How the Disruption Index is calculated

Our standard model for the Disruption Index is a weighted lag indicator that represents the expected level of disruption caused by aircraft traffic at a specified location. The higher the index value for a location the higher will be the expected level of disruption caused by the aircraft, both visually and by noise output.

The Index is calculated by analysing and blending some 500,000 flight data points that occurred during the busiest travelling times i.e. Christmas (December to January) , Easter (whole of April) and Autumn Bank Holiday (whole of August). Flights below 1500 feet and not considered as the tend not to be non-commercial. Due to the 2020 COVID virus aircraft traffic volumes for the year are not suitable for our analysis and therefore 2019 datasets are used instead.

In the context of our Index, aircraft flight events are considered as being disruptive if the following criteria is met; a) there are 4 or more flights within a single hour all of which are below 26,000 feet as this tends to create a continuous low level disturbance , b) flight events below 8,000 feet, c) direction of travel i.e. departures vs. arrivals, and d) the flight events existed for more than 7 seconds within the defined 1 square mile airspace bubble .

However, if the number of the disturbance flight events is less than 2 within a single hour then those 2 events are considered as one-off and not included within the Index.

Refinements to our standard model are possible, please see our customised survey offering.

The scale of disruption is categorised by eight bands as shown in the table below.

NoneThere are no detectable regular disruptions.
MinimalMinimal regular aircraft disruptions i.e. not frequent or regular. The Index range is between 0.1 and 3.9.
OccasionalThe are Occasional but irregular aircraft disruptions. It is highly likely the location is on a flight route. The Index range is between 4 and 6.9
FrequentFrequent aircraft disruptions i.e. tends to be regular and will be noticeable at defined times of the day. It is highly likely the location is on a flight route or even on a secondary flight corridor. The Index range is between 7 and 11.9.
Very FrequentFrequent aircraft disruptions i.e. tends to be regular and will be noticeable multiple times of the day. It is highly likely the location is on a flight corridor or in a flight holding stack. The Index range is between 12 and 15.9.
HighHigh volumes of aircraft disruptions i.e. tends to be very regular and will be noticeable at anytime of the day. It is highly likely the flights are low and the location is on multiple flight paths, or primary flight corridors or a holding stack. The Index range is between 16 and 19.9.
Very HighVery High volumes of aircraft disruptions i.e. tends to be very regular and will be noticeable at anytime of the day. It is highly likely the flights are low and the location is on a departure and arrivals flight path. The Index range is between 20 and 25.9.
Extremely HighExtremely High volumes of aircraft disruptions i.e. tends to be very regular and will be noticeable at anytime of the day. It is highly likely the flights are low and the location is on a flight path or primary flight corridor. The Index range is 26 upwards.


  • Aircraft disturbance is subjective and its effect can be impacted by other background sounds such as road noise.
  • Your life-style. I.e. those working from home or retired tend to be more sensitive to aircraft disturbances that occur throughout the day.
  • Aircraft flights frequently occur at weekends, on Bank Holidays and also between 6.00 pm and 7.00 am Monday to Friday. This makes it easy to under estimate the scale of aircraft disturbances as at these times it’s difficult to survey manually.

Your personal Airspace bubble

All of us live inside our own personal Airspace bubble but how do we know what’s going on in that bubble and how that activity could be impacting the quality of our lives?

In the context of this posting an Airspace bubble is a 1 mile radius from a specified point such as our homes, holiday locations or outdoor leisure spaces.

The focus of this post is on how to measure the impact of commercial Aircraft within our Airspace bubble. Firstly we need to define impact before we can carryout an assessment. Firstly we ignore all aircraft above 26000 feet as above this height the noise is not generally material . We also ignore aircraft that share our bubble for less that 7.5 seconds as it implies the plane’s noise would not represent a real disturbance.

Having given this much thought we don’t believe disruption is a discussion about the individual aircraft that share our Airspace bubble but more about the aggregation of flights within our personal space at specific times of the day and at specific days of the week.

With this in mind our assessment is based on all flights that share our Airspace at the same time for periods greater than 7.5 seconds and below 26000 feet. This definition provides us with an understanding in a language which we can relate to. For example, we could say that between 6pm and 8pm on a Friday, Saturday and Sunday you will clearly hear and see aircraft 80% of the time.

Even so you personally may find these facts perfectly acceptable or tolerable but at least you now know.

Homebuyers – time to lobby for an extension to the Local Authority Searches so they document local aircraft corridors and flight paths.

Part of the process of buying a new home is for the buyer’s solicitor to perform a Local Authority search. But why? The conveyancing solicitors will say it’s to inform and protect the Homebuyers from any material surprises such as; flood plains, gases, landfill, historic land usage and permissions, planning issues, and detrimental long term town plans.

However, what the current Local Search does not include is any reference to the existence of Aircraft corridors, flight paths and known flight holding stacks within the area. Why?

One of the reasons “why” is because Local Authorities and District Councils believe they are powerless as they don’t own or manage the flight paths and corridors. Your local MP will also echo this sentiment too. So who is responsible and is the required information available?

The answer may surprise you as it’s not the airports themselves but a government agency known as NATs. NATs is responsible for the movement and positioning of aircraft whilst in UK airspace.

Experience tells us that the flight corridors and paths, created and managed by NATs, are very difficult and costly to change once established. So if you find yourself in a situation where you are being disrupted by aircraft it will be almost impossible to change and you will get little sympathy from the Government agencies . Meaning, it’s best to find out about the existence and usage of flight corridors and paths prior to purchasing a property. I.e. be informed! But how?

Unfortunately the “how” is not at all straight forward as although the flight information is available to the Government bodies there are no policies, guidance or standards about how the flight information should be presented to the payers of Stamp Duty.

Our objective is to lobby the UK Government departments to they can make the required changes to the Homebuyers Local Authority Searches to document the existence of local aircraft movements and flight corridors and paths. We believe the public have the right to know.

If you are interested in joining us on this journey then please leave your comments on the contact form below.

Aircraft disruption above our heads

Finding out what’s going on in the sky above your house or flat in the UK is almost impossible as there is no usable public information about aircraft flights and subsequent potential disruption.

Solicitors, Estate Agents and Home Buyer surveyors won’t know either. Aircraft flights are not in scope of Local Authority and even the airports and government authorities such as NATS, if asked, will provide a very blended superficial summary for the entire area that will not be specific to your plot. We think this is wrong as we deserve to know, hence the need to escalate with our MPs.

Software Apps such as flight trackers will not provide the required information that’s specific to your plot.

Thanks to the new Aircraft Traffic Survey service it’s now possible to avoid that sinking feeling when you realise you have just purchased a new home that is subject to frequent or low level over flights caused by arrivals, departures and flight holding stacks.

However, the the noise and visual impact of aircraft can be very subtle and it’s easy and unfair to dismiss an entire area. Just 0.5 mile in one direction or another can make a huge difference to the scale and type of disruption.

Covid 19 – Is Gatwick Airport now in Terminal Decline?

Over the past 10 years Gatwick Airport has been actively pursuing an expansionist agenda which has been implicitly supported by many of the government bodies but opposed by the millions of residents of Sussex, Kent and Surrey. However, have events such as Covid-19 and Regional Airport investment now overtaken Gatwick’s agenda?

Since Covid-19 the airline industry itself has challenged Gatwick’s role by reducing its presence and dependency on Gatwick Airport by realigning their fleets to other established Hub airports and the newly expanded regional airports such as; Stansted, Southampton, Bournemouth, London City etc.

This begs the question about the future need for Gatwick Airport in the post Covid-19 era as the local regional airports now have invested in the infrastructure to accept new business and routes. This leaves Gatwick Airport, located in the South Downs and surrounded by AONBs, in a position to transform and become an airport for predominately the residents of the Home Counties only.

This means that tens of thousands of Gatwick’s passengers would no longer slavishly drive hundreds of miles around the M25 and M23 as they would enjoy the benefits of using their expanded regional airport capacity.

This creates a huge number of exciting new opportunities for Gatwick Airport and the surrounding area with the land being repurposed as a “next generation” holiday and leisure destination such as the Eden Project, with great access to the Captial, the South Coast resorts, beautiful countryside, and of course Heathrow Airport.

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Arrivals Flight Holding Stacks

The Aircraft Traffic Survey service is showing a growth in the use of the 90 second Arrival Holding Stack for flight separation which is a process used by NATs to prevent “bunching” when Arrival flights transition from unregulated airspace into the regulated airspace which is below 6,500 feet.

Understanding the existence of aircraft Arrival routes and Holding Flight stacks is very important when deciding on the area in which to purchase a home as the existence of flights means some form of disruption. It’s not something to discover once Stamp Duty and Solicitors costs have been paid.

Flight Arrivals, unlike flight Departures, are less regulated and are used at any time, 24 hours a day, 7 days a week. The Operational Management policies for flight Arrivals are totally owned, designed and managed by a Government body know as NATs. The NATs Air Traffic Controllers are responsible for the physical routes and altitudes taken by the individual aircraft when travelling within UK airspace. Some Air Traffic Controllers are based in regional centres, and others are seconded to the individual airports. NATs also subcontracts roles and responsibilities including the Air Traffic Controllers to 3rd party service companies. This structure makes change very complex to implement and over extended time frames.

NATs have created a number of Arrival flight holding stacks over the UK that are typically located 30-40 miles away from the destination airport. Their design resembles 7 oblong shaped circuits arranged vertically, the lowest being 7,000 feet and rising to 15,000 feet. The circuits are 10 miles in length and 6 miles wide and take around 4 minutes for an aircraft to navigate although many aircraft are “pulled” from the stack by NATs after 90 seconds by performing a tight banking manoeuvre.

Holding stacks tend to have a single entry point and multiple exit points and often hold 5-6 planes at the same time and as one aircraft exits another enters. Additionally, because they occur at above 7,000 feet they are very lightly (not) regulated for noise and air pollution even though the aircraft traffic volumes can be very high e.g. 30-60 planes per hour.

When is an Arrival Holding Stack used?

The NATs Air Traffic Controllers will decide and instruct the pilot when to pass directly through an Arrival holding stock or at what altitude to join the stack. Factors that can increase the usage of the stack include;

  • delays at the destination airport i.e. reached full capacity (highly likely)
  • flights arriving before the airport opens (highly likely)
  • flights arriving early (highly likely)
  • flight separation (highly likely)
  • bad weather (unlikely)
  • emergencies (unlikely)

Fortunately not all plots and homes are impacted in the same way even though they are in the same geographic area. This is because aircraft disturbance can be very localised. The overall impact is identified and assessed by the new Aircraft Traffic Survey service.