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These contours are not operative for land use management or regional council policy. The CRPS has the operative contour and these <\/b>remodelled<\/b> contours are for consideration as part of the CRPS review.<\/b><\/font><\/u>
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Why Two Sets of 2023 Updated Air Noise Contours?<\/b><\/div>
Two sets of updated noise contours were modelled based on two different approaches to runway utilisation (three-month and twelve-month average usage). <\/div>
The two sets of contours are referred to as: <\/div>
Outer Envelope: <\/b>Three-month average runway utilisation<\/div>
Annual Average:<\/b> Twelve-month average runway utilisation <\/div>

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What is Runway Utilisation and How Does it Affect Noise Contours?<\/b><\/div>
The direction aircraft approach and depart an airport is generally dictated by wind direction as aircraft operate most safely into a headwind rather than a tailwind or crosswind. Runway utilisation is the percentage of time aircraft use each runway direction as dictated by the wind.<\/div>

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Due to this reliance on the wind, the average noise experienced in the surrounding community from aircraft over a period of days or months depends on the average wind direction over that time. Air noise contours are based on the average Ldn (the day-night weighted noise exposure) over a period of months. NZS 6805:19921 recommends a three-month period, or alternative period agreed between the airport and territorial authorities.<\/div>

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For some airports the three-month noise exposure is similar to the 12-month noise exposure. This occurs where operations are consistent throughout the year and the wind direction statistics are stable throughout the seasons. In situations like CIA, which has four runway directions and variable seasonal wind conditions, the three-month noise exposure at a given location in the community can vary considerably throughout the year. For this reason, preparing air noise contours for CIA in accordance with NZS 6805 requires consideration of these seasonal fluctuations.<\/div>

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The outcome of the recontouring study was to model two options for runway utilisation referred to as Outer Envelope<\/b> and Annual Average<\/b>.<\/div>

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The 2008 Noise Contours<\/b> were based on the three-month runway utilisation on the crosswind runway, and twelve-month runway utilisation on the main runway.<\/div>
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Outer Envelope Noise Contours<\/b><\/div>
 The Outer Envelope is a composite of four scenarios which represent the highest runway usage on each runway over a three-month period. The highest runway usage is determined from a review of 20 years of runway usage at CIA. The outer extent of these four noise contours overlaid, is taken to form the final Outer Envelope noise contour. For any given location in the surrounding community, the Outer Envelope describes the busiest three-month noise exposure predicted for that location.<\/div>

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Annual Average Noise Contours<\/b> <\/div>
 The Annual Average is a single noise contour (not a composite) to represent the noise exposure over an entire calendar year instead of the busiest three months. The runway utilisation applied for this option is the historical annual average based on 20 years of data.
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How are the Air Noise Contours Applied?<\/b><\/div>
There are four air noise contours that perform different roles in the planning framework. One is used solely for compliance purposes to control the permitted level of aircraft noise. Three contours are used for land use planning purposes. <\/div>
Compliance Contour:<\/b> One contour is applied to manage aircraft noise. This contour definesthe permitted level of noise from aircraft operations over three months and is used to assess compliance, this is: <\/div>
\u2022 65 dB Ldn <\/div>
Land Use Planning Contours: <\/b><\/div>
Three contours are applied in the planning maps for the purpose of land use planning controls. These are: <\/div>
\u2022 Air Noise Boundary (ANB)<\/div>
\u2022 55 dB Ldn <\/div>
\u2022 50 dB Ldn
<\/div>

<\/div>
Air Noise Boundary <\/b><\/div>
(Composite 65 dB Ldn and 95 dB LAE)<\/div>

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The Air Noise Boundary (ANB) applies in Christchurch City only for land use planning purposes. New activities sensitive to aircraft noise are prohibited within the ANB. <\/div>

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The ANB is a composite noise contour defined by the outer extent of the 65 dB Ldn contour and the single event 95 dB LAE contour for the noisiest aircraft operating frequently at night-time. For CIA, the single event 95 dB LAE contour is used as a threshold for sleep disturbance at night. NZS 6805:1992 recommends new noise sensitive activities are prohibited inside the ANB and that consideration is given to single event noise at night when defining the ANB. <\/div>

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Difference between ANB and 65 dB Ldn Compliance Contour:<\/div>
The ANB and the 65 dB Ldn Air Noise Compliance Contour are not the same. The ANB is a composite of the 65 dB Ldn contour and night-time single event contours whereas the Air Noise Compliance Contour is just the 65 dB Ldn contour. Land use controls do not apply inside the 65 dB Ldn Air Noise Compliance Contour, only inside the ANB. 
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55 dB Ldn Contour <\/b><\/div>
The 55 dB Ldn contour defines the area within which acoustic insulation standards apply to new noise sensitive buildings. <\/div>

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The acoustic insulation standards set indoor noise criteria to be achieved. These criteria are generally achievable at levels below 55 dB Ldn outdoors without the need for acoustic insulation measures. Therefore, the 55 dB Ldn contour is used as the threshold for acoustic insulation requirements on the planning maps in Canterbury.
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50 dB Ldn Contour<\/b><\/div>
The 50 dB Ldn contour represents the area affected by aircraft noise where the planning framework works to avoid new noise sensitive activities developing.<\/div>

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The Canterbury Regional Policy Statement references the 50 dB Ldn contour with respect to avoiding new noise sensitive activities. The three district plans include the 50 dB Ldn contour in the planning maps, objectives and policies.<\/div>

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The avoidance approach inside 50 dB Ldn recognises there are aircraft noise effects below 55 dB Ldn. 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