Part 1—Principles and Approaches
- 1. Purpose
- 2. The importance of aircraft noise information
- 3. Right to know principles
- 4. Selecting the appropriate noise descriptor
- 5. Recommended approaches for responding to information requests
This guidance material is principally directed at airport operators, acoustic consultants and aviation and environmental authorities/agencies.
The broad aim of this document is to provide guidance for persons who prepare and provide aircraft noise information for use by non-experts, such as members of the public and decision-makers. For airports and aviation authorities this guidance has day-to-day application in the provision of information to the public and in routine environmental monitoring/reporting. It is also intended to be of assistance to acoustic consultants and aviation and environmental authorities in carrying out aircraft noise investigations and in preparing formal assessment reports such as Environmental Impact Statements (EISs).(1)
It is common for state and local government agencies to receive queries about aircraft noise from members of the public. In responding to these queries, these agencies generally act as secondary providers of aircraft noise information by passing on information produced by or for an airport. Until recently these agencies have typically only had access to land use planning contours and have used these as a source of aircraft noise information irrespective of the nature of the questions asked. It is intended that this guidance material will facilitate improved practices by assisting these agencies to provide the most appropriate aircraft noise advice.
In addition to assisting the providers of information, this document will assist recipients of aircraft noise information by drawing their attention to the types of aircraft noise information now available.
It is hoped that this document will generate further ideas on new ways to describe aircraft noise. This guidance material is designed to broaden thinking; it is not intended to be prescriptive.
The ultimate aim of this document is to achieve better aircraft noise outcomes for Australian airports. The purpose of this document is not to give guidance on the selection or implementation of specific aircraft noise management measures at airports. The intention is to facilitate a situation, through the presentation of a meaningful picture of the noise, which allows all parties with an interest in an airport to speak the same language and to hold open discussions on aircraft noise management strategies.
In the end, it remains the responsibility of the relevant bodies and organisations—airports, airspace management authorities, government transport and land use planning agencies and aircraft operators—to use the information and to work with local communities to implement strategies and plans which deliver acceptable aircraft noise outcomes.
There are a range of reasons why it is important that information on aircraft noise exposure is gathered and/or generated and is released in a form that describes the noise in a way that is both ‘accurate’ and comprehensible to the reader. It is important to recognise that ‘accurate’ in this context means much more than pure technical accuracy. In the context of this document it means accurate in the sense that the information gives a ‘picture’ of the noise exposure patterns around an airport which the user believes gives a portrayal of what is actually happening.
The following are key reasons why airports and aviation authorities need to allocate resources to generating and disseminating aircraft noise information.
Good environmental management practice
Environmental monitoring and reporting underpin responsible environmental management. It is now generally accepted that the pollution levels generated by any significant activity in society should be monitored and be published so that the public can be aware of the potential adverse effects which may be generated by that activity. Aircraft noise pollution is a significant unwanted by-product of aviation activities at many airports. As such, there is an onus on the aviation industry to monitor and report on these activities.
It is important that the results of environmental monitoring are archived so that long-term trends in pollution levels can be checked and published. For example, the information is vital for the preparation of accurate and comprehensive ‘State of the Environment’ reports. On a more detailed level, the information can demonstrate the changing nature of aircraft noise exposure around an airport—the gains in terms of significantly quieter aircraft; the losses in terms of increasing numbers of aircraft movements.
The gathering of this information is also essential so that when there is a proposal which will significantly change aircraft noise exposure patterns at an airport—for example, the construction of a new runway—well-established baseline data is available to permit an effective assessment of the impacts of the proposed project.
The responsibility to meaningfully respond to complaints
There is an onus on the aviation industry to be open and to be able to provide meaningful responses to legitimate questions raised by members of the public. If an airport is to effectively respond to complaints made by the public it is fundamental that ways of describing aircraft noise be used which the non-expert can easily understand and have confidence in.
In particular, the issue for many complainants is non-compliance with specific rules and regulations. Trust between the parties is dependent on all the parties being aware of the rules, knowing adherence to them is checked and being able to fully understand what is stated in compliance monitoring reports.
Disclosure—avoidance of false expectations
Experience has shown that the most aggrieved members of the public are often those whose expectations about the aircraft noise environment in the vicinity of their home have not been met. Even relatively low levels of aircraft noise have the potential to be highly annoying to a person given information which has generated an expectation of there being no aircraft noise at their home. This potential is heightened if expectations have been created by ‘official’ aircraft noise information published by or for an airport.
Similarly, it is not uncommon for a person moving into a new area adjacent to flight paths to have not given any consideration to aircraft noise. They then become very surprised when they hear aircraft noise. These people often have an implicit, rather than explicit, expectation about aircraft noise. In these circumstances the question often is “why wasn't I told?” The annoyance outcome can be essentially the same in both cases.
It is fundamental that airports need to produce, and make widely available, accurate and comprehensible information on their noise exposure patterns to allow, for example, prospective house buyers to make informed purchase decisions.
When this information strategy is in place it leads to a win/win situation. Noise sensitive residents are less likely to purchase houses under or close to flight paths so there is likely to be less community pressure on airports to restrict or modify operations.
Presenting an ‘accurate’ picture in Environmental Impact Statements (EISs)
The prime purpose of a formal environmental assessment report, such as an EIS, is to ensure that the environmental impacts of a proposal are fully examined and that the decision-maker is fully aware of the outcomes that will occur if the proposal proceeds.
Decision-makers on major airport or airspace projects are rarely aircraft noise experts and, if a fully informed decision is to be made, the aircraft noise information needs to be presented in a way that can be understood by the layperson. Providing comprehensible information in EISs takes the process beyond one which relies on the decision-maker simply having to rely on the advice of the ‘expert’.
In a similar vein, if EIS processes are to be transparent, members of the public who may be affected by a proposal need to understand the likely outcomes if the proposal proceeds. Many members of the public use EISs as their prime source of information on the likely future noise exposure patterns generated by a project at an airport, for example, the construction of a new runway. It is now considered essential that an EIS no longer be treated purely as a technical document conveying information between the noise experts representing the parties involved. It is both a technical and an information document. It is envisaged that in future the aircraft noise requirements in the terms of reference for Commonwealth EISs will fully reflect this dual role.
Providing advice to planners/prospective developers to place ANEF contours in context
Aircraft noise is normally only one of a range of issues that land use planners need to take into account when assessing a development application. Given the training and background of most land use planners it is not reasonable to expect them to be experts in aircraft noise matters.
The Australian Noise Exposure Forecast (ANEF) land use compatibility advice states that areas outside the 20 ANEF are ‘acceptable’ for any development. Since the only aircraft noise information generally presented to planners has been a set of ANEF contours, with the 20 ANEF contour being the outer one, it has probably not been unreasonable for planners in the past to have treated areas outside the 20 ANEF as being free of aircraft noise. However, it is now generally recognised that basing planning decisions solely on ANEF contours, without reference to other information (particularly on the location of flight paths), is likely to lead to less than optimal outcomes. For example, if there is a proposal to site a school in an area with an aircraft noise exposure of 19 ANEF it would be prudent, if the proposed school site is under a major flight path, to look for alternative locations. At the very least, even if there were no available alternative school sites, the designers of the building would be able to take into account the existence of the flight path.
The above points are intended to give a generic picture of the importance of producing aircraft noise information. Clearly, the extent to which resources need to be allocated in practice to the production of aircraft noise information will vary from airport to airport and depend on differing circumstances. The noise information requirements at a small airport that is distant from any population centre are naturally likely to be minimal compared to a capital city jet airport surrounded by residential areas.
It is recognised that the ability of an airport to provide aircraft noise information depends very heavily on its access to the necessary monitoring data. Most Australian airports do not have a Noise and Flight Path Monitoring System (NFPMS) and therefore it is often not practical to gather all the desired information. The NFPMSs at the major Australian airports are operated by Airservices Australia and the ability for third parties such as the airports and consultants to produce and disseminate aircraft noise information is dependent on their ability to access the underpinning data.
Polluters have a responsibility to monitor and report on the pollution they are generating and the public has a right to know environmental pollution levels. It is self evident that if pollution levels are reported in a manner that is unintelligible to the non-expert there has not been effective disclosure of what is happening.
Our experience in recent years has shown that if a meaningful picture is to be painted of aircraft noise exposure patterns around an airport a person needs, at the least, to have access to the following information:
- where the flight paths are;
- at what times aircraft use a flight path (in particular sensitive times—night/early morning, evenings and weekends);
- how often aircraft use the flight path;
- variations in activity levels from hour to hour, day to day, week to week, etc; and
- noise levels from individual flights.
It is considered best practice that every citizen has a ‘right to know’ this information if they so wish.
It is important that this information be made available in a disaggregated form and that, as far as possible, it be left unadjusted. That is, the detail should not be buried in an average day noise contour nor should information on what happens at sensitive times be hidden by the use of weightings. It is also important that the information cover areas which extend far beyond the 20 ANEF contour.
Consistent with earlier comments it would be expected that the ‘right to know’ principles would be applied on a common-sense basis. Detailed day-to-day monitoring information is not available for small Australian airports without a NFPMS and it may be that in most circumstances there will be little need for these airports to allocate significant resources to produce aircraft noise information. As a general rule, it would not be unreasonable to expect that the resources allocated to producing aircraft noise information at an airport would be directly related to the extent to which aircraft overfly noise sensitive sites around the airport and/or the extent to which the airport wishes to influence land use planning decisions in the vicinity of its boundaries or its flight paths. This issue is further discussed in Section 16.
Aircraft noise can be, and is, described in many ways. It is vital that when using an aircraft noise descriptor it is selected so that it matches the needs of the issue being examined. In the past this match has not been achieved effectively and this has contributed significantly to the expert and non-expert failing to reach a common understanding about aircraft noise exposure patterns around airports.
For the purpose of this document aircraft noise descriptors can be put in three broad categories: aircraft noise information; land use planning contours; and technical descriptors. These categories are defined solely for the purpose of establishing a definition of aircraft noise information in the context of this document. However, it is important to recognise in practice there may be, and indeed in many circumstances it is desirable that there is, an overlap between the categories. For example, when considering land use planning around an airport, it is now considered best practice that planners and decision-makers take into account both the land use planning contours which define statutory building eligibility areas and aircraft noise information. The information in this context is likely to relate to the location of flight paths and the levels of aircraft activity on those flight paths, for areas which extend beyond the contours. As indicated in Section 2, in the absence of consideration of flight path information for areas outside the contours, noise sensitive developments may be placed in areas of high overflight activity without alternative sites being examined. Therefore overlaying aircraft noise information on land use planning contours provides a more holistic approach to land use planning around an airport.
This category relates to information provided to an individual, for example a member of the public or a decision-maker, to help them understand what the aircraft noise exposure patterns around an airport are, or may be, like.
Experience has shown that non-experts do not want aircraft noise described in technical terms but want information based on ‘everyday talk’—they want the noise described in terms of where the aircraft fly, how often, at what time, etc. When aircraft noise is described in this way a person is able to draw a good mental picture of what the exposure patterns are like. This then empowers them to use their own judgement about aircraft noise in making decisions, such as whether or not to buy a house, rather than having to rely on ‘official’ advice about the ‘significance’ or ‘effect’ of noise at a particular location.
For the purposes of this document this type of information based on ‘everyday talk’ is termed transparent aircraft noise information. Transparent aircraft noise information is the focus of this guidance material. This type of information has been shown to be particularly suited to the uses identified in Section 2. Examples of this type of information are shown and discussed in Part 2.
Land use planning noise contours, known as Australian Noise Exposure Forecast (ANEF) contours in Australia, are designed as a tool to stop airports being ‘built-out’ by noise sensitive land uses.(2) They are prepared to provide guidance to land use planning authorities charged with the responsibility for making decisions on proposed land use developments in the vicinity of airports.
These contours define acceptable areas for the construction of different types of buildings around airports with the aim of achieving land uses compatible with the future aircraft noise.
These contours are generally drawn for years which are far into the future, for example in Australia at some airports up to 50 years in the future. In order to enable prudent land use planning, these distant contours often make allowance for a number of runway options, not all of which will be built, to keep open the choice of the location of the new runway(s) for some time into the future. Therefore, these contours do not normally show a picture of current or near-term noise exposure patterns around an airport. Experience has shown these contours, which are based on logarithmically averaged ‘annual average day’ aircraft noise energy, do not portray noise in a way that the non-expert can readily relate to.
Given the above, land use planning contours such as ANEFs are not considered suitable for use as an aircraft noise information tool.
There are numerous technical aircraft noise descriptors which have specialist uses. These are generally used in Australia by acoustic experts who are examining particular ‘micro’ aspects of aircraft noise exposure or are preparing the technical parts of formal environmental assessment reports such as EISs. For example, terms such as Leq (equivalent continuous noise level), DNL (day-night noise level), SEL (sound exposure level), EPNL (effective perceived noise level), TA (time above), and many other similar descriptors, are commonly found in technical reports on aircraft noise. In addition, the ANEF has conventionally been used in Australia as the main technical descriptor for carrying out detailed noise assessments in formal environmental assessment reports.
In a similar manner to the ANEF, several of the technical descriptors—such as the Leq and DNL—are commonly used overseas to draw ‘macro’ noise contours around airports for defining boundaries for land use planning and acoustic insulation eligibility. As such these descriptors can be considered to fall into two rather than one of the noise descriptor categories.
The technical descriptors referred to in this sub-section generally have one thing in common—they do not portray noise exposure patterns in a way that a layperson can relate to or can readily understand. They also cannot generally be measured or computed without specialist equipment or knowledge. Accordingly, they are not considered suitable as tools for providing aircraft noise information to the non-expert.
Given this, and consistent with the comments in Section 2, it is important to be aware that the focus on technical descriptors in formal environmental assessment reports such as EISs now needs to change and to be balanced with aircraft noise information. An EIS that does not provide the decision-makers with a clear picture of the likely outcomes of a proposal, such as an EIS that relies solely on technical descriptors, would fall short of its purpose.
Some confusion has arisen between the use of TA, the amount of Time Above a certain threshold noise level which is commonly 70 dB(A), and the use of NA, the Number of aircraft noise events louder than a certain threshold noise level which is commonly 70 dB(A). It is important that these descriptors not be used interchangeably. TA is a useful tool for looking at ‘micro’ situations, for example, where a change in procedures may increase or decrease the length of noise events over a particular location. However, experience has shown that ‘macro’ whole of airport TA contours do not describe noise in a way that relates to a person's experience and can therefore be highly misleading. A person does not normally gauge the amount of aircraft noise exposure by adding up the number of seconds from each overflight which are ‘loud’ but rather in terms of the number of overflights. For example, a layperson would not expect a great deal of noise if they were told they would receive say five minutes of noise a day above 70 dB(A). On the other hand, if the same noise exposure were expressed as 150 events a day louder than 70dB(A) they would be likely to have very different expectations. Feedback from community representatives is that the N70 gives the much more realistic picture of aircraft noise. Given this, the production and publication of ‘whole of airport’ TA contours for aircraft noise information purposes is not recommended.
These recommendations encapsulate the key lessons learnt from responding to requests for aircraft noise information from members of the public in recent years.
These suggested approaches evolved in circumstances where there was widespread community mistrust of ‘official’ aircraft noise information and where there was a critical need to re-build bridges between aviation authorities and the public.
Several of these suggestions run counter to what was standard practice up until about five years ago. However, since they have been adopted, these approaches have received supportive feedback and have led to positive outcomes for all parties.
Provide facts—let the individual make up their own mind.
- Provide transparent information and then let the recipient form their own opinion of whether the noise is likely to affect them.
- Avoid making judgements on whether a person will or will not feel affected by a certain amount of aircraft noise.
Try to provide the information the enquirer wants.
- Don't make judgements about the relevance of the information.
Be aware of the limitations of your data.
- Advise the enquirer about any significant limitations of the data you are providing.
- Take a balanced approach and try to avoid using fears of accuracy as an excuse for not providing data.
Provide information that describes the noise in a way the enquirer can relate to.
- Before giving out information ask yourself the question ‘Am I answering the question using the same language/terminology that the enquirer used when they asked it?’
Give the enquirer the type of information which relates to the question.
- For example, don't give average day information if the question relates to a specific time period.
Attempt to provide information in a form which the enquirer can independently verify.
Don't provide noise contours without also giving out information on the flight paths underlying the contours.
Be prepared to provide detailed technical advice on aircraft operations or on aircraft noise if this is what the enquirer is seeking.
- If you are not equipped to provide this material have well-established contacts and procedures so that the enquirer is able to obtain the information without being given the ‘run around’.
Don't be afraid to point out the facts to the enquirer if their perception does not accord with what has actually happened.
- Do not question their opinion on the extent to which they might consider themselves subjectively affected.
Avoid comparing aircraft noise with other noise sources such as road traffic.
- While the sound pressure level of an aircraft overflight may be the same as a car passing down a road, using this as an argument for justifying aircraft noise is likely to generate a negative reaction; treat aircraft noise as a separate issue.
Clearly differentiate between current and future noise.
- Make sure that the information provided to an enquirer relates to the time horizon that they are interested in. If a person asks for information on what the noise is like now don't use forecast information. Be careful about making promises on what may happen in the future; in particular, avoid generating unrealistic expectations about future reductions in noise exposure levels.
Until recent years aircraft noise information in Australia has essentially been based on a regime that gave ‘interpretation’ rather than ‘facts’. If a person made an inquiry about aircraft noise they were often provided with the value of the ANEF exposure level at their house. This was accompanied by an interpretation of what this meant by reference to a published land use compatibility table or to the dose/response information which underpins the table. For example, areas with an aircraft noise exposure of less than 20 ANEF have conventionally been treated as having ‘acceptable’ levels of noise.
However, this interpretation of noise impacts was based on studies examining community rather than individual reaction. Therefore, due to the wide range in individual reactions to aircraft noise, this approach inevitably led to certain people believing they had been misled by ‘official’ information.
Consistent with the advice earlier in this document, experience has shown that the potential for a person being misled is much reduced if the person is provided with ‘facts’ while avoiding ‘interpretation’. In this context ‘facts’ means information in the form of flight path location, numbers and times of movements, etc—that is, transparent aircraft noise information. Once a person is equipped with the facts they can generally make an informed assessment for themselves of whether they will find the noise at a particular location ‘acceptable’. For example this approach empowers the individual to factor aircraft noise into a house purchase decision rather than putting them in a position where they have to accept an ‘official’ judgement on the effects of the noise.
In a similar vein, the use of transparent noise descriptors in an EIS document allows an individual to form their own view on whether they are likely to find the noise exposure levels from a proposed project (such as the operation of a new runway at an airport) ‘acceptable’. If they believe this will not be the case they are empowered to make a meaningful formal submission into the process and have their views considered by the decision-maker.
In order to ensure transparency, it is important that strong efforts be made to provide the information that is being sought by a member of the public. Any indication that the information being sought is ‘irrelevant’ is only likely to lead to accusations of a ‘cover up’.
Naturally, there must be a limit to the resources allocated in responding to requests and it will not always be possible to gather some data at acceptable levels of accuracy. However, experience has shown that a request which may appear convoluted, complex or excessive may be so because the enquirer is not sure of what to ask for or what is available. With discussion, it may be that the information can be more readily provided in a different but acceptable form.
It is fundamental that when providing data to the public every effort should be made to ensure its accuracy. However, it is equally important that a balance be struck in this area and recognition be given to the fact that ‘accuracy’ cannot be considered in isolation.
If data is 100% accurate but incomprehensible to the user then, despite the accuracy, it is likely to be misleading. Similarly, data may be accurate but if it is incomplete, for example it only provides information on aircraft noise very close to an airport, it is also likely to be misleading.
In practice, data is unlikely to ever be perfect and will nearly always have some form of minor deficiency or be based on certain assumptions. It is important that these ‘imperfections’ not be used as an excuse for withholding information. The preferred approach is to recognise the shortcomings in the data and to indicate to the recipient the level of confidence that may be placed on the information.
Trust between an airport and its community can only be established if people have confidence in the truth of what they are being told. One of the best ways to achieve this is to, as far as possible, provide information in a form that can be readily verified by an individual without the need to have specialised expertise or equipment. Aircraft noise information based on numbers and times of movements, location of flight paths, etc can be readily verified. For example, it is not uncommon for a person to keep a log of the time each aircraft passes near their home—this information can be cross checked to ascertain whether it agrees with the ‘official’ published data. On the other hand, complex noise metrics generated by computer models, even if understood, cannot be easily verified by a member of the public.
Until recent years, airports had no ‘macro’ information about aircraft noise exposure over surrounding communities other than ANEF contours. These contours (whether forecasts or historic contours) are based on the ‘annual average day’. However, most requests about aircraft noise exposure patterns relate to shorter time periods such as the last two months, or to specific sensitive time slots such as Sunday mornings. Therefore, in the absence of specific information, there was a natural disconnect between the issues being raised by community members and the information being provided by the aviation authorities. As a result of recent developments it is now possible to readily produce and provide information which effectively shows the ‘real’ picture for any selected time period. It is important that advantage now be taken of these capabilities.
It is not uncommon for a person’s perception about what has happened to be quite different from what has actually occurred. By monitoring and reporting using transparent noise descriptors it is possible to have a meaningful debate with a person about what has actually happened. For example, a person may believe that aircraft start flying over their home at 6.00am every Sunday morning. By keeping accurate records in the form of transparent information the veracity of this can be checked and shared with the complainant. This enables the two parties to discuss the issue using the same language.
In recent years most complaints about aircraft noise at Australian airports have come from residents living in areas outside the conventional (ANEF) noise contours. This has been a key driver in community demands for information on the location of, and the level of activity on, flight paths. This type of information has proven to be useful both because it is much more comprehensible and because it generally extends to areas well outside those covered by the conventional contours.
Flight path reporting—present situation
When producing ‘present situation’ noise contours for aircraft noise information purposes, it is considered very important that comprehensive flight path information be provided which extends a long way from an airport to areas well beyond the outermost noise contour line. A weakness with all aircraft noise contours is that they can give the impression that there is no noise outside the contours, therefore the production of ‘distant’ flight paths is particularly important to demonstrate that aircraft noise does not stop at the outermost noise contour. For some airports, community interest in the location of flight paths can extend to flight paths up to a distance of 30 to 40km from the airport. In addition, ‘distant’ flight path information shows that the shape of noise contours does not necessarily reflect where a significant number of the aircraft fly—the shape of some noise contours is particularly influenced by the loudest aircraft types and by landing aircraft.
Looking ahead—differentiating between the immediate, near and far future
While it is relatively easy to produce information on the location and usage levels of current flight paths around an airport, it is more complex to generate such information for the future. The level of confidence in such future information will reduce as time horizons or the distances from the airport increase.
During an EIS process for a major airspace change (for example, the introduction of a new runway) it should be possible, given the ‘immediate’ time horizon, to generate ‘distant’ flight path information to good levels of accuracy.
In circumstances where there is no expectation of changes in airspace design around an airport, and trends in demand are not volatile, it may also be possible to generate some reasonably robust future flight path information. This may be possible for areas distant from the noise contours and for a near term horizon.
When developing long term land use planning contours the time horizon can be up to 50 years and hence any flight path assumptions have to be conservative and only extend as far as is necessary to generate the contours. Irrespective of the restricted nature of the flight paths used in developing long term planning contours it is important, for reasons of transparency, that details of the flight paths used to generate the contours be made available to the public if this is requested.
(1) For the purposes of this publication the term Environmental Impact Statement (EIS) refers to the generic environmental assessment process of a project rather than an EIS as defined in various pieces of legislation.
(2) Historic ANEF contours are also used for establishing eligibility for which buildings are included in the Sydney and Adelaide Noise Amelioration Programs. For this application the contours are computed using data on flight paths, aircraft types, etc depicting what actually happened in a previous year rather than using a future projection as is used for computing land use planning contours (strictly these are referred to as Australian Noise Exposure Index (ANEI) contours).