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Measuring aircraft noise

For many years, noise created by aircraft has been measured by averaging out the noise levels during the day (a 16-hour day) during the summer period. The amount of noise is given in decibels (dB).

Averaging-out means that the day’s high and low levels of noise are levelled out to give a single figure. The Government calls this averaged-out decibel measurement “LAeq”. This is the most common international measure of aircraft noise. It means “equivalent continuous noise level”.

In the UK the Government says people start to become significantly annoyed by aircraft noise at 57 dB LAeq. This figure is used as the starting point for policies on managing aircraft noise around airports.

The Environmental Research and Consultancy Division (ERCD) of the Civil Aviation Authority produces maps annually on behalf of the Government which indicate which areas fall within the area subject to 57 dB LAeq.

The maps for 2010 were published by the Government on 7 October 2011. The report below contains the published LAeq contours for 2010. These are based on the actual split of easterly and westerly operations during 2010.

More noise is experienced at the end of the runways (where aircraft take off and land) than at the sides.

View the full ERCD report relating to the 2010 Noise Exposure Contours (6.2MB PDF)

Aircraft manufactured today are much quieter than they were 40, 30 or even 20 years ago, and these will be replaced by even quieter aircraft in the future.

In fact, due to technological advances and improvements made in noise control methods, between 1980 and 2006 the number of people living within the 57dB LAeq contour has fallen from 2 million to around 252,000. This is despite the fact that during the same time runway movements have increased from around 273,000 to 477,000.

The government was required to produce strategic noise maps for 2006 and airport operators were required Noise Action Plans based on these maps. The latest strategic noise maps produced are available on the Civil Aviation Authority's (CAA) website under ERCD report 0706.

In addition to the LAeq contours, the strategic noise maps consider Lnight and Lden contours.
Lnight is the average sound level over the eight-hour night period of 23:00 – 07:00.

Lden is the day, evening, night level. It is a logarithmic composite of the Lday, Levening, and Lnight levels but with 5 dB(A) being added to the Levening value and 10 dB(A) being added to the Lnight value. This to take account of the fact that noise during the evening and night tends create more disturbance and annoyance.

ERCD report 0706 shows that the estimated population living within the 55Lden contour in 2006 was 756,000. The estimated population within the 50Lnight contour for 2006 was 207,400.

In our Noise Action Plan, we have committed to produce these contour maps annually. During 2011 we commissioned ERCD to produce various contour maps based on 2010 data – View their report here.

However, whilst the noise created by individual aircraft has fallen, many people are now concerned about the increased numbers of aircraft and the routes they fly. Some people feel that contour maps do not adequately describe this issue. At Heathrow we have therefore chosen to provide maps showing typical tracks of where aircraft fly.

The measurement of noise is a technical issue and is not always easy to explain or convey. Heathrow is therefore closely following research into other metrics which may assist understanding of aircraft noise and provide better methods of giving people the information they find useful. Other metrics which are used to describe noise (including those referred to above) are explained in ERCD report number 0904, which is available on the CAA website.

In our Noise Action Plan we committed to work with stakeholders to formulate a regime to track and describe our noise impact. The goal is to establish a range of metrics to describe the noise impact of Heathrow which will meet the needs of a variety of stakeholders. As part of this work we have commissioned independent consultants to research and produce metrics which will assist communication and understanding of how areas are affected by aircraft noise.

You can also assist by telling us what you may find useful. For more information, or to provide your feedback on the website, please contact us.

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