Methods to reduce aircraft noise pollution

Methods to reduce aircraft noise pollution

1. Control of noisier aircraft

   • Aircraft are categorised into groups according to whether they meet increasingly strict noise limits
   • Charges for noisier aircraft
   • Restricted flight times (eg. banning night flights)
   • Quota count system to encourage airports to fly quieter aircraft by restricting flight times for noisier aircraft, or by using a points system.
   • Control of supersonic flights - there are no longer any supersonic civil airliners as they are banned from almost all airports and from flying over most countries.

2. Aircraft design

   • Building aircrafts using lighter materials
     • Reduces the amount of energy needed for movement, thus reducing engine thrust and fuel consumption.
   • Blended wing aircraft
     • Engine is located in the roof so that the plane body acts as a barrier for noise pollution.
   • Aerodynamics
     • Upturned wingtips reduce air resistence.
     • Retracting or streamlining landing gear (eg. wheels and doors) help to reduce turbulence and noise pollution.
     • Having a slender and smooth wing shape to reduce drag and noise pollution from the trailing edge.
     • Welded panels create less turbulence and noise than riveted construction.

3. Aircraft operation

   • Flight paths are planned to avoid flying over high-density domestic zones and ecologically sensitive zones.
   • Fly at a constant angle (as opposed to stepped) when descending to reduce air resistence.
   • Take-off at a steeper angle to ascend to a high altitude before flying over domestic zones to reduce the noise pollution they experience.
   • Restrict the number of night flights, particularly take-offs.

4. Airport design and location

   • Location away from major population centres
   • Taxi areas away from residential areas
   • Engine test areas located away from residential areas surrounded by acoustic screens - tests should only be carried out during the day
   • Acoustic insulation on buildings affected by aircraft noise
   • Land-use restrictions near airports (eg. not allowing housing)
   • Noise deflection/absorption baffle bounds and acoustic barriers deflect/absorb noise from airports
   • Having multiple landing runways allows more time for slowing down, so wheel brake can be used which are quieter than reverse thrusters

5. Aircraft engine design

   • High bypass ratio engine
     • Has a larger fan diameter and a lower exhaust velocity, resulting in less jet noise and more thrust.
   • Chevron nozzles
     • Used on high bypass engines to make them quieter. A serrated trailed edge on the outer cowling mixes the bypass air with the surrounding air more smoothly.
   • Engine hush kits
     • Fitted to low bypass ratio engines to make them quiet.
   • Engine acoustic liners absorb noise

6. Military aircraft

   • Sensitive ecological sites (eg. seabird cliff breeding colonies), major urban areas and key industrial and medical sites are avoided
   • One can request a temporary stop to low flying (eg. for a horse show)
   • Low flying timetables may be published to the public
   • Compensation may be paid for damage caused to property or harm to livestock