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How we calculate overflight

An aircraft flies within the analysis cone and is successfully counted

The following video explains how our system calculates location-specific data used on this website:

1km x 1km grid over the local area to show how we divide up our analysis

The grid

To be able to analyse the number of flights over an area around the airport, we have created a grid of identically sized, 1 kilometre by 1 kilometre squares which extend for up to 50 miles from London Gatwick.

How we count the number of flights

We start by drawing a cone at the corner of each grid. Using the location that you provided when you entered the site, we determine the nearest cone to you.

Flights that pass through each cone are recorded and that data is presented on this website.

To avoid underestimating the flights in each area and to fully cover all locations in our grid, we lower the cone 2,600 feet (800 metres) into the ground. The cone extends up to 7,000 feet (2.1 kilometres) above local ground level and at the very top, the cone is over 5 kilometres wide. 7,000ft was chosen as an upper altitude limit as according to the Air Navigation Guidance, this is the highest altitude for which noise management is prioritised above or equal to greenhouse gas emissions.

Why we use a cone

We use a cone because research undertaken by the United Kingdom Civil Aviation Authority identified that a cone best aligns with how we determine if an aircraft has overflown a location or not.

The 48.5-degree angle of the cone was selected as it incorporates an evaluation of noise, in that if one aircraft flew directly above the observer, followed by a second aircraft off to the side along the 48.5 degree line, the second aircraft would be 3 decibels quieter than the first.

Where does the data come from?

All data used in our system comes directly from the London Gatwick Noise and Track Keeping (NTK) system, which receives flight data from Air Traffic Control radar.

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How is aircraft noise generated?

An aircraft in the sky

What is aircraft noise, and how is it generated?

Aircraft noise is sound emitted by aircraft during operation, which results from the movement of the aircraft through air and the propulsion required to do so. In specific, it is caused by:

  • Engine noise
    • Combustion
    • Fast moving parts, e.g. the fan or propeller
    • Hot exhaust air mixing with ambient air
  • Airflow around the airframe
    • Flaps
    • Landing gear
    • Fuselage and wings

In general, the engines will cause the most noise during take-off when they are running a high power settings. During approach, not much thrust is needed and noise caused by airflow around the airframe will be more apparent. Different aircraft produce different noise depending on size, engine type & number and other factors.

What influences aircraft noise?

The aircraft noise observed on the ground can sound very different depending on a number of factors including:

An aircraft above tall city buildings
  • The phase of flight (departure, cruise, approach)
  • The altitude above the ground
  • The lateral distance from the observer
  • The weather conditions

Whilst these factors influence the sound that a noise monitor would measure, the perception of noise by humans is more complex. It depends on our local soundscape (or the day-to-day noise that we all experience) how much, or how little aircraft noise we receive.

For example, if you live in a noisy area, potentially within a town or city, or close to a road, the background noise level from those sources is likely to mask the sound of aircraft noise. Conversely, in a quiet area the masking effect isn’t present and the same aircraft is likely to be more noticeable.

It is important to note that annoyance is a personal experience, what might be annoying to one person may not be annoying to another. The airport takes noise monitoring seriously and has an active programme to monitor, analyse and report on the aircraft and background noise level in the local community.

Looking out of an aircraft window towards the wing and engine

Has aircraft noise changed?

Modern aircraft produce far less noise than older aircraft, producing around 90% less noise than the aircraft which were operating in the 1960s and the noise contour around London Gatwick has recently reduced in size despite a rise in traffic (not including the COVID-19 pandemic period).

This portal has been designed to provide transparent information on the traffic and noise levels. London Gatwick will keep the public informed through our engagement groups.

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Our monitoring system

An aircraft flies over a noise monitoring terminal

Environmental monitoring and management is crucial for responsible airport operations. It allows the airport to understand its impact on the local environment and community and what can be done to manage and mitigate those potential impacts.

The system this airport uses is called ANOMS, which stands for Airport Noise and Operations Monitoring System which provides the Noise and Track Keeping (NTK) capability. It is a complex solution featuring both hardware in the form of remote sensors, radar data collectors as well as advanced analytical tools.

ANOMS uses a number of fixed or temporary noise monitors in the local area, these are generally located under or near flight paths. The monitors detect and send the noise levels every second 24 hours a day, 7 days a week to a central system.

A ‘noise event’ is created when the system detects noise exceeding the background or local noise level for an appreciable amount of time. This could be due to any number of factors, be it local birds, cars or an aircraft. By continuously monitoring the noise level and integrating data from Air Traffic Control (ATC) our systems can determine if the noise event was generated by an aircraft, or another source.

You can find out more by watching this video:

Data collection and noise event detection

The system combines data from remote noise monitors deployed in the local community and in proximity to runways and flight paths. These run 24 hours a day 7 days a week, continuously collecting and sending noise data through to ANOMS, creating ‘noise events’ when the noise level rises above the background noise level and meets pre-set thresholds.

An aircraft overflies a noise monitoring terminal

Flights are tracked using data direct from ATC radar systems, in effect it is the same data used by ATC to safely control aircraft in the sky. ANOMS uses this data to record the path flown by the aircraft and by identifying which noise monitors the aircraft flew close to and when. In simple terms, identify the noise events that were generated by that aircraft can be identified and linked.

The process is complex and, whilst it can identify noise events due to aircraft, it can also identify events that were not generated by aircraft. These are known as community events and could be generated by birds, wind, vehicles on a road or even emergency vehicle sirens. In effect, any noise that we could hear on a day-to-day basis that isn’t generated by an aircraft.

By considering the aircraft and community noise, a detailed picture of the local soundscape can be built, allowing the airport to understand the potential impact of operations in the local community.

Other data types are added to the system to gain a better insight into what happened and why. Weather data is another extremely useful feed – strong winds or thunderstorms may alter where aircraft fly, whilst clouds may reflect sound back towards the ground, changing how that noise is heard.

How the system is used

The ANOMS system is used by different stakeholders in the airport management structure:

  • Community engagement teams can view enquiries, complaints and submissions from the local community, accessing the detailed data available within ANOMS to respond to the local community. This includes detailed weather and operational data to explore and analyse unusual operations.
  • Operations teams can use the detailed reports to assess and continuously improve the airport.
  • Management can assess trends, determine performance and provide direction.

In summary, the system can analyse a great deal, but two major items – quickly identify anything that was anomalous and discover why, and also monitor the day to day operations of the airport, presenting reports to management and the community. The historical data gained can then be used to plan for the future and improve operations.

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How many aircraft fly near my area?

The following chart demonstrates local air traffic around your area – total flights per day for the month. The number and type of flights over your location can vary, even on different days, which is driven primarily by wind direction and hence the operating mode of the airport – the flow.

You can easily determine if an aircraft is overflying your area by looking for the tail, if you can see the tail, chances are the aircraft is too far away from you to be counted in our statistics:

Mousing over the chart will give you detailed figures. Historical flights from previous months are available via a drop-down. The data is refreshed monthly with new data available typically in the middle of each month. Please keep this in mind as the most recent datasets may only be partially complete.

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Detailed dashboard for your area

Pulling together much of the other panels for frequency of flights, regularity, and altitude, this detailed dashboard compiles it all into one space for your review.

Additionally here, we include aircraft category – what type of aircraft they are, whether this is small civil aviation (propeller driven), or business jet, helicopter, commercial jet, or even military.

Information regarding the source of the overflight is also displayed, which is especially useful if there is more than one airport in your local area.

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How frequent are flights in my area?

There are a number of factors that influence the frequency of flights:

  • Firstly, the number and frequency of flights will vary on a daily, weekly and yearly basis due to differences in airline schedules. The airlines schedule flights in response to consumer demand. This is particularly the case around holiday periods.
  • Secondly, the runway in use at any given time will also vary, largely due to the wind conditions. Each runway has its own set of flight paths, and each flight path will affect different areas. As the runway in use changes, the flight paths change, and so too do the areas affected.

This chart displays the average number of flights per hour over the entire months. Mousing over the chart shows more details, with historical months available via the dropdown. As mentioned in the previous section, data is refresh in the middle of every month.

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How high are flights in my area?

A depiction of a chart showing how many flights have flown the area in 1,000ft vertical bands

The altitude of aircraft can vary due to a number of factors. It could depend which airport the flight is going to, or from and whether it is an arrival or departure. Arrivals are typically following a steady descent to the runway whilst departures are typically following a steeper path as they climb away from the runway.

A core function of Air Traffic Control (ATC) is safety, and one of the primary ways in which this is achieved is by maintaining either lateral or vertical distances between aircraft. When close to airports lateral separation is used, but when at higher altitudes, vertical separation is used with aircraft typically separated by around 1,000ft. This can sometimes be seen in the overflight data for your area.

This chart shows the height of aircraft overflying your area in 1,000ft increments. Mouse over it for more figures and detail. A dropdown menu allows you to view historical months for comparison and trends. The data is refreshed monthly, generally in the middle of the month.

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