Official airport noise maps: what they show and what they miss

Most people meet an airport noise map when they are about to buy or rent. It looks definitive: coloured bands spreading out from the runways, with numbers attached. Read properly, it tells you a lot. Read as a verdict on a single house, it can mislead in both directions.

What a noise map shows

A noise map joins places with the same average sound level from aircraft, the way a contour map joins places at the same height. Each band covers a range of levels, and the closer to the runway and its flight paths, the higher the band.

Two things matter before you read any numbers:

• It is calculated, not measured. A model takes a year's flights, with their aircraft types, routes, heights and engine power, and works out the sound at every point. In Europe the models follow ECAC Doc 29; Heathrow's contours, for example, come from the UK's ANCON model, which is checked against noise monitors around the airport. In the US, the FAA's Aviation Environmental Design Tool does the same job.
• It is an average. The figure is the sound energy of all the flights spread across a day, a summer or a year, usually with evening and night flights weighted more heavily. Lden, DNL and Lnight explained covers the measures themselves.

The three kinds of map you will find

EU strategic noise maps

Under the Environmental Noise Directive, every airport in Europe with more than 50,000 flights a year is mapped every five years: 2017, 2022 and next in 2027. The maps show Lden over the whole day and Lnight at night, and are reported from 55 dB Lden and 50 dB Lnight. In England the airport operators are responsible for them; in Ireland, daa draws the map for Dublin Airport. They also give a count of the people in each band, which is where Europe-wide figures come from.

UK annual contours

Several of the UK's larger airports, including Heathrow, Gatwick and Manchester, also publish contours every year, calculated by the Civil Aviation Authority. They show the average summer day, LAeq,16h from 07:00 to 23:00 over the 92 days from mid-June to mid-September, and the average summer night. Heathrow's day contours start at 54 dB and rise in 3 dB steps. That is above the government's lowest level of concern, 51 dB by day; Gatwick asked for a 51 dB contour to be added to its 2022 report. In 2024, Heathrow's 54 dB contour covered about 129 km² and 400,900 people.

Heathrow, Gatwick and Manchester also publish "number above" contours, such as N65: how many planes a day are louder than 65 dB at each point.

US Noise Exposure Maps

In the US, an airport that takes part in the FAA's Part 150 programme, which is voluntary, publishes a Noise Exposure Map. It shows contours at 65, 70 and 75 dB DNL for the current year and for a forecast at least five years ahead. The FAA treats homes as incompatible with noise above 65 dB DNL, unless the community decides to allow them, in which case they should be built with 25 to 30 dB of sound insulation. An airport in the programme must revise its map if a change in operations raises DNL by 1.5 dB or more over homes or other land where the noise is judged incompatible.

How to read the bands

• Find the band, then the measure. 60 dB Lden, 60 dB LAeq,16h and 60 dB DNL are not the same thing, so compare like with like.
• Read the steps as multiplications. The average rises by 3 dB when the number of similar flights doubles, and by 10 dB when it grows tenfold. The FAA gives the example that one very loud flight a day, 10 moderately loud ones or 100 quieter ones can all produce the same 65 dB DNL.
• Check the year and the scenario. A map describes one year's traffic. UK contours may come in two versions: the runway directions actually used that summer, and a long-term average split.
• Treat the lowest band as a line on paper. It marks where reporting stops, not where the noise stops.

Where to find them

• England. Airports publish their strategic maps in their noise action plans, and the larger ones publish annual contours on their noise pages. Defra holds the latest airport maps on its Data Services Platform. Defra's own national noise maps cover road and rail, not airports.
• Scotland. The Scottish noise mapping site includes the maps for Aberdeen, Dundee, Edinburgh and Glasgow airports.
• Wales. DataMapWales holds the 2022 maps for roads, railways and industry, but no airport layer.
• Ireland. The EPA's online maps show the 2021 strategic maps. Fingal County Council's noise action plan for Dublin Airport adds 2023 figures to the 2021 maps.
• Across Europe. The European Environment Agency's NOISE viewer shows the number of people exposed around each major airport, with contours as you zoom in.
• US. The FAA lists Part 150 studies by state; the maps are in the airport's study. The Bureau of Transportation Statistics' National Transportation Noise Map covers aviation, road and rail across the country, but says it is meant for tracking trends, not for judging noise at individual locations.

What noise maps miss

The bad days

An average blends the days when planes pass overhead with the days when they don't. Heathrow's 2024 summer was 80% westerly and 20% easterly, so a street under the easterly approach got its landings on about one day in five, and its average is diluted accordingly. On those days, it may hear a plane every minute or two.

This is why counting loud planes often matches what people notice better than an average. Why average noise hides the problem explains it in more detail.

Everything below the lowest band

People are bothered well outside the bands. A 2023–24 survey for the CAA found one person in ten highly annoyed at about 43 dB LAeq,16h, more than 10 dB below Heathrow's lowest contour. The FAA's national survey found 15 to 23% highly annoyed at 50 dB DNL, far outside any Part 150 contour. The European Environment Agency notes that health effects already occur below the levels countries have to report.

Time

The 2022 round of European maps was based on 2021 traffic in most countries, when flights were still well below normal. Several countries also reported late, so the European figures had to be filled in. Meanwhile, new runways, new routes and busier schedules can move the bands. A US map includes a forecast; a European one only looks back.

What the model leaves out

A map models average aircraft on average routes in average weather. It does not show how high the planes are over your street, what time the first one arrives, or noise from the ground, such as engines running on stands. England's strategic maps leave out ground noise and helicopters altogether.

Use the map as a first filter

A noise map answers one question well: is this area inside an airport's official footprint? If it is, you know to look closely, and whether the home may qualify for airport insulation schemes. If it is not, don't take that as a promise of quiet. Check where the runway lines run, how often the wind sends planes over the house, and how many loud planes it hears on a bad day. Free ways to check aircraft noise compares the tools that help.