How far from an airport is far enough to avoid the noise?

Asking how far from an airport is far enough is a little like asking how far from a railway station is quiet. A house beside the tracks 10 km down the line hears every train; one a street away from the station, off the line, hears few. Planes also use a few narrow lines, and houses under them hear planes a long way out, while houses between the lines can be quiet quite close in.

Direction matters more than distance

Two of our sample reports show it. Kew Green is 10 km from Heathrow, close to the line landing planes follow on westerly days. Winthrop is 1.3 km (0.8 miles) from Boston Logan, where take-offs climb out overhead on northerly days.

"Loud" means above 65 dB outdoors, enough to interrupt a conversation. The house nearly eight times further away hears more loud planes on an average day and night. What decides it is where each house sits in relation to the runway, and how often the wind sends planes over it.

Landing planes stay low for 15 to 20 km

Landing planes line up with the runway 15 km or more before touchdown and descend along its centre line at a shallow 3 degrees, about 170 ft for every kilometre. That slope is why the landing line carries noise so far out.

Over the last year, landing planes at Heathrow were at these heights above the airport:

On the same slope, a plane 20 km out would be at roughly 3,600 ft. Further out still, planes are no longer on one line: air traffic control brings them onto the final approach from wide areas, so they are spread over many kilometres and each street hears fewer of them, higher up. More on the heights in our guide to how high planes fly when landing and taking off.

Take-offs climb faster, then spread out

Close to the end of the runway, take-offs are very loud, as Winthrop shows. But they climb far more steeply than landing planes descend. On westerly days at Heathrow, take-offs were at about 1,750 ft 2 km from the runway and 3,750 ft at 8 km, where landing planes on the other side of the airport are at about 400 ft and 1,400 ft.

Take-offs then spread out. At Heathrow each departure route is a corridor 3 km wide until planes reach 4,000 ft, and after that air traffic control can turn them onto more direct headings. At Gatwick, planes leave their routes at 3,000 or 4,000 ft, depending on the route. At the climb rates we measured, westerly take-offs from Heathrow reach 4,000 ft about 9 km from the runway. Beyond that they fan out, and any one street under them gets a share rather than every flight. On westerly days at Heathrow, for example, about two-thirds carried on west past Windsor and most of the rest turned south over Thorpe.

How far to the side is far enough

A plane does not need to pass straight overhead to be loud. The Civil Aviation Authority's work on overflight, published in 2017, shows what happens as you move sideways from a flight path:

• At 60 degrees above the horizon, a plane is only about 1.5 dB quieter than directly overhead at the same height.
• At 48.5 degrees it is about 3 dB quieter, roughly the smallest difference most people notice. The CAA proposed this angle as one of its tests of whether a plane is overhead.
• Below about 35 degrees, the ground, the air and the plane itself, which shields some of the engine noise, take far more out of the sound, and the level drops away quickly.

What these angles mean on the ground depends on the height of the planes. As a rough guide: if the house is less far to the side of the flight path than the planes are high, they are within about 3 dB of overhead. Once the sideways distance is more than about one and a half times their height, they are below 35 degrees and get quieter quickly.

So the further out along the landing line, the wider the band that hears each plane, even as each one gets a little quieter. How loud a plane is at any of these points also depends on its size and engines, so treat the figures as a guide, not a boundary.

How often the planes come your way

Distance and direction tell you how loud a plane will be. The runway split tells you on how many days. Heathrow says it operates towards the west about 70% of the time over the long run; over the last year, planes landed towards the west on 62% of days and towards the east on 26%, with the direction changing during the day on the rest.

So a house under the eastern approach, such as Kew, has loud landings on most days, while a house under the western approach, around Datchet or Windsor, has them on about one day in four. Both are under a landing line, at similar distances, and their years are very different. Our Heathrow page shows how the split changes through the year.

How to judge a particular house

1. Find the lines. Extend each runway on a map and mark the take-off routes from the airport's maps. Our guide to whether a house is under a flight path covers five ways to do it.
2. Measure along the line. The distance from the runway gives the height of landing planes, at about 170 ft per kilometre.
3. Measure to the side. Compare the sideways distance with that height, using the table above.
4. Check how often each direction is used, and whether the house is under the approach used on most days or the one used on the rest.
5. Count the loud planes on real days. Replay a day in each direction on our free flight map and tap the street.