Causes of aircraft noise
What causes the noise?
If we’re talking basic physics, the noise from a plane is caused by two things: by air going over its fuselage and wings (or ‘airframe’) and by the engines.
Airframe noise occurs when air passes over the plane’s body (the fuselage) and its wings. This causes friction and turbulence, which make a noise. Even gliders make a noise when in flight – and they have no engines at all. The amount of noise this creates can vary – according to the way the plane is flown – even for identical aircraft. Planes land with their flaps down which creates more friction (and produces more noise) than a plane with its flaps up
Engine noise is created by the sound from the moving parts of the engine, and also by the air being expelled at high speed once it has passed through the engine. Most of the engine noise comes from the exhaust or jet behind the engine as it mixes with the air around it.
Modern noise levels
Aircraft 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.
But, of course, even though each individual aircraft is quieter, there are more planes flying today.
This means that the average level of noise is lower than before, but you hear individual planes more often. This makes it even more important that we keep on working to get the noise levels down. On this website we tell you what improvements have been, and are being made to aircraft design to reduce noise even more.
Why am I hearing aircraft noise?
If you are hearing aircraft noise, it will be for one or more of these reasons:
- You live or work very close to the airport, and hear planes landing, taking off and on the ground.
- You live or work under a flight path and hear planes taking off.
- You live or work under the approach path and hear planes coming in to land.
- You live or work under an aircraft ‘stack’ and hear planes in the stack.
- You live or work between a stack and an airport and hear planes as they approach the airport.
Living or working under the approach path
While there are defined flight paths for take-offs, there are none for landings until aircraft are established on the Instrument Landing Systems (ILS), also known as the final approach.
This is because there is less operational flexibility in landing a plane than there is in taking off – because the plane has to line up with the runway from several miles away. This is very different to take-off, where planes can climb steeply and quickly and turn while they climb.
When the Government first set its noise restrictions, it concentrated on take-off noise. This is not only because planes were noisier then, but also because the first jets climbed very slowly and so their take-offs were much noisier than their landings.
How does it all work?
When a plane arrives in the local airspace, or leaves a holding stack, ATC directs each plane on an individual course onto the final approach and brings it into land.
So if you live or work near or under the final approach to the airport – whether planes come from the west or from the east – then you will hear the noise of planes arriving.
Living or working under the flight path
When planes take off, they have to follow specific routes which were set by the Government. These routes, which are 3km wide, are designed to make sure planes avoid flying over areas where lots of people live until they reach a certain height.
At Gatwick those heights are either 2,798 or 3,798ft depending on which flight path the aircraft is on. These heights might seem a little odd but they take account of the fact that Gatwick is 202ft above sea level. ATC measures height above sea level (altitude) which means they are looking for aircraft to reach 3,000 or 4,000ft before they can direct them off the flight path towards their destination.
The technical name for these special flight paths for take-off is ‘noise preferential routes’ (NPRs). They were set by the DfT several decades ago.
Taking off and the importance of wind direction
Another basic aspect of aviation safety is that planes need to land and take off into the wind. They can take off in the same direction as the wind, but this is only allowed if it’s wind up to 5 knots, which is little more than a breeze.
Most of the time at Gatwick, the wind comes from the west so most of the time they’ll fly towards the west.
Therefore, the Government set the take-off flight paths for when the wind is blowing from the west. Of course, we can’t control the direction of the wind. Because of this, the Government has also set take-off flight paths for the opposite wind direction from the other end of the runway, as the map above shows.
What does this mean locally?
It means that on average, about seven out of ten take-offs head towards the west and only three out of ten take-offs go east.
The split in take-off direction is almost completely dependent on the wind direction and speed, and so varies from year to year and month to month. In fact, the length of time that the runway operates in one direction can vary from a few hours to a few months: it all depends on the weather.
If you live under one of these take-off flight paths, then you will probably hear some noise when that particular flight path is being used. If you live beyond the flight path – past the point where the plane reaches 2,798 to 3,798ft – then you might sometimes hear noise when the plane leaves the flight path to head towards its destination.
If you live alongside (but outside) a flight path, you might hear noise if a plane flies outside the flight path. This can happen if ATC tells a pilot to leave a flight path for an operational reason (such as to avoid bad weather). We take ‘track keeping’ (staying on the flight path) very seriously and 98% of Gatwick’s aircraft are ‘on-track’. On this website we tell you what we are doing about this type of noise and how you can find out more information or contact us if you need to.
Other local procedures
There are also a few Gatwick-specific operating procedures. For example, pilots have to avoid flying over Horley and Crawley once they take off. They also have to stay above 2,798 ft over Crawley, East Grinstead, Horley and Horsham and over 1,798 ft over Lingfield when landing.
Living or working under a holding stack
When airports are very busy there can be a build-up of planes waiting to land. To make sure there is a safe gap between each plane landing, ATC keeps these planes circling until they can land: this is called a ‘holding stack’.
The minimum height of the holding stack is 7,000 ft above sea level. This means that the noise from the stack shouldn't cause a nuisance. Of course, this can’t always be the case, and people are sometimes disturbed. This happens more often when a holding stack is over the countryside, where there is little background noise, such as road traffic.
Every airport has several holding stacks and Gatwick has two, designated as ‘Willo’ and ‘Timba’.