Aircraft noise is the undesired sounds that arise, primarily when planes start and land. At start-up the engine thrust is high but because the plane usually climbs steeply, a relatively limited geographic area is subjected to noise. In approach the motor thrust is considerably lower, but the geographic area that is affected is larger as the plane is in a glide path in toward the runway, which is necessary with respect to flight safety.

Dr. Ian Waitz's group in aeronautics and astronautics has come up with an idea that could significantly reduce the noise from jet engines by injecting air from the trailing edges of the rotating blades within the engine.To aircraft manufacturers and operators, noise is a problem as serious as emissions. 'It significantly impacts the economics,' said Dr. Waitz, an assistant professor and director of the Aero-Environmental Research Laboratory, which also has a program addressing emissions from aircraft engines. Noise from planes flying over residential areas impairs people's ability to work, learn in school and sleep, and consequently also results in lowered property values in affected areas. As passenger volume increases and new and larger airports are built, noise is becoming even more of a concern.

In 2001, the ICAO Assembly endorsed the concept of a 'balanced approach' to aircraft noise management (Appendix C of Assembly Resolution A35-5 (pdf)). The Assembly in 2007, reaffirmed the 'balanced approach' principle and called upon States to recognize ICAO’s role in dealing with the problems of aircraft noise (Appendix C of Assembly Resolution A36-22 (pdf)). This consists of identifying the noise problem at an airport and then analysing the various measures available to reduce noise through the exploration of four principal elements, namely reduction at source (quieter aircraft), land-use planning and management, noise abatement operational procedures and operating restrictions, with the goal of addressing the noise problem in the most cost-effective manner. ICAO has developed policies on each of these elements, as well as on noise charges. The recommended practices for balanced approach are contained in Doc 9829 – Guidance on the balanced approach to aircraft noise management.