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Environmental Analysis for Brisbane

Methodology

Smart Tracking has been successfully trialled at Brisbane since 2007. During this time more than 32,000 approaches have been flown.

As part of the evaluation of plans to make Smart Tracking permanent, we have analysed potential changes in aircraft noise distribution between 2010 and 2020, with and without Smart Tracking being used.

Our analysis assumes 85 per cent of all jets will use Smart Tracking by 2020. Around 20 per cent of jet arrivals to Brisbane used Smart Tracking during the Brisbane Green trial.

The on this page is based on a forecast growth in air traffic of four per cent a year. However, we have analysed only the difference in noise impact which could be attributed to the permanent use of Smart Tracking.

All Smart Tracking at Brisbane is done within existing long-standing flight paths.

How is aircraft noise measured?

Noise is measured using A-weighted decibels, or dB(A) for short. This is a representation of the loudness of sounds in air as perceived by the human ear.

To measure the maximum sound level of a single noise event, LAmax is calculated.  This indicates the highest noise level a person on the ground would hear from a single aircraft overflight (arrival or departure).

To measure average sound level over a particular time period, the equivalent continuous sound level, or LAeq, is calculated.

For example, an Leq24 of 40dB(A) indicates that the sound energy produced by aircraft flying  overhead periodically is equivalent to a constant sound of 40dB(A) over 24 hours.

Some useful rules of thumb:

  • a change in LAmax of at least 3 dB(A) is generally required before a difference in sound level may be noticed
  • an increase in LAmax of 10 dB(A) is required before most people perceive the sound to be twice as loud
  • a change in LAeq of 3 dB(A) could be caused by doubling the number of overflights or by all of the aircraft being 3dB(A) louder
  • a sound outdoors will generally be 10-15 dB(A) quieter indoors due to the attenuation by the building.

Approaches to Runway 01

There are three proposed permanent Smart Tracking routes for approaches over land to Runway 01 at Brisbane.

Aircraft not equipped for Smart Tracking cannot normally use Tracks 1 and 3 during bad weather. Track 3 can also not be used after dark.  Instead, aircraft are required for safety reasons to use Track 2 at these times.

Smart Tracking aircraft are not constrained by these conditions. As more aircraft are equipped to use Smart Tracking, it is expected flight distribution between these three tracks will, over time, more closely resemble typical daytime usage patterns.

Track 1 is the approach for traffic arriving from the north.  The level of noise of any individual flight is not expected to change for most communities under this route. A few locations may experience decreases in LAmax by up to 6 dB(A) or increases by up to 5 dB(A).  The 24-hour average noise level may decrease by up to 4 dB(A).

Track 2 is the overland straight-in approach.  There should be no change to the maximum noise exposure of any individual flight to any community.  A few areas at the southern end of this route may experience increases of up to 5 dB(A) in average noise level over a 24-hour period. Most areas are expected to experience no change.

Track 3 is the approach from the south. It is used by about two-thirds of flights arriving in Brisbane. While there should be no change to the maximum noise exposure of any individual flight to any community, the final segments of the Smart Tracking route are offset slightly from the centre of the current flight path corridor. Some areas close to the airport may experience more noise events.  Other areas will experience less noise events than they do now.  No perceptible change is expected to the average noise level over a 24-hour period.

Approaches to Runway 19

There are five proposed permanent Smart Tracking routes for approaches to Runway 19.  These are mostly over Moreton Bay.

Track 4 is initially over land but at high altitude (above 5000 ft or 1500 metres). There is unlikely to be any change in aircraft noise that is noticeable by the community.

Track 6 takes aircraft further away from residential areas on North Stradbroke Island.  The noise impact to residents from aircraft is already very low and will reduce further.

Tracks 5, 7 and 8 are over Moreton Bay and will not result in any changes to noise impacts on communities.