The FAA is responsible for noise reduction policies. The FAA program, The Continuous Lower Energy Emissions and Noise (CLEEN) encourages the creation of aircraft noise reducing equipment. The program aims to achieve environmentally friendly goals for newer aircraft models, and also encourages the retrofitting of older aircraft.
Due to rising complaints and concerns involving loud aircraft noise, in February 2013, the International Civil Aviation Organization (ICAO) introduced a new global noise reduction standard. Chapter 14- which applies to jet and propeller driven planes- is a more stringent standard compared to the previous standard, Chapter 4. The standard applies to newly designed aircraft operating after 2017.
The ICAO introduced a set of stages to help implement the new noise reduction standard. For an aircraft to be airworthy, an aircraft manufacturer must be compliant with the stage in which their aircraft is classified into. There are four sound stages for civil aircraft, with 1 being the loudest and 4 being the quietest. To move up a category, therefore reducing noise, an aircraft can be retrofitted with noise reduction technology. Two examples of aircraft noise cancelling systems are flap side edge liners and landing gear door liners. Good time to introduce what those technologies are then transition into descriptions
Acoustic liners are essentially a buffeting system. As an aircraft comes into landing, the level of noise increases due to the engine running on full throttle during descent. This sparks complaints from surrounding civilian communities who live around the airport or under a flightpath. NASA has developed two new acoustic liner systems that can be fitted to noisier aircraft that are not part of the NextGen of aircraft.
Flap side edge liners are perforated attachments that capture the noise generated by the interrupted airflow. The surface of the flap side edge liners trap the air and channel it through various vessels. The vessels are of differing lengths, therefore forcing the sound to bounce off the channels. The flap side liners can be outfitted with a stuffing such as foam, which can be tailored to absorb the sound. In a similar design to the flap side edge liners, landing gear door liners are porous in design. The liners are constructed of numerous spaces that entrap the noise generated from the air disturbance. In an added design benefit, both the flap side edge liners and the landing gear door liners adjust the boundary conditions. In doing so, the reduction liners also reduce the amount of noise being produced.
With the introduction of the ICAO standard, noise reducing technology will become more standard. In turn, the number of people who are affected by loud aircraft noise will be reduced.
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