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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. Through the CLEEN Program, the FAA is a cost-sharing partner with industry. CLEEN projects develop technologies that will reduce noise, emissions, and fuel burn and enable the aviation industry to expedite integration of these technologies into current and future aircraft. CLEEN is a key element of the NextGen strategy to achieve environmental protection that allows for sustained aviation growth.

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


About CLEEN

In 2010 the FAA initiated the first CLEEN Program, entering into five-year agreements with Boeing, General Electric (GE), Honeywell, Pratt & Whitney (P&W), and Rolls-Royce. These companies matched or exceeded the FAA funding in this cost-sharing program. Over the five-year period, the FAA invested a total of $125 million. With the funding match from the five companies, the total investment value exceeded $250 million.

Building upon the success of the initial CLEEN Program, in 2015 the FAA initiated a follow-on program, CLEEN Phase II, which continues efforts to achieve the CLEEN goals and develop and demonstrate aircraft technology and alternative jet fuels.

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. These companies match or exceed the awards in this cost-sharing program. The total federal investment has been approximately $100 million over five years.

To receive funding from CLEEN, industry partners need to contribute at least 100% cost share to the program. Through the first two phases of CLEEN, industry has contributed $388 million of cost share to the CLEEN Program, which has far exceeded the FAA contribution of $225 million.

The goals of the CLEEN Program are tied to the environmental standards that aircraft and engines are required to meet as a part of airworthiness certification. As aircraft technology advances, the FAA has made the CLEEN goals increasingly more aggressive. Further, additional goals have been added in later phases of the program. In 2021, the FAA initiated CLEEN Phase III. Like the first two phases of the CLEEN Program, the third phase of CLEEN will target reductions in aircraft noise, emissions and fuel burn. In a change from prior phases, the third phase of the CLEEN Program also includes goals for community noise exposure and aircraft engine particulate matter emissions. Additionally, whereas the first two five year phases of CLEEN focused on subsonic civil transportation, CLEEN Phase III is open to technologies for both subsonic and supersonic aircraft.

Program Goals

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;
  • "Drop-in" sustainable aviation fuels, including quantification of benefits. Drop-in fuels will require no modifications to aircraft or fuel supply infrastructure.

In addition to the above goals, CLEEN Phase III goals include developing and demonstrating certifiable aircraft technology that:

  • Reduces community noise exposure;
  • Reduces 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.

CLEEN Phase III is also focused on assessment of jet fuels that could provide reductions in emissions or improvements in efficiency, including fuels that enable advancements in aircraft and engine design. This includes both conventional and alternative jet fuels.

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
Particulate Matter Emissions Reduction Goal Reduction relative to CAEP/11 standard
Entry into Service Target 2018 2026 2031

For more information on the CLEEN Program, its benefits, and accomplishments to date, please see the CLEEN Program Summary and Status Report.

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 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 also aims to advance the development and introduction of hydrocarbon jet fuels for aviation that could enable improvements in fuel efficiency and reductions in emissions. This includes fuel blends. 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 was initially done through the now complete PARTNER Center of Excellence Project 36 with the Georgia Institute of Technology. This work has continued under the Aviation Sustainability Center of Excellence (ASCENT) to model and assess aircraft technology for CLEEN Phase II (ASCENT Project 37), as well as other emerging technologies and their impacts on aircraft environmental metrics (ASCENT Project 10).

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 cleen@faa.gov for more information.

The next Consortium Meeting will be held November 1-5, 2021.

If you are interested in attending, please contact us at cleen@faa.gov.

CLEEN Reports & Meetings

Phase 1

Phase II

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