Continuous Lower Energy, Emissions, and Noise (CLEEN) Program

The Continuous Lower Energy, Emissions and Noise (CLEEN) Program is the FAA's principal environmental effort to accelerate the development of new aircraft and engine technologies that will reduce noise, emissions, and fuel burn. Through the CLEEN Program, the FAA partners with the aviation industry via a cost-sharing approach to enable the industry to expedite integration of these environmentally beneficial technologies into current and future aircraft. Technologies developed by the CLEEN Program will result in a fleet of aircraft that produce less noise, fewer emissions, and use less fuel.  These technologies support the overall environmental performance goals of the FAA’s Next Generation Air Transportation System (NextGen) to achieve environmental protection that allows sustained aviation growth.

The FAA announced CLEEN Phase III awardees on September 10, 2021.


Through the public-private partnership of the CLEEN Program, the FAA and industry are working together to develop technologies that will enable manufacturers to create aircraft and engines with less noise, fewer emissions, and improved fuel efficiency. The technologies being accelerated by the CLEEN Program have relatively large technological risk but also enhanced benefits. Government resources help mitigate this risk and incentivize aviation manufacturers to invest in and develop these high reward technologies which might otherwise not be pursued. By cost-sharing the development with the FAA, industry is willing to accept the greater risk and can better support a business case for these technological developments. Once these risks are addressed and the technology is matured via the CLEEN Program, the companies apply these technologies to their future aircraft and engine products, leading to noise, fuel burn, and emissions benefits throughout the fleet for years to come. In addition to these benefits, the CLEEN Program has resulted in better analysis and design tools that improve the aircraft or engine products produced by these companies, well beyond the benefits provided by individual technology applications.

The CLEEN Program is implemented in five-year phases, and has goals for noise, fuel burn, and emissions. In 2010 the FAA initiated the first phase, entering into five-year agreements with Boeing, General Electric (GE), Honeywell, Pratt & Whitney (P&W), and Rolls-Royce.  

In those five years, technologies were matured and demonstrated in major ground and flight test demonstrations, paving the way for introduction in future aircraft. Since then, a number of these technologies have successfully transitioned into new aircraft and engines that are flying today.

Based on the success of this program, the second phase of CLEEN was initiated in 2015 for a five-year term. Under the CLEEN Phase II program, FAA awarded five-year agreements to Aurora Flight Sciences, Boeing, Collins Aerospace, America's Phenix/Delta TechOps/MDS Coating Technologies, General Electric, Honeywell, Pratt & Whitney, and Rolls-Royce. 

To receive funding from CLEEN, industry partners need to match or exceed the funds provided by the FAA. Through the first two phases of CLEEN, industry has contributed $388 million of cost share to the CLEEN Program, which has exceeded the FAA contribution of $225 million.

Following subsequent successes under the second phase, the third phase of the CLEEN Program was launched in 2021 with research and development activities planned to run through 2026.

A fourth phase of the program is in development, planned to run 2025 through 2029. A market survey for CLEEN Phase IV was released in December 2022. A solicitation for proposals is expected to be released in 2024. 

Program Goals

All three phases of the CLEEN Program have targeted reductions in aviation noise, emissions, and fuel burn. 

The CLEEN Phase I and II Program goals include developing and demonstrating:

  • Certifiable aircraft technology that reduces aircraft fuel burn, and/or supports the FAA's goal to achieve a net reduction in climate impacts from aviation;
  • Certifiable engine technology that reduces landing and takeoff cycle (LTO) nitrogen oxide (NOx) emissions below International Civil Aviation Organization (ICAO) Committee for Aviation Environmental Protection (CAEP) standards, and/or reduces absolute NOx production over the aircraft's mission;
  • Certifiable aircraft technology that reduces noise levels, relative to the Stage 4/5 standards and/or reduces the noise contour area in absolute terms; and
  • "Drop-in" sustainable aviation fuels, including quantification of benefits. Drop-in fuels will require no modifications to aircraft or fuel supply infrastructure.

As industry meets the program's goals, the FAA has made the goals for successive phases of the program increasingly more stringent. Further, additional goals have also been added over time. In addition to the above goals, CLEEN Phase III goals include developing and demonstrating certifiable aircraft technology that:

  • Reduces community noise exposure;
  • Reduces non-volatile particulate matter emissions relative to the CAEP/11 standard; and
  • Reduces noise levels during the LTO cycle for civil supersonic airplanes and/or reduces absolute NOx emissions for civil supersonic airplanes over the aircraft's mission.
Quantitative goals for subsonic fuel burn, emissions, and noise reductions under CLEEN Phases I, II, and III
Goal Area CLEEN Phase I CLEEN Phase II CLEEN Phase III
Noise Reduction Goal 25 dB cumulative noise reduction cumulative to Stage 5 25 dB cumulative noise reduction relative to Stage 5 and/or reduces community noise exposure
Fuel Burn Goal 33% reduction (relative to year 2000 best-in-class in-service aircraft) 40% reduction (relative to year 2000 best-in-class in-service aircraft) 20% below CAEP/10 CO2 standard
NOx Emissions Reduction Goal 60% margin to CAEP/6 landing/take-off NOx emissions standard 70% margin to CAEP/8 landing/take-off NOx emissions standard
Non - volatile Particulate Matter Emissions Reduction Goal Reduction relative to CAEP/11 standard
Entry into Service Target 2018 2026 2031

Fuels Activities

In addition to the aircraft technology development work under CLEEN, phases I and II of the program have supported fuel properties and performance testing and demonstrations. This testing facilitates new sustainable aviation fuel (SAF) approvals by standard setting organization ASTM International. For more information on the full scope of FAA's SAF activities, please see the Sustainable Aviation Fuels site.

The third phase of the CLEEN Program is focused on gathering test data to support the certification and qualification of greater than 50% blends of SAF with traditional petroleum-based jet fuels. This includes testing fuels with varying chemical compositions to determine compositional effects on seal performance, a current barrier to higher SAF blend volumes. Testing also includes combustor performance evaluations of synthetic aviation turbine fuels currently in the ASTM D4054 evaluation process, including fuels with unique chemical compositions such as a highly cycloparaffinic fuels.

The CLEEN Program is interested in fuels that are drop-in compatible with the existing pipeline and airport fueling infrastructure but have changes in their composition that could help an aircraft meet the CLEEN Program goals.

Technology Assessment Activities

In addition to the technology and fuel development activities described above, CLEEN conducts independent technology modeling and benefits assessments. This work is conducted under the Aviation Sustainability Center of Excellence (ASCENT) to model and assess aircraft technology for CLEEN Phase II (ASCENT Project 37).

According to analysis done by Georgia Tech in 2021, the technologies matured in the first five year phase of CLEEN will reduce U.S. fleet-wide fuel burn by 1.4 percent by 2030 and 2.6 percent by 2050, providing a cumulative savings of 9.3 billion gallons of jet fuel. The CO2 savings from reduced fuel burn are the equivalent of taking 781 thousand cars from the road from 2020 to 2050. In addition to saving airlines 18.7 billion dollars on fuel, technologies from the first phase of CLEEN will contribute to a 14% decrease in the land area exposed to significant noise, as defined by a day-night noise level (DNL) of 65 dB. 

CLEEN Phase II technologies are expected to enter operational service by 2026, providing further benefits to fuel burn, emissions, and noise. An ongoing assessment of CLEEN Phase II’s projected fleet-wide benefits has estimated that the program will reduce fuel consumption 2.4 percent by 2030 and 8.8 percent by 2050, bringing the contribution of CLEEN Phase I and II to 11.5 percent fuel burn reduction in the fleet by 2050.8 

Cumulatively, CLEEN Phases I and II are estimated to reduce consumption of fuel by 34.7 billion gallons by 2050, saving airlines $69.5 billion (based upon 2021 price of $2/gallon, with no inflation adjustment), and reducing CO2 emissions by 404 million metric tons. These CO2 reductions are equivalent to removing 2.9 million cars from the road from 2020 to 2050.

Consortium Meetings

The CLEEN program holds biannual consortium meetings occurring in May and November of each year. During the meeting companies provide detailed descriptions of the progress of their technology development projects. While the majority of the meeting consists of government-only review sessions, the meeting also includes one open day where companies share highlights of their work with the general public. Please contact for more information.

The next CLEEN Consortium Meeting is planned to be held November 6-9, 2023 in Indianapolis, Indiana. 

If you are interested in attending, please contact us at

CLEEN Reports & Meetings

CLEEN Phase I Final Reports

CLEEN Phase II Final Reports

CLEEN Phase III Final Reports

CLEEN Phase III Consortium Meetings

Last updated: Monday, April 08, 2024