced manufacturing processes including additive manufacturing and tomo-lithographic molding, where complex structures are made from powdered metals, ceramics and polymers.

Digital design techniques are also helping. One example, Ridgeway said, are the doors for large commercial aircraft. While they seem simple on the surface, they're packed with intricate parts like hydraulics, levers and the mechanisms that store and activate the safety slide.

Historically, those systems and their many components have been designed and manufactured separately. Designers at Collins Aerospace are now using digital engineering and advanced manufacturing techniques to design them in parallel, and to make them simpler, lighter and more efficient.

And that's just for one part. When you apply that approach to the entire aircraft, Ridgeway said, that's where things get really exciting.

"In the industry as a whole, people are looking forward to the next clean-sheet aircraft that will really allow this benefit to pop up," she said.

Optimizing routes and operations

Another way to reduce an aircraft's fuel burn is to put it on the most efficient flight path possible. Through better use of the real-time data flowing through the aviation ecosystem, air traffic controllers can help pilots follow near-optimal routes, altitudes and speeds during each phase of flight.

That optimization, generally referred to as trajectory-based operations, "is a pretty large part of our getting-to-net-zero plan," Ridgeway said.

Collins Aerospace has been upgrading avionics so navigation systems can harness information to better plan trajectory, flight paths and other factors for more efficient operations. And Raytheon Intelligence & Space, also a Raytheon Technologies business, has been fielding and upgrading state-of-the-art air traffic management systems as part of the U.S. Federal Aviation Administration's Next Generation Air Transportation System portfolio. Those systems are delivering trajectory-based operations capabilities and enabling controllers to manage air traffic more efficiently.

There are also opportunities to reduce fuel consumption through improved taxi and ramp operations. That would require more intelligence in the aircraft avionics, new automation in air traffic management systems, advanced air-to-ground datalink communications, more accurate and timely weather information, as well as improved systems and capabilities at airlines’ operations centers.

Collectively, Collins Aerospace and Raytheon Intelligence & Space have been providing and modernizing datalink and enterprise network solutions to support airlines and the FAA. They have also been key players in providing weather information capabilities including sensors and integrated processing systems. Together, operational improvements could lead to reductions in aircraft CO2 emissions by up to 10%.

The targets for sustainable aviation are ambitious, and the measures required to achieve them are many. But the broad expertise of the aviation experts across Raytheon Technologies puts the company in a prime position to invest in key capabilities and deliver on many fronts, Ridgeway said.

"There's no single path to net-zero. It's going to take multiple approaches, tailored to different markets and platforms throughout the industry," Ridgeway said. "That's why we're collaborating across our company, investing in R&D to support airframers and airlines with a portfolio of products to help reach the goal."