Chapter 6—Discussion


Index 1 2 3 4 5 6 7 References App A App B App C

The use of the ‘new’ noise indicators described in the earlier Chapters has generated much discussion on some of the broader concepts underlying the conventional approaches to aircraft noise information. These are explored in the following Sections.

6.1 Rethinking the concept of ‘acceptable’—Enabling the individual to decide on ‘acceptability’

A common reaction when a person is first presented with the noise indicators shown in this paper is for them to ask what is the ‘acceptable’ number of jet aircraft movements and/or number of events louder than 70 dB(A) on an average day.

This suggests that the person is trying to translate the information into an ANEF type approach where on one side of a line the noise is considered ‘acceptable’ and on the other side ‘unacceptable’. It is considered that it would be helpful if we could now move beyond this ‘black and white’ approach.

The underlying basis of the ANEF is that it will predict the level of community reaction to a certain level of noise dose. While this type of information is useful for establishing broad acceptability standards (e.g. the land use acceptability advice in AS2021) it does not help the individual to gain an understanding of how noise will affect them. This dilemma was shown in the discussion in Section 1.2—in most circumstances a person wants to know how the noise will impact on him or her not what proportion of the total population will consider themselves affected.

This issue was picked up in the Senate Select Committee Report ‘The ANEF system…did not provide people potentially exposed to aircraft noise with sufficient information to enable them to judge on a rational basis how they [as individuals] might be affected and hence whether the predicted level of noise would be acceptable to the’ [ref 19].

Experience at Sydney which has led to the development of the indicators described in this paper has clearly demonstrated that aircraft noise can be described in non technical terms to give individuals enough information to allow them to make up their own mind whether the noise is likely to affect them or be ‘acceptable’ to them.

If a person is told where the flight paths are how many movements there are at what time of day what the bad days will be like etc it enables the person to form a mental image of what the noise will be like (cf the type of information given to the public cited in Section 1.2). Armed with this information the person is then able for example to make an informed decision about going to live in a certain area or to decide whether to object to a proposed development at an airport.

Noise indicators based on the type of information which enables a person to form a mental image of the noise may be termed ‘relational’ indices. That is they describe the noise in a way that the person can relate to. Ideally a relational indicator will be able to be monitored and verified by the individual without any need for special equipment or expertise. Clearly the indicators discussed in Chapters 2 and 3 are the most pure relational aircraft noise indices—they can be simply observed by a person watching aircraft. The N70 is also relational as it describes aircraft noise in the way a person perceives and talks about noise—as a series of loud noise events. However it does require the use of a sound level meter (or a computer model) to be calculated.

The ANEF falls at the other end of the spectrum and is clearly ‘non-relational’. A person does not perceive think or talk about aircraft noise by accumulating the amount of noise energy they have received over a year.

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6.2 Using information as a tool to improve compatibility between communities and airports

The strategies employed to minimise community exposure to aircraft noise can be broadly placed in two categories. Those strategies directed at reducing the amount of noise emitted over residential areas (e.g. specified flight paths curfews noise certification of aircraft etc) and those directed at protecting the receiver from the noise (e.g. land use planning controls to stop residential encroachment toward airports insulation programs etc).

The operational controls embodied in the first of these categories are the subject of ongoing development and refinement at most airports. While the strategies in this category have led to very significant reductions in the level of community aircraft noise exposure (cf the exposure levels that would otherwise have occurred) they have not eliminated the aircraft noise problem. Virtually all airports inevitably impose aircraft noise on neighbouring communities.

The ANEF system which is picked up in Australian Standard AS2021 is directed at the second category through controlling land use around airports. The acceptability criteria for residential development in Australia contained in the Standard are amongst the strictest in the world. Table 6.1 gives a comparison of the criteria for a number of countries.

Despite the efforts encompassed in this two pronged attack aircraft noise pressures at some airports are tending to increase not decrease. A particularly problematic aspect of the issue is that the majority of complaints and pressures to restrict airport operations come from persons living in areas which the ANEF system indicates are suitable for residential development—that is outside the 20 ANEF (see Figure 1.1).

Table 6.1: Comparison of Aircraft Noise Based Land Use Planning Controls

Noise Exposure ANEF Australia United States Netherlands France Canada Germany
> 40 No housing No housing No housing No new Housing Housing not Recommended No new Housing
30–40 No new housing; insulation of existing housing at Sydney No new housing; insulation of existing housing No new housing; insulation of existing housing Limited new housing Housing not Recommended Limited new housing
25–30 No new housing No restrictions No new housing No restrictions New housing with insulation Restrictions in some States
20–25 New housing with insulation No restrictions No new housing No restrictions No restrictions Restrictions in some States
< 20 No restrictions No restrictions No restrictions No restrictions No restrictions No restrictions

Many of the people raising this issue live in areas quite distant from an airport and it would clearly be impractical to prohibit residential development over massive urban areas on the grounds of aircraft noise.

Clearly there are people who consider themselves badly affected by noise at levels much lower than 20 ANEF—the level of acceptability for the siting of new housing specified in AS2021. This is not inconsistent with the findings of the NAL study which showed that at the 20 ANEF level 10% of the population considers itself ‘seriously affected’ by aircraft noise [ref 3]. Given this some airports have been advocating that land use planning restrictions on residential development be extended to the 15 ANEF. This approach may be valid in areas where there is still undeveloped land which can be protected for non noise sensitive uses such as industrial.

The counter argument to this is the fact that there are very large numbers of persons who appear to very happily live in areas exposed to aircraft noise say up to the 25 ANEF level. Therefore extending the boundaries of the controlled areas beyond the 20 ANEF would represent a very broad brush approach to a problem which only affects a section of the population. In these circumstances it is considered that there is much to be said for continuing to develop and refine targeted information tools which will enable noise sensitive people to make decisions that enable them to avoid aircraft noise.

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6.3 Targeting the noise sensitive individual

The discussion in the previous Section focuses on reducing the level of aircraft noise exposure as a way to reduce community pressures on airports. However an important strategy that is often overlooked is that of improving information flows so that the reaction to a particular level of noise is reduced.

Experience has shown that the most strident complaints often come from people who believe they have been misled in some way. They may have received advice on aircraft noise directly from the airport or an official body in the form shown in Section 1.2 or they may have independently examined the ANEF contours published by an airport. In either case they are likely to have been presented with information on future aircraft noise which led them to envisage a certain pattern of noise exposure which did not eventuate.

It is of course more likely that an aircraft noise sensitive person rather than a noise tolerant person will seek advice on noise exposure patterns or examine information published by an airport before making a house move. They are therefore likely to be particularly focussed on the message given in the information.

The generation of an ‘anti airport’ resident as a result of a perception of misleading information can arise in a number of ways. In particular from data issued during the environmental assessment process for a new project (e.g. new runways or flight path arrangements) or from advice given to a person moving into a new house which is in an area where there is existing audible aircraft noise. The circumstances surrounding the EIS for the third runway at Sydney Airport are a prime example of the first case. Many people claim that they did not object during the EIS process because the ANEF information led them to believe that they would not be affected by the project. This was an important issue raised before the Senate Inquiry [ref 6].

As discussed in Section 6.1 if a person is fully informed of aircraft noise exposure patterns in a way which they can understand using relational noise indicators (ie numbers/times of overflights etc) before making a house purchase they can factor this in to their decision making. If they then decide to proceed with the house move but armed with full information experience is that they are less likely to become an ‘anti airport activist’ if they subsequently hear aircraft noise after they have moved in to the new home.

On the other hand if the person is not informed of audible aircraft noise before the move and only becomes aware of it after moving into a new home it can evolve into a major issue for the person. This is particularly likely where they have moved into a house which is a long way from an airport. In these circumstances the person expects to receive no aircraft noise and therefore even very low levels of aircraft noise can become a significant source of annoyance.

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6.4 Using relational indicators in noise forecasts

The information in the paper has focussed on reporting historic or current aircraft movement and associated noise exposure patterns. However some interest has been shown in using relational indicators in noise forecasts to help explain the information in published ANEFs.

The use of the relational indicators has essentially been kept to current data because to date the greatest demand from the public has been for this type of information. People predominantly seek information about aircraft movements they have complained or are concerned about—which in general is in the immediate past. Alternatively they want to know what it would be like in the immediate future if they were to move into an area or if new procedures such as revised flight paths were to be introduced. The question is whether the community would be interested in knowing for example how many events there will be louder than 70 dB(A) on an average day in twenty years time.

The ANEF is a land use planning tool. Since its prime purpose is to stop long term residential encroachment on airports it has much longer time horizons than the immediate noise information generally sought by the public. For example the ANEF for Perth Airport has a fifty year horizon. Given this ANEF contours do not generally portray current or near term noise exposure patterns—they broadly reflect what the noise exposure patterns are likely to be at some time in the future when for example one or more new runways may be in operation. Therefore in many cases ANEFs are solely planning lines which even if they could be understood by the layperson have little or no relevance to current noise exposure patterns.

Unfortunately this latter point is often poorly understood and people often erroneously look at the ANEF to gain an insight into current noise exposure patterns. Given this the preferred approach is not to translate long term ANEFs into relational indicators since this would mostlikely only reinforce the current misunderstanding of ANEF information. The preferred approach is to ensure that ANEF contours are treated solely as planning lines and that separate information be produced to describe current noise exposure patterns.

Irrespective of the above there is no reason why relational indicators cannot be used for short term forecasts. For example if at an airport there were no plans to build any new runway or change airspace arrangements say within the next five years then it would be quite feasible to produce five year noise exposure forecasts if this type of information were considered useful.

Figures 6.1 and 6.2 are examples of a future notional flight path movements chart and N70 for Coolangatta Airport for a five year horizon. These can be compared with Figures 2.2 and 4.4. These are purely illustrative projections based on the current flight path arrangements and origin/destination traffic mix with the movements being assumed to grow at 3% per annum. More refined versions of these figures could be produced if an airport wished to produce a ‘forecast’ in this form.

Relational indicators can also be successfully used for near term forecasting when comparing operating scenarios in the context of an EIS at an airport (e.g. when a new runway project is being assessed) where there has been detailed modelling of flight paths and there is confidence in origin/destination traffic forecasts.

By the same token it would be very misleading to use the indicators in circumstances where such detailed flight path modelling has not taken place or there is great uncertainty in traffic forecasts.

Figure 6.1

Figure 6.2


Last Updated: 9 July, 2014