Measuring aircraft noise
Measuring noise and describing its impacts is an inherently complex process. Some individuals find noise more disruptive than others. Some types of noise have a greater impact on people than others. And the nature and severity of the impact can vary from person to person. Any attempt to define and measure noise therefore has limitations, and cannot fully capture the spectrum of personal experiences of noise. Nonetheless, seeking to quantify noise is an essential foundation stone for any effort to address the noise challenge.
Different ways of measuring noise
There are many ways to describe noise. Some definitions are based on noise levels at a specific time, some are based on maximum or peak levels that people experience, and others are based on averaging noise over a defined period.
The impact of individual flights is often explained using the maximum noise level of a plane. However the impact of one plane is not the same as the impact of many. Overall noise impact is often described using an average level of noise which is presented in the form of a noise exposure contour. These contours enable the geographic area and population exposed to particular noise levels to be reported and tracked over time.
Governments in Europe map the areas affected by noise using noise exposure contours.
The UK Government uses an average noise measure known as the ’57 decibel summer Leq contour’. This figure is used as the starting point for policies on managing plane noise around airports. It is an average of the noise levels during a summer’s day (when the airport is busiest) between 7am and 11pm. Past Government research found that 57 decibels marks the threshold above which ‘significant community annoyance’ begins.
In Europe they use a different measure – Lden – which is the level of noise during the day, evening and night. Evening and night are weighted because that is when noise is most disturbing. EU research shows that 10-28% of the population exposed to noise levels above 55Lden could be ‘highly annoyed’.
To view the Government's noise exposure reports and contours for Heathrow and other London airports, visit the Department for Transport's website.
We need more than just noise contours
These methods are not perfect. They allow for mapping to be done and for statistical data to be gathered and compared over time. But we know that they do not necessarily relate to someone’s experience of noise.
People around Heathrow regularly tell us that they want to know about the total flights over a particular location, the time and day of those flights and the noise level of the loudest flight. See Track noise on maps to do this.
We need to balance the problem of noise with the economic benefits of the airport. To do that, we need to keep using the noise contours to allow for some assessment of change over time. However, we recognise this is not the full story. We will continue to talk and listen to local communities to better understand how people experience noise and ensure our approach to managing noise takes this into account.