An estimated 20 million people travel to and from Australia each year and over 50 million people travel on domestic flights each year.
The continued growth of the aviation sector is vital for the development of international business, trade and tourism. However, increasing aircraft movements can impact the level of aircraft noise.
How noise is made
Residents living near airports or under busy flight paths can be exposed to the impacts of aircraft noise and this can affect people in different ways. You’ve probably noticed that the level of noise you hear from a plane during take-off, landing and during flight can vary. Aircraft noise is influenced by a number of different factors, for example how far away an aircraft is and changes in engine thrust. These factors are explained in more detail below.
A moving aircraft causes air around it to be compressed, causing noise waves. Aircraft noise increases when the landing gear and flaps have been deployed, making the aircraft less aerodynamic. The large fans at the front of an engine and from the jet exhaust, as well as propellers, also cause noise waves. As air gets compressed, it reverberates against the aircraft’s surfaces and makes noise. This noise can be loudest when the aircraft is taking-off as most aircraft noise is generated by the large fans at the front of each engine and the jet exhaust.
The further away an aircraft is from the ground, the quieter it will be. Aircraft noise may become more noticeable as aircraft change engine thrust, similar to a motor vehicle accelerating, and when the flaps and landing gear are used.
Aircraft noise is also affected by humidity, air density and cloud cover. These factors can impact on how sound behaves, For example, noise waves from an aircraft can travel as far as 10km. The sound of an aircraft will also vary depending on how far away it is.
As noise waves travel, they lose energy and the higher frequency noise is absorbed by the atmosphere. This is why a more distant aircraft is often heard as a low frequency rumble, and as it approaches the pitch becomes higher.