Noise around the airport
Why and how is the noise around airports measured?
The noise from planes is measured for many reasons. It is important to know whether the noise levels are going up or down over time, and if so, by how much.
In Britain, this noise is 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). This averaging-out means that the day’s high and low levels are levelled out to give a single figure. The Government calls this averaged decibel measurement ‘LAeq’, and this is the most common international measure of aircraft noise. As a measurement, it means ‘equivalent continuous noise level’.
What’s the average noise level near you?
In the UK, Government research indicates that people start being concerned by aircraft noise at 57dB, averaged over 16 hours (57dB LAeq). They use this as the starting point in airport and aircraft noise policies.
To show where the different average noise levels are around the airport, the Government has developed maps showing ‘noise contours’. Below is the ‘noise contour map’ for the area around Gatwick. The contours are an irregular shape because you get more noise at the ends of the runway (where planes take off and land) than at the sides.
The map here shows the contours for 2009, combining noise for all flights, regardless of the wind direction and therefore of the direction the planes were flying.
We produce a number of community reports for where our noise monitors are located. Read your local report here.
How many people are affected?
In the last 20 years the 57dB noise contour has shrunk. This is because aircraft are quieter than they used to be. As a result the number of people who live within this noise contour has reduced.
In 1993, there were 14,600 people in the 57dB noise contour around Gatwick. By 2011 this had reduced to 3,050. This is despite a rapid growth in air travel at the same time, from around 191,000 flights a year in 1993 to 244,741 in 2011.
Many people are not bothered by aircraft noise during the day, but they can be affected at night.
Gatwick is allowed to operate a limited service at night. There are restrictions on the level of night time noise that is allowed and the number of planes that can fly at night. On average, Gatwick has 45-50 flights a night in the summer, and 18-20 a night in the winter.
The rules for night time
Until 1962, the government had no policy on night noise, and airlines were free to fly into and out of the airport at any time.
Since 1962, in response to increasing community concern about noise, the government has tightened the rules. But there is not – and never has been – a ban on night flights. The government allows them because it sees them as being important for the well-being of the airline and travel industries, and for the UK economy as a whole.
The night time rules apply from 23:00 until 06:00. There is also a ‘shoulder period’ at either end of the night, with slightly less strict rules – that is 23:00-23:30 and 06:00-07:00.
From 23.30-06:00, the rules allow for a limited number of flights and a limited amount of noise over the whole summer or winter season. The number of flights is based on a points or ‘quota’ system relating to each plane’s noise levels.
On top of the quota system, there is also an absolute limit on the number of flights permitted at the airport. Under the quota system, the airport has a total number of ‘quota points’, which are then used up by night time flights. Different types of planes use up different numbers of points, depending on how noisy they are.
The noisiest aircraft use 16 points of the quota, and they’re called QC16s (QC = Quota Count). The next noisiest have eight points – QC8s. As planes get quieter, their points get smaller until the quietest planes have just half a point or are exempt altogether.
During the night quota period the noisiest types of planes are not permitted to be scheduled. Because there is a limit on the airport’s total quota of points for night-time flying, this system encourages airlines who want to fly at night to use the quietest aircraft.