FIGURE B-1 Actual and predicted exposure to significant noise (65-dB day-night average sound level) and enplanement trends for the United States, 1975-2005. SOURCE: C. Burleson, FAA, “Aviation environmental challenges,” Presentation to Panel B on December 13, 2005.

Adequately understanding and mitigating the environmental impact of aviation requires an integrated approach to noise and emissions research that considers these tradeoffs.

High-risk, long-term research is required to meet future demands. Close collaboration between government and industry is required to mature and transition promising technologies. NASA plays a critical role in supporting fundamental source noise abatement research at universities, which can lead to both revolutionary technology advances and a workforce that can answer new technical questions. Key milestones include

• Develop validated physics-based models to predict engine noise and conduct trade-off studies.

• Improve understanding and prediction capabilities, and develop propulsion cycles compatible with noise and emissions reduction.

• Develop advanced low-noise fan designs, liner concepts, and active control technologies.

• Develop concepts to reduce installed noise (e.g., adaptable chevrons).

• Develop and demonstrate propulsion designs that show the feasibility of technologies to reduce noise by 10 dB (in 15 years) from Boeing 777/GE 90 levels.

Capacity (9): In the absence of breakthroughs, increasingly strict noise requirements will constrain aviation system capacity.

Safety and Reliability (1): This Challenge will not help to achieve this objective, though equipment designed to reduce noise must be compatible with safety and reliability requirements.

Efficiency and Performance (3): Some noise reduction approaches (e.g., higher bypass ratio) increase efficiency while others (e.g., acoustic liners) increase weight, which may reduce efficiency. In addition, engines often run at nonoptimal conditions to reduce noise. Innovative noise solutions may permit new, optimized operating approaches.

Energy and the Environment (9): Aircraft noise directly impacts the environment.