Aviation noise and environment in airspace change

The CAA, as the UK’s independent aviation regulator, has primary responsibility for deciding whether to approve an airspace change proposal to the notified UK airspace design. We make these decisions in accordance with the legal framework to consider certain factors which include safety, the environment, the needs of users of airspace and government policy, including the airspace modernisation strategy.

The Secretary of State has given the CAA the function of approving changes to the design of airspace in the Civil Aviation Authority (Air Navigation) Directions 2023.

The Directions require the CAA to develop and publish procedures and guidance for the development, making and consideration of a proposal for a permanent or temporary change to airspace design, or an airspace trial. This procedure and guidance are published as CAP 1616 Airspace Change.

Under the 2023 Directions, the CAA has a duty to decide whether to approve changes to airspace design in accordance with the Airspace Modernisation Strategy. In performing this duty, the CAA ensures that the airspace change proposal aligns with the vision and strategic objectives of the Airspace Modernisation Strategy, as well as any iterations of the Airspace Change Masterplan, where applicable, that have been accepted into that strategy. 

The CAA has developed the CAP 1616 airspace change process to ensure that it meets modern standards for regulatory decision-making and is fair, transparent, consistent, and proportionate. The airspace change process must be impartial and evidence-based and must take account of the needs and interests of affected stakeholders.

The CAA’s airspace change process must operate within the Government’s policy framework. We work closely with the Government to ensure clarity around our respective policy and decision-making roles in the airspace change process. However, the CAA cannot review government policy, nor can it make a regulatory decision that does not give effect to that policy.

You can read more about the CAA’s statutory duties in relation to airspace change on our legislative framework to airspace change page.

Aviation noise can affect human health and wellbeing in a variety of ways. The CAA understands the disturbance that is caused by the regular overflight of aircraft and the impact that aviation noise can have on affected communities.

Government and the aviation industry have worked to try and reduce the impact of noise by promoting the use of quieter aircraft, effective land use planning where possible, restricting the times airports can operate and the routes that can be used and, in some cases, capping the total number of flights that can depart from and arrive into an airport.

Alongside changes to the design of airspace, there are a range of factors that can make a difference to the noise impact of aircraft from any particular airport but over which the CAA has no regulatory control. Examples include changing weather conditions, traffic levels (which impacts where aircraft fly), the types of aircraft used, and variations in the demand for different flight destinations. 

Responsibility for aviation policy and aviation noise matters lies with the Department for Transport. The CAA works closely with the Department for Transport in the development of aviation regulation and policy to limit the environmental effects of aircraft operations where possible.

As designated by the Secretary of State, The Department for Transport is directly involved in measures to improve noise at Heathrow, Gatwick, and Stansted Airports. All other civil aerodrome and aircraft operators are expected to achieve a reasonable balance between their needs and the impact their operations may have upon the local environment.

That means decisions about whether aircraft can operate at night, and how many aircraft are allowed to fly on any given day, etc are generally made by local authorities when they give permission for an airport to be built or expanded.

The CAA requires airspace change sponsor of any permanent change to the published airspace design to follow our airspace change process called CAP 1616. CAP 1616 sets out the steps that must be followed, with CAA approval required at the end of each stage in order for a change sponsor to progress. This is done in accordance with international standards, relevant legislation and government policy. In doing so, the CAA must consider guidance from the Secretary of State on environmental objectives, which includes guidance on aircraft noise impacts.

As it stands, aviation noise, like other mobile noise sources e.g. general road traffic and railway noise, is not a statutory nuisance in the UK, and it is specifically excluded from the Environment Protection Act 1990.

We always keep under review concepts that may inform policy development and where relevant discuss this with the Department for Transport.

For example, the CAA are currently working on an Aviation Noise Attitudes Survey. This is a large-scale social research study, funded by the Department for Transport. The study will provide data on the relationship between aviation noise exposure and an average response to it.

The study began in 2022, and around 46,000 survey responses have been received across two waves of fieldwork in autumn 2023 and spring 2024. The CAA is currently analysing the data with the expectation of publishing results, following peer review, in late 2025 or early 2026.

You can find out more about the Aviation Noise Attitudes Survey on our webpage.

In the meantime, the CAA continues to make airspace change decisions in accordance with the Transport Act 2000, the Civil Aviation Authority (Air Navigation) Directions 2023 and the Air Navigation Guidance 2017.

You can read more about the health impacts of aviation noise and current research on our aviation noise and health webpages.

There are a number of active airspace change proposals (ACPs) in the UK. If you would like to remain informed on any active proposal, you can visit the CAA’s Airspace Change Portal. The Airspace Change Portal contains information on all current ACPs which are being progressed against the requirements of the airspace change process published in CAP 1616. 

The Airspace Change Portal includes a search functionality which allows visitors to provide a postcode/place name to identify any airspace change proposal which are within close proximity to that location and likely to alter traffic patterns below 7,000 feet. You can also search for ACPs by change sponsor organisation. Any ACP must follow our airspace change process, which includes consultation with affected stakeholders, including those potentially impacted by aviation noise.

Changes to the design of UK airspace are proposed by an airspace change sponsor, usually an airport or a provider of air navigation services, including air traffic control. The Airspace Regulation department in the CAA manages the airspace change process and is responsible for determining whether the design of airspace can be changed.

The CAA requires the change sponsor of any permanent change to the published airspace design to follow our airspace change process called CAP 1616. CAP 1616 sets out a number of detailed steps that must be followed. CAA approval is required at the end of each stage in order for a change sponsor to progress to the next stage. This is done in accordance with international standards, relevant legislation and noise and other government policy. In doing so, the CAA must consider guidance from the Secretary of State on environmental objectives, which includes guidance on aviation noise impacts.

Section 70 of the Transport Act 2000 states that after maintaining a high standard of safety in the provision of air traffic services, the CAA must “take account of any guidance on environmental objectives given to the CAA by the Secretary of State after the coming into force of this section” when exercising its air navigation functions (among other factors).

The CAA’s air navigation functions include making decisions on airspace change proposals. The guidance from the Secretary of State on environmental objectives is in the Air Navigation Guidance 2017. While developing and assessing the environmental impacts of airspace change design options, change sponsors must take into account the Air Navigation Guidance 2017, including the Government’s environmental objectives and altitude-based priorities as set out in the guidance.

The environmental objectives with respect to air navigation are designed to minimise the environmental impact of aviation within the context of supporting a strong and sustainable aviation sector. The Government’s key environmental objectives are, in support of sustainable development, to:

1. “limit and, where possible, reduce the number of people in the UK significantly affected by adverse impacts from aircraft noise;
2. ensure that the aviation sector makes a significant and cost-effective contribution towards reducing global emissions; and
3. minimise local air quality emissions and in particular ensure that the UK complies with its international obligations on air quality.”

For the purposes of assessing environmental impacts of airspace change proposals, the Government’s priorities for consideration of the environmental impacts are set out below and must be taken into account during the development, appraisal and discontinuation of all design options assessed during the airspace change process:

“…the CAA should apply the following altitude-based priorities of the Government:

1. in the airspace from the ground to below 4,000 feet, the Government’s environmental priority is to limit and, where possible, reduce the total adverse effects on people;
2. where options for route design from the ground to below 4,000 feet are similar in terms of the number of people affected by total adverse noise effects, preference should be given to that option which is most consistent with existing published airspace arrangements;
3. in the airspace at or above 4,000 feet to below 7,000 feet, the environmental priority should continue to be minimising the impact of aviation noise in a manner consistent with the Government’s overall policy on aviation noise, unless the CAA is satisfied that the evidence presented by the change sponsor demonstrates this would disproportionately increase CO₂ emissions;
4. in the airspace at or above 7,000 feet, the CAA should prioritise the reduction of aircraft CO₂ emissions and the minimising of noise is no longer the priority;
5. where practicable, it is desirable that airspace routes below 7,000 feet should seek to avoid flying over Areas of Outstanding Natural Beauty (AONB) and National Parks; and
6. all changes below 7,000 feet should take into account local circumstances in the development of the airspace design, including the actual height of the ground level being overflown, and should not be agreed to by the CAA before appropriate community engagement has been conducted by the sponsor.”

The Government’s noise policy is “to limit, and, where, possible, reduce the number of people in the UK significantly affected by adverse impacts from aircraft noise”. For the purpose of assessing airspace change proposals, the Government wishes the CAA to interpret this objective to mean that the total adverse effects on people as a result of aviation noise should be limited and, where possible, reduced, rather than the absolute number of people in any particular noise contour.

Adverse effects are considered to be those related to health and quality of life. There is no one threshold at which all individuals are considered to be significantly adversely affected by noise. It is possible to set a Lowest Observed Adverse Effect Level (LOAEL) that is regarded as the point at which adverse effects begin to be seen on a community basis.

As noise exposure increases above this level, so will the likelihood of experiencing an adverse effect. In line with this increase in risk, the proportion of the population likely to be significantly affected can be expected to grow as the noise level increases over the LOAEL. For the purposes of assessing and comparing the noise impacts of airspace changes, the government has set a LOAEL of 51 dB L_Aeq16h for daytime noise and 45 dB L_Aeq8h for nighttime noise.

In addition to assessing effects where noise levels are above the LOAEL, government guidance also sets out supplemental indicators, include the number of aircraft noise events above 65 dB L_Amax during the daytime (N65) and above 60 dB L_Amax during the night-time. 

Consideration and assessment of the potential environmental noise impacts resulting from an airspace change proposal is a necessary part of the CAA’s CAP 1616 decision-making process. It enables people who may be affected by the proposed airspace change to understand the noise impacts of the different design options being considered. For example, from a noise perspective, it may on occasions be better to have multiple concentrated routes that share noise among more people, than a single concentrated route which affects fewer people but to a greater extent.

Rather than a ‘one size fits all’ approach to whether single or multiple routes are better, change sponsors must consider the impacts of different options and decide what will work better in a given situation. These decisions should be informed by considering the anticipated noise impacts, and through engagement with communities.

To achieve this, the CAA requires change sponsors to undertake an environmental assessment that evolves through the options appraisal stages of the airspace change process. CAP 1616 and CAP 1616i Environmental Assessment Requirements and Guidance for Airspace Change Proposals outline for change sponsors the noise metrics and other environmental impacts that need to be considered in the airspace change proposal.

The Air Navigation Guidance 2017 also requires the use of the Department for Transport’s transport analysis guidance (TAG), which is a suite of guidance on how to assess the expected impacts of transport policy proposals and projects. It includes a series of guides and spreadsheet tools based on up-to-date evidence following the principles of HM Treasury’s The Green Book. Therefore, to ensure a consistent and transparent assessment of the options within and across proposals, during the options appraisals of the airspace change proposal process outlined in CAP 1616, airspace change sponsors must monetise the environmental impacts of the airspace change proposed using the TAG: environmental impacts worksheets. The environmental impacts worksheets include an aviation specific noise workbook.

The TAG noise workbook is a tool which assesses the impact of changes in noise exposure. This can be used to assess the impacts of a proposed airspace change compared to the current airspace arrangements. Multiple airspace options can be assessed in this manner.

In terms of noise impacts, adverse effects are considered to be those related to health and quality of life. These adverse effects must be assessed using a risk-based approach above the LOAEL, 51 dB L_Aeq16h daytime and 45 dB L_Aeq8h night-time. Adverse effects of noise are determined through TAG calculated on the basis of changes in LAeq noise exposure.

A monetary value is assigned for the change in the following health impacts: amenity (annoyance), acute myocardial infarction (AMI, commonly referred to as a heart attack), dementia, stroke, and sleep disturbance. Given that annoyance due to noise will be far more common than any of the other health factors (sleep disturbance, AMI, stroke and dementia) it is often the most dominant impact when health and quality of life are assessed.

The output from the TAG noise workbook - aviation forms the primary measure of the noise impact for the purpose of the CAA’s decision-making on an airspace change proposal.

You can read more about how TAG is used in the airspace change proposal process in CAP 1616i.

In January 2021, the CAA published CAP 2091 CAA Policy on Minimum Standards for Noise Modelling. The CAP 2091 policy specifies the minimum acceptable level of sophistication of noise modelling that can be used to provide the CAA with the outputs required for an airspace change proposal.

The sophistication with which the CAA require an airport to model noise depends on the number of people exposed to noise at that airport. The more people exposed, the greater the sophistication that is required to be used. The category of noise modelling required by the CAA is based on the highest category calculated for their 51 dB L_Aeq16h daytime and 45 dB L_Aeq8h night-time contours for the 10-year forecast period (either before or after the proposed airspace change, whichever is greater).

You can read more about the environmental aspects of the airspace change proposal process in CAP 1616i

Changes to the design of UK airspace are proposed by an airspace change sponsor, usually an airport or a provider of air navigation services, including air traffic control. The Airspace Regulation department in the CAA manages the airspace change process and is responsible for determining whether the design of airspace can be changed.

The CAA requires the change sponsor of any permanent change to the published airspace design to follow our airspace change process called CAP 1616. CAP 1616 sets out a number of detailed steps that must be followed, with the CAA approval required at the end of each stage in order for a change sponsor to progress. This is done in accordance with international standards, relevant legislation and government policy. In doing so, the CAA must consider guidance from the Secretary of State on environmental objectives, which includes guidance on aircraft noise impacts.

Consideration and assessment of the potential environmental impacts resulting from an airspace change proposal is a necessary part of the CAA’s CAP 1616 decision-making process. It enables people who may be affected by the proposed airspace change to understand the environmental impacts of the different design options being considered.

To achieve this, the CAA requires change sponsors to undertake an environmental assessment that evolves through the options appraisal stages of the airspace change process. The options appraisals deliver clear and comparable evidence about a range of factors, so that, for a given proposal, different airspace design options can be compared and assessed on a similar basis.

Change sponsors are required to include environmental impacts in their options appraisals, through which the potential costs/benefits that may arise within the context of an airspace change can be assessed.

The requirements for an environmental assessment include a number of specific metrics that must be used in order to derive a quantitative output, as set out in CAP 1616i. In terms of environmental impacts, these metrics include noise, greenhouse gas emissions (expressed as CO₂e), local air quality, tranquillity and biodiversity.

During the options appraisals, change sponsors must monetise certain environmental impacts of the airspace change using the TAG: environmental impacts worksheets. The environmental impacts are monetised as an annual cost over the 10-year appraisal period and the output is the net present value of the change in noise exposure/greenhouse gas emissions/local air quality emissions.

The requirements for the environmental assessment are scalable and proportionate, primarily determined by the characteristics of the airspace change and potential impacts, which is in part based on the altitude and location in which the airspace changes occur.

TAG is the Department for Transport’s suite of guidance on how to assess the expected impacts of transport policy proposals and projects. It includes a series of guides and spreadsheet tools based on up-to-date evidence following the principles of HM Treasury’s The Green Book.

During the options appraisals of the airspace change proposal process outlined in CAP 1616, airspace change sponsors must monetise the environmental impacts of the airspace change proposed using the TAG: environmental impacts worksheets. The environmental impacts worksheets include an aviation specific noise workbook.

The TAG noise workbook is a tool which assesses the impact of changes in noise exposure. This can be used to assess the impacts of a proposed airspace change compared to the current airspace arrangements. Multiple airspace options can be assessed in this manner.

In terms of noise impacts, adverse effects are considered to be those related to health and quality of life. These adverse effects must be assessed using a risk-based approach above the lowest observed adverse effect level (LOAEL), 51 dB L_Aeq16h daytime and 45 dB L_Aeq8h nighttime. Adverse effects of noise are determined through TAG calculated on the basis of changes in LAeq noise exposure.

The Department for Transport has produced a Guide to WebTAG Noise Appraisals for non-experts which provides an overview of TAG noise appraisals.

A monetary value is assigned for the change in the following health impacts: amenity (annoyance), acute myocardial infarction (AMI, commonly referred to as a heart attack), dementia, stroke, and sleep disturbance. Given that annoyance due to noise will be far more common than any of the other health factors (sleep disturbance, AMI, stroke and dementia) it is often the most dominant impact when health and quality of life are assessed.

The output from the TAG noise workbook - aviation forms the primary measure of the noise impact for the purpose of the CAA’s decision-making on an airspace change proposal.

Changes to CO₂ impacts must be included in the options appraisal process. The impacts of greenhouse gas emissions are monetised as an annual cost over the 10-year appraisal period and the output is the net present value of the change in greenhouse emissions.

Changes to local air quality impacts are included in the options appraisal process as well, with TAG providing guidance on the assessment of a monetised value based on the change in volume of local emissions if any breaches of statutory air quality limits are anticipated.

More information on using these tools is given in TAG unit A3 environmental impacts, TAG unit A5-2 aviation appraisal and in Annex C of the Air Navigation Guidance 2017.

You can read more about how TAG is used in the airspace change proposal process in CAP 1616i.

As part of ‘Stage 5 – Decide’ in the CAP 1616 airspace change proposal process, the CAA may publish an environmental statement as part of our decision-making documents.

In making our decision, the CAA will state whether it approves or rejects the final airspace change proposal, with clear assessments of individual factors and an explanation about how we have reached our decision, including weighing the different factors involved.

The CAA’s decision is made in the context of a number of legal duties and, where applicable, government policy. Our duties highlight the factors we must consider before making our decision, and these include:

• in line with the Air Navigation Directions 2023, ensuring the change is in accordance with the Airspace Modernisation Strategy, as well as the CAA’s published procedures and policy on the design and classification of UK airspace, such as this airspace change process
• consideration of the airspace change proposal against the statutory factors in section 70 of the Transport Act 2000, including safety, security, and operational and environmental impacts
• consideration of any other relevant requirements of government policy and legislation, including where relevant the Conservation of Habitats and Species Regulations 2017.

Output from regulatory decision (CAA and/or Department for Transport)

Decision documents including (possibly):

• a decision statement
• CAA final options appraisal assessment
• CAA safety review (plain English summary)
• CAA operational assessment
• CAA consultation assessment
• CAA environmental statement
• CAA decision log (explanation of how we reached our decision and required conditions/modifications).

We recognise the disturbance caused by the regular overflight of air traffic and the impact aviation noise can have on affected communities.

The CAA are working hard to encourage the aviation industry to reduce its environmental impact; aircraft are much quieter than they were just 10 years ago, and the noisiest aircraft are banned from many UK airports.

The CAA has the opportunity to contribute to the government’s aim of reducing the environmental impacts of aviation by seeking to promote the most efficient use of airspace and the expeditious flow of air traffic. This includes procedures that enable aircraft to climb efficiently, allow direct routings, reduce holding times and facilitate the consistent use of continuous descent and low power/low drag procedures.

The use of Continuous Climb Operations (CCO) has implications for both noise and CO₂/fuel efficiency. CCO is considered to have an overall neutral impact on noise, but it does involve the redistribution of some noise. CCO has the potential to reduce fuel burn as aircraft reach efficient cruising levels earlier leading to fuel savings and a reduction in the amount of emissions, including CO₂. CCO also means aircraft get above some of the most complex and congested low level airspace more quickly. Once clear of these areas there is generally more opportunity for aircraft to be routed directly onto their chosen path and save flying time, track miles, creating more efficient aircraft operations.

The government would like to see CCO introduced across the UK over the coming years as part of the overall modernisation of the UK airspace network. CCO is a key  component of the Airspace Modernisation Strategy and the Airspace Change Masterplan. The CAA is encouraged to continue to work with the aviation community to introduce CCO more widely.

When a procedure for a Continuous Descent Operation (CDO) is flown the aircraft stays higher for longer (in comparison to a conventional approach), descending continuously from the bottom of the stack (or higher if possible). Being higher for longer and using less engine thrust means the noise impact on the ground is reduced (up to 5 decibels) in locations 10– 25 nautical miles from the airport and directly under the approach path. The use of CDO procedures can also mean fuel savings and reduced emissions since less engine power is required.

Consideration should therefore be given to how the use of CDO and low power/low drag procedures can be promoted when developing new procedures and when considering proposals for changes to existing airspace arrangements. Both procedures should be regarded as best practice for use at all airports where local circumstances (such as terrain clearance) do not preclude it.

Improvements in aircraft track-keeping and precision Performance Based Navigation (PBN) enhances navigational accuracy offering key environmental benefits by creating more predictable and efficient aircraft operations leading to reduced costs, flying time and emissions.

Improved track-keeping and PBN allows aircraft to closely adhere to predefined flight paths, ensuring they consistently fly the same routes. Traditional navigation systems, which rely on ground-based beacons, often lead to deviations in flight paths due to lack of precision. In contrast, PBN ensures that aircraft remain within narrow corridors in the sky. This accuracy reduces the variability in flight paths and minimises the spread of noise. This can help to concentrate the impact over specific, and sometimes less populated, areas. As a result, fewer people might be affected by aircraft noise, as it avoids dispersal over urban or residential zones.

The high accuracy of PBN can be utilised to either concentrate flights over areas that are less sensitive to noise—such as industrial or sparsely populated regions—or to create multiple flight paths for alternate usage. This alternation provides noise respite for communities. For example, by designing airspace with multiple routes, aircraft can switch between them on a rotating basis, allowing predictable breaks from noise for residents living under the flight paths. Additionally, the predictability of PBN helps residents anticipate when noise will occur, which can mitigate its health impact and enhance tranquillity.

PBN also facilitates the design of routes that avoid flying over densely populated areas altogether. With the improved accuracy provided by satellite-based navigation, airspace designers can create paths that steer aircraft around towns, cities, or noise-sensitive zones. Such flexibility was not possible with conventional navigation methods that relied on the placement of ground-based navigational aids. By diverting flights over less populated regions, the overall number of people affected by noise is reduced.

Airspace designers have greater freedom to tailor routes to meet both operational and environmental goals. They can design routes that minimise overflight over sensitive areas or provide predictable relief by alternating routes. This flexibility allows regulators and designers to consider safety and efficiency alongside environmental impacts, such as noise. For instance, noise abatement procedures can be implemented by directing flights to follow PBN routes during specific hours, helping to mitigate noise during sensitive times, like nighttime.

During the arrival phase, PBN enables aircraft to follow more stabilised approaches, maintaining Continuous Descent Operations (CDO) where aircraft descend steadily rather than using a stepped approach. This method reduces the need for engines to throttle up and down, which is a major source of noise during approaches. Similarly, PBN allows for more precise routing on departure, enabling aircraft to climb steadily and quickly away from noise-sensitive areas, thus reducing noise exposure for those living near airports.