Aircraft Noise

What are the effects of aircraft overflight noise?
How is aircraft overflight noise measured?
Effect on sleep

N70 noise metric
What are the impacts on land use planning?
What are the impacts on property values?
Noise Management Measures

 

What are the Effects of Aircraft Overflight Noise?

Aircraft overflight noise can affect people in many different ways. It can, for example, make conversation difficult, disturb those watching television or listening to the radio, or interfere with other forms of communication. Aircraft noise can also result in various forms of sleep disturbance. People can also be annoyed or be frightened by aircraft overflight noise. Other effects include reduction in housing values, impacts on wildlife and reduced enjoyment of recreational and natural areas. However the noise from aircraft must be considered in an holistic sense by looking at the full perspective which includes other external noises like from highways and rail.

How is Aircraft Overflight Noise Measured?

The way the ear responds to different types of noise is usually measured by using the A-weighted decibel (dBA). Because of the way the dBA scale is calculated, a 10 dBA increase in noise is generally equivalent to doubling the loudness of the noise.

A useful way of describing aircraft noise is to use the maximum noise level of the particular aircraft as it flies overhead. This has been measured in dBA and allows an estimate to be made of the level of disturbance to sleep and communication.

Another, and more common, measure of aircraft noise exposure in Australia is the Australian Noise Exposure Forecast (ANEF) System. This system takes into account the noise level of each aircraft passing overhead, the number of movements and the time of day or night. An Australian Standard (AS 2021) has been developed based on this system and provides local authorities with guidelines for planning land uses around airports. This Standard has been updated several times,and the latest version is -2000.

The ANEF system yields a number of measures which are used for different purposes. One of these, the Australian Noise Exposure Concept (ANEC), which is based on indicative data on aircraft types, aircraft operations and flight zones, is used to provide a measure of aircraft noise impacts in an EIS. The results are exactly the same as the ANEF, but the ANEC is indicative and not certified by DoTRS.

The community-wide response to aircraft noise can sometimes be partially assessed in economic terms through an estimate of the potential reduction in property values. There are, however, other impacts that cannot be so precisely defined, such as effects on health and other social impacts on individuals and communities.

Effect on Sleep

One of the issues is whether night-time operations at an airport should be restricted by a curfew (as are operations at Sydney Airport). Using data from the Second Sydney Airport studies, this section shows how the disturbance to sleep can be studied. Table 1 summarises the potential for each airport option to disturb sleep when the airport is operating at 30 million passengers per year. The table provides an estimate of the frequency of awakenings that may occur due to average operations of the airport options. Also provided is the ‘worst case’ prediction of the number of people affected by noise events exceeding 60 dBA during the night (10.00 pm to 6.00 am). An external noise level of 60 dBA approximates an internal level of 50 dBA with windows open, which is within the range in which sleep can be disturbed.

Table 1: Disturbance to Sleep for the Airport Operating at 30 Million Passengers per Year
Noise Indicator

Population Affected1

OPTION A OPTION B OPTION C
People that may, on average, be awoken the following times:
  once a night less than 100 less than 100 less than 100 to 100
  once every 2 nights 500 to 1,000 300 to 800 400 to 600
  once every 5 nights 6,000 to 8,000 3,500 to 6,000 1,500 to 17,000
People that may experience the following number of noise events greater than 60 dBA on a worst case night:
  greater than 5 events 18,000 (4,500)2 19,000 (4,500)2 47,000 (2,000)2
  greater than 2 events 124,000 (60,000)2 108,000 (39,000)2 178,000 (48,000)2
Notes: 1: Based on population projections for 2016.
2: Figures in brackets represent impacts with the adoption of potential noise management measures.
3: There are limitations in the accuracy of predicting future populations.  Estimates of population greater than 10,000 have been rounded to the nearest 1,000; estimates of population between 1,000 and 10,000 have been rounded to the nearest 500; and estimates of population less than 1,000 have been rounded to the nearest 100.  Estimates of population less than 100 are expressed as less than 100.
4: Impacts assume all residential properties within the 35 ANEC contour would be acquired.

The figures in brackets in Table 1 and the following tables indicate the number of people that might be affected if flight paths were designed to reduce noise impacts. For example, while Option C has the potential to create the greatest disturbance to sleep, it also has the greatest potential for a reduction in impacts with the implementation of noise management measures.

N70 Noise Metric

Aircraft noise can interfere with communication such as conversation, watching television and listening to the radio. The number of noise events exceeding 70 dBA over a 24-hour period tends to indicate the degree of disruption to normal domestic communications. When outside noise levels are below 70 dBA, communication inside the home is unlikely to be disrupted, while above 70 dBA some interruption is likely. The same comment applies in regard to schools, except that the critical outside noise level is 65 dBA.

Disturbance to domestic communication was therefore measured in terms of N70 data; that is, the number of  times in an average day that a location is exposed to external aircraft noise of more than 70 dBA. N65 data were used to  assess disturbance to educational facilities.

Table 2 summarises the impacts of aircraft overflight noise from the Sydney Airport options on communications within domestic situations when the airport is operating at 30 million passengers per year. The N70 chart is shown graphically here, with the maximum extent of the N70 contours for an airport option operating at 30 million passengers per year. These contours show the outside extent of a large range of N70 levels which resulted from examining the combinations of assumptions about air traffic movements and the different ways the airport might be operated. I've got an ANEF drawing of the same airport and flights (actually its an ANEC, but there's no difference). See how the N70 ties to the ANEF 15.

Table 3 summarises the potential impacts on existing educational facilities for each Sydney airport option.

Table 2: Disturbance to Communication for the Airport Operating at 30 Million Passengers per Year
Noise Indicator

Population Affected1

OPTION A OPTION B OPTION C
People that may experience, on average, the following number of noise events over 70 dBA a day:
  greater than 100 events 400 to 900 (NR)2 300 to 700 (NR)2 300 to 500 (NR)2
  greater than 50 events 2,500 to 5,000 (1,500)2 2,000 to 4,000 (NR)2 700 to 1,000 (NR)2
  greater than 20 events 8,500 to 9,500 (5,000)2 7,000 to 9,500 (NR)2 6,000 to 17,000 (NR)2
  greater than 10 events 15,000 (10,000)2 16,000 to 17,000 (NR)2 60,000 to 72,000 (32,000)2
Notes: 1: Based on population projections for 2016.
2: Figures in brackets represent impacts with the adoption of potential noise management measures. NR means no reduction in impact.
3: There are limitations in the accuracy of predicting future populations.  Estimates of population greater than 10,000 have been rounded to the nearest 1,000; estimates of population between 1,000 and 10,000 have been rounded to the nearest 500; and estimates of population less than 1,000 have been rounded to the nearest 100.  Estimates of population less than 100 are expressed as less than 100.
4: Impacts assume all residential properties within the 35 ANEC contour would be acquired.

 

Table 3: Aircraft Overflight Noise Impacts on Existing Educations Facilities for the Airport Operating at 30 Million Passengers per Year
Noise Indicator

Education Facilities1

OPTION A OPTION B OPTION C
Educational facilities that may experience, on average, the following number of noise events over 65 dBA between 9.00 am and 3.00 pm:
  greater than 20 events 15 (5)2 13 (2)2 25 (3)2
  greater than 10 events 20 (14)2 20 (11)2 75 (26)2
Notes: 1: Definition of educational facilities includes child-care centres.
2: Figures in brackets represent impacts with the adoption of potential noise management measures.

 

What are the Impacts on Land Use Planning

The maximum extent of the ANEC contours for each of the airport options operating at 30 million passengers per year is shown in the ANEC chart graphically here. These contours show the outside extent of a large range of ANEC levels resulting from the examination of the combinations of assumptions about air traffic movements and the different ways the airport might operate. They can be compared to the N70 contours to get a feel for the inter-relationship.

Table 4 provides a summary of predicted populations impacted by ANEC levels when the airport is operating at 30 million passengers per year. It also shows the populations that might be affected if noise management measurements are adopted. In estimating likely noise reaction from these values, allowance must be made for the additional reaction to the introduction of a new noise source.

Table 4: Populations Impacted by ANEC Levels for the Airport Operating at 30 Million Passengers per Year
Noise Indicator

Population Affected1

OPTION A OPTION B OPTION C
People that may experience the following ANEC levels:
  greater than 30 200 (NR)2 less than 100 to 200 (NR)2 less than 100 to 300 (NR)2
  greater than 25 700 to 1,000 (NR)2 500 to 800 (400)2 300 to 700 (NR)2
  greater than 20 4,500 to 6,000 (2,500)2 3,500 to 5,000 (2,000)2 900 to 1,500 (NR)2
  greater than 15 11,000 to 14,000 (8,000)2 11,000 to 14,000 (7,500)2 15,000 to 19,000 (10,000)2
Notes: 1: Based on population projections for 2016.
2: Figures in brackets represent impacts with the adoption of potential noise management measures. NR means no reduction in impact.
3: There are limitations in the accuracy of predicting future populations.  Estimates of population greater than 10,000 have been rounded to the nearest 1,000; estimates of population between 1,000 and 10,000 have been rounded to the nearest 500; and estimates of population less than 1,000 have been rounded to the nearest 100.  Estimates of population less than 100 are expressed as less than 100.
4: Impacts assume all residential properties within the 35 ANEC contour would be acquired.

What are the Impacts on Property Values?

Research has shown that high levels of aircraft overflight noise can reduce residential property values in areas affected by high levels of aircraft overflight noise. For example, the potential reductions in property values resulting from the operation of the Second Sydney Airport would range from zero for residential properties within the zero to 15 ANEC band to 20 percent for residential properties in the 30 to 35 ANEC band.

The effect of aircraft noise on residential property values provided a basis for comparing the airport options. It does not provide a precise measure of possible devaluation of individual properties.

The analysis addressed only the direct impacts on dwellings in areas potentially affected by noise of greater than 15 ANEC. There is also likely to be more indirect impacts on property values such as the impacts of construction of off-airport site infrastructure and changes to land use planning controls.

Noise Management Measures

The impacts of aircraft noise from an airport could be reduced by the adoption of noise management measures. The most effective measures would be to refine flight paths and restrict some types and times of runway and flight path use to minimise overflying of residential areas, particularly at night. A noise management plan could be developed as part of the environmental management framework for the airport.

The relative performance of airport options in terms of aircraft overflight noise would vary depending on which noise indicator is examined. The implementation of noise management measures could also have varying results depending on the airport option. Consequently it is difficult to provide a definitive ranking between airport options.