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Understanding airspace policy

Last updated: January 2024

Airspace and Operational Changes

What is airspace?

Airspace can be thought of as a country’s aerial territory. As with other countries, international law obliges the UK to provide navigational services in the airspace above it, including air traffic control. For air traffic control purposes, airspace is divided into two main categories: controlled, and uncontrolled.

Controlled airspace can also be divided into two main categories: 1) the network of airways or “corridors” linking the airspace (Terminal Control Areas) above major airports and 2), at a lower level, control zones located around the airports (for more information, click here). Controlled airspace is used predominantly by passenger-carrying airliners and other commercial services, although some blocks are reserved for military use.

Within controlled airspace, all air traffic is known to the air traffic control system, and clearance is needed for aircraft to be operated within it. The design of the network of airspace corridors must be published (in the UK Aeronautical Information publication).

Controlled airspace (CAS) can go from ground level to 66,000 feet. In upper airspace – above 24,500 feet – air traffic control (ATC) is provided by NATS. Below 24,500 feet, which includes the airways and the control zones, ATC is either provided by NATS, or a local provider.

In uncontrolled airspace, aircraft may be flown without air traffic control clearance, and on a “see and avoid” basis (though air traffic control services can be requested). However, pilots must abide by the UK Rules of the Air. Uncontrolled airspace is typically used by light aircraft, including helicopters and balloons, and it can be made available to military aviation.

What are the differences between airspace changes and operational changes?

Airspace changes are alterations made to the published design of the network of airspace corridors and flightpaths operating in controlled airspace. Since airspace changes don’t fall under the Town and Country Planning Act, the airspace change process is not regulated by local authorities. Instead, any proposed changes to airspace are required to adhere to guidance laid out by the Civil Aviation Authority (CAA), the UK’s regulatory body for aviation. Airspace changes can be permanent or temporary, and they are sometimes the result of trials. In each case, the policy requirement is different. This guide deals mainly with permanent airspace changes, where the policy requirements are more lengthy and complex.

Airspace changes can be permanent or temporary, and they are sometimes the result of trials.

Operational changes refer to how those corridors are used, for example, the types of aircraft that fly them, the frequency with which the routes are flown, and the operational procedures used to fly the aircraft (which might differ from airline to airline). Operational changes were not previously overseen by the CAA, but where they lead to planned and permanent redistribution of air traffic (PPR), the CAA now has a regulatory role. Where there is no PPR, rules relating to transparency and engagement apply, but the CAA has no regulatory role. (For more details on PPR, see below).

Airspace Modernisation

Airspace-related policy is set by the UK Government in accordance with international standards and requirements. The UK is one of over 190 members of the International Civil Aviation Organization (ICAO), whose role includes agreeing international standards on the way international airspace is accessed and used. The European Union’s Single European Sky (SES) project, launched in 2004, aims to implement ICAO-agreed airspace standards via a safety and efficiency drive throughout the EU airspace network. Following withdrawal from the European Union, the UK will continue to participate in the scheme. 

A key component of national and international airspace modernisation plans is what is known as “Performance-Based Navigation” (PBN), which is supported by ICAO. PBN will gradually replace a navigation system based on ground-based navigation aids (such as beacons) with one that relies more on equipment on board the aircraft, including satellite-based navigation aids. It is expected that the application of PBN principles will allow aircraft to fly more predictably and accurately.

The biggest changes in the UK are likely to be in the South East, where air traffic volumes are highest.

However, in order to apply PBN principles, the network of flightpaths must be updated. The biggest changes in the UK are likely to be in the South East, where air traffic volumes are highest (some airspace changes have already been trialled in the region).

In recent policy documents on aviation, Flightpath to the Future and the Jet Zero Strategy (both published in 2022), the UK Government was keen to stress that airspace modernisation will be key to delivering “quicker, quieter, and cleaner flights” and more capacity to benefit consumers. 

Note that the Jet Zero Strategy is currently subject to legal challenges in the High Court (on the grounds that the strategy will not enable the Government to meet its legally binding carbon emissions targets by 2050).

The body responsible for maintaining a co-ordinated strategy and plan for the overall modernisation of UK airspace is the Civil Aviation Authority. In January 2023, the CAA published a refreshed version of its Airspace Modernisation Strategy (AMS). You can access the AMS here.

In 2019, the Government decided to proceed with its proposals to give the Secretary of State new powers to enforce the development of airspace change proposals to avoid any hold-ups in delivering the airspace modernisation programme. 

The SoS can delegate enforcement powers to the CAA under Part 1 of the Air Traffic Management and Unmanned Aircraft Act (2021).

Replacing the 2011 Future Airspace Strategy, the AMS sets out the ends, ways and means of modernising UK airspace up to 2040. It also sets out the need for an airspace Masterplan, a detailed plan of interdependent airspace that would show where and when airspace change was needed.

The CAA collaborates with the Department for Transport and the industry partnership Our Future Skies, a group of stakeholders working on different aspects of airspace modernisation. The partnership includes the Airspace Change Organisation Group (ACOG) set up in 2019 by the CAA. Part of ACOG’s role involves producing an Airspace Masterplan.

ACOG has produced two iterations of the Masterplan. A  third iteration was expected in 2023, but has not yet been published. To read more about ACOG’s Masterplan processes and iterations, click here.

The Air Navigation Guidance

While the Transport Act requires the CAA to take account of the DfT’s environmental objectives, its priority is to maintain a high level of safety.

With safety issues taking precedence, the CAA is required to balance several competing requirements, including maintaining an efficient use of airspace, satisfying the requirements of operators and owners of aircraft, and the environmental objectives.

However, as AEF has argued, there is a widely held perception amongst communities that the CAA fails to balance the interests of all parties, as required, and sees its primary duty as facilitating aviation growth. As long as the CAA continues to do this, it’s difficult to see how it can make impartial judgments about airspace changes.

In preparation for an airspace modernisation programme, and in response to strong community opposition to some early airspace trials, the Government launched a major airspace change consultation in February 2017. In light of its consultation, the Secretary of State for Transport issued new policy guidance in October 2017 – the Air Navigation Guidance (ANG). The main objectives and requirements of the ANG are set out below.

Environmental Objectives

The Department for Transport’s ANG provides guidance to the CAA under section 70(2) of the Transport Act 2000, which requires the CAA to “take account of” the Government’s environmental objectives when carrying out its air navigation functions. These air navigational functions include approving changes to the UK’s airspace design. Accordingly, the ANG sets out the CAA’s duties regarding three environmental objectives, including noise (with the aviation industry also expected to take account of the ANG). The DfT’s guidance is incorporated into CAP1616, the CAA’s airspace change policy. A full list of documents relating to the requirements and guidance around proposed airspace changes can be found here. (Note that the environmental objectives do not apply to the CAA’s power to reclassify airspace).

The three main environmental objectives set out in the ANG are to:

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

However, while the ANG requires the environmental impacts of aviation to be mitigated, it simultaneously seeks to ensure aviation continues “to make its important contribution to the UK economy”. So while the environmental impacts of aviation must be mitigated, mitigation can be done only to the extent that it’s “practicable and realistic to do so”. As the ANG puts it, the environmental objectives “are designed to minimize the environmental impact of aviation within the context of supporting a strong and sustainable aviation sector”. This looks like trying to have it both ways.

With this in mind, it’s worth looking at the wording and policy context of the ANG’s noise objective in detail.

The noise objective is to:

limit and, where possible, reduce the number of people in the UK significantly affected by adverse impacts from aircraft noise.

At first glance, the statement might seem very strong. But while it commits to limiting the number of people affected by aircraft noise, the number of impacted people will be reduced only “where possible”. (Indeed, the ANG concedes that there will be situations where it might be best to expose more people to aircraft noise, if to a lesser extent).

While the noise objective commits to limiting the number of people affected by aircraft noise, the number of impacted people will be reduced only “where possible”

The statement also prompts the question: what does the Government mean by “limit”, “reduce” and “significantly”? The ANG offers no definitions of these terms, and no noise reduction targets are set, making it tricky to determine whether the policy objective has been met. The justification for the absence of noise reduction targets is that there’s “no one threshold at which all individuals are considered to be significantly adversely affected by noise.” In other words, people react differently to different noise levels.

Rather than focusing on thresholds, the Government therefore requires airspace change sponsors to assess all noise above the Lowest Observed Adverse Effect Level (LOAEL). The LOAEL is defined as the threshold “at which adverse effects begin to be seen on a community basis”, and there is one LOAEL for daytime, and another for night (see below). As noise exposure increases above these LOAELs, the likelihood of experiencing an adverse effect (such as heart disease or depression) will also increase – and so will the number of people adversely affected.

The main problem with this argument is that the World Health Organisation (WHO) has identified and recommended clear and long-term noise reduction targets (see below). In choosing not to follow suit, the Government’s environmental noise objective appears designed to avoid getting in the way of its wish to see a growth in aviation capacity.

As for the LOAELs themselves, a set of assumptions about aircraft altitude informs the way that the noise objective policy is applied. In short, the CAA is required to take into account “altitude-based priorities”. These are set out in the box below.

Permanent Airspace changes: Altitude-based environmental priorities

  • From the ground to below 4000 feet, the priority is to limit and, where possible, reduce the number of people affected by aircraft noise
  • 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 the option that’s the closest to the existing published airspace design
  • Above 4000 feet to below 7000 feet, the priority is to limit and, where possible, reduce the number of people affected by aircraft noise – unless the airspace change sponsor can demonstrate that this would disproportionately increase CO2 emissions
  • Above 7000 feet, the priority is to reduce aircraft CO2 emissions
  • Where practicable it is desirable that air space routes below 7,000 feet should seek to avoid flying over Areas of Outstanding Natural Beauty (AONBs) and National Parks

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 altitude-based priorities are based on the Government’s assumption that below 4,000 feet there is a “strong likelihood” that aircraft could create levels of noise exposure above the LOAELs for day and night time. However, above 4,000 feet, this is felt to be “unlikely”. If this is the case, it’s rather puzzling that the noise objective is still prioritised between 4000 and 7000 feet, albeit with a proviso about CO2 emissions. In fact, while the Government prioritises CO2 emissions over noise above 7000 feet, some of our members have argued that even the 7000 feet cut-off is too low, and that a cut-off level of 10,000 feet would be more reasonable.

Indeed, the list of altitude-based priorities itself includes two references to situations where prioritising CO2 emissions over noise might not always be appropriate above 7000 feet. The first reference is to National Parks and Areas of Outstanding Natural Beauty. The second is to “local circumstances”, including the height of ground levels beneath proposed flightpaths.

The environmental noise objective puts National Parks and AONBs at risk of aircraft noise pollution

Looking at the issue of National Parks and AONBs, it seems likely that the environmental noise objective puts these areas at risk of aircraft noise pollution. The objective is to reduce the total adverse effects on people, meaning that airliners should usually be directed away from densely populated urban areas. As a consequence, more sparsely populated areas, typically having low ambient noise, could possibly take the hit. This includes rural areas that are not National Parks or AONBs, but that are nevertheless cherished by locals and visitors.

The ANG makes no mention of “ordinary” countryside, but it does recognise the implications for tranquillity in National Parks and AONBs. However, in recognising these implications, the ANG states that the statutory purpose of National Parks and AONBs is to ensure only that their landscapes and beauty – not their tranquillity – is protected:

The statutory purpose of National Parks is to conserve and enhance their natural beauty, wildlife, and cultural heritage and to promote opportunities for the understanding and enjoyment of their special qualities by the public. The statutory purpose of AONB is to conserve and enhance the natural beauty of their area.

What is meant by “natural beauty”?

Natural England is clear that AONB’s “natural beauty” criteria include “relative tranquillity, where natural sounds, such as streams or birdsong are predominant”.

While it’s correct that the National Parks and Access to the Countryside Act (1949) makes no reference to tranquillity, Natural England’s response to the Airports Commission’s Aviation Noise Discussion Paper stated:

“Tranquillity is an essential element of many of our nationally protected landscapes, one that makes a significant contribution to people’s experience and enjoyment of these landscapes.”

Despite its narrow interpretation of the statutory purpose of National Parks and AONBs, the ANG makes some attempt to address the tranquillity issue, albeit in a heavily caveated way: where practical, it’s desirable that airspace routes below 7,000 feet should seek to avoid flying over AONBs and National Parks. Sponsors, meanwhile, are required only to take this into consideration.

The Government’s noise policy ignores the importance of National Parks and AONBs as living and working spaces that are also well-used visitor attractions providing crucial health and wellbeing benefits while contributing significantly to local economies.

As just one example, 37,000 people live within the Surrey Hills AONB and 1.5 million live within 10km of it. According to its website, millions of people visit the AONB each year. 

However, if AONBs and National Parks are avoided, thousands of people enjoying and living in “ordinary” countryside might be expected to bear the brunt of aviation noise instead.

AEF believes that no one’s life should be blighted by aircraft noise, whether they live in an urban environment, or in a rural one. The answer is to reduce noise, not merely to move it around.

Turning to the issue of local circumstances and the noise objective, it’s encouraging that the ANG recognises that the UK is not uniformly flat. But while recognising that prioritising CO2  emissions under altitudes of 7,000 feet is a problem over hilly areas, the ANG directs the CAA only to ensure that the industry “takes account” of this when developing airspace change proposals. The policy offers no clearer direction than that. Meanwhile, “appropriate community engagement” is not as empowering as it might perhaps seem. (See below).

The answer is to reduce noise, not merely to move it around.

The ANG, then, attempts to have it both ways. It seeks to facilitate aviation growth on the one hand while aspiring to sustainability on the other. It stresses the importance of reducing the number of people adversely affected by aviation noise, yet does not commit to noise reduction targets. As a consequence, the DfT’s noise objective is vague and hard to use as a meaningful standard.

Nevertheless, the ANG’s policy changes brought about some welcome community gains, and these are explored below.

Stakeholder engagement and transparency

The ANG introduced new requirements around stakeholder engagement. Where permanent airspace changes are proposed, the sponsor (the organisation seeking airspace change, usually an airport) is expected to engage with the public at an earlier stage than previously – at the design stage, and during an initial options appraisal (see below).

In the design stage, the change sponsor is expected to draw up airspace change design principles through discussions with, for example, community representatives and local community groups, Airport Consultative Committees, and representatives of General Aviation clubs or groups. If it wishes, the change sponsor can convene a focus group for the purposes of discussion. Discussion should include any issues of altitudes or height of local terrain, and special features of the area, and the results of consultation should be submitted to the CAA.

Following these early discussions, a set of design options are identified and compared against a baseline scenario (discussed below). The baseline scenarios and design options are then shared with the same stakeholders that were consulted at the design stage. These early consultations are meant to identify and prevent any conflict arising later in the process. A full and extensive consultation exercise takes place at a later stage.

In addition to early-stage consultation, the process also places more emphasis on transparency than previously. In recognition of this, the CAA set up an online portal where details of an airspace change proposal can be found, comments can be made, and progress can be tracked. The emphasis on engagement and transparency also extends to operational changes (See below).

In addition, the DfT has formed an Airspace and Noise Engagement Group (ANEG). The group brings together representatives from local authorities, community and environmental groups, airports, airlines, air navigation service providers and sectoral bodies. The intention is for ANEG to act as “a sounding board to identify, discuss and, where possible, resolve airspace and airport noise issues that impact on the work of the department”.

AEF is broadly supportive of enhancements to transparency and engagement processes within airspace change policy. But while the ANG places greater emphasis on community engagement and transparency, the assumption in favour of aviation growth suggests that consultations will really be about deciding where aviation noise is “best distributed”. 


In practice, it appears the consultations will involve stakeholders identifying the least bad option locally and consequently risk dividing communities by creating winners and losers.

In addition, offering “appropriate community engagement” is a slippery phrase. Ultimately, it’s the CAA that decides on the kind of engagement that’s appropriate. And, even assuming that people will have the time to absorb lengthy consultation and policy documents, the kind of questions asked can constrain the responses received.

The Secretary of State Call-In Power (on proposed permanent changes to airspace design)

Prior to the ANG 2017, decisions on permanent airspace change proposals were made solely by the CAA. Current policy is that they can be “called in”, meaning that the final decision would rest with the Secretary of State for Transport, rather than the CAA.

Anyone can ask for the SofS to call in a proposal to permanently change the design of UK airspace (including the airspace change sponsor). A request must be made in writing either to the CAA, which must then notify the Transport Secretary, or to the Transport Secretary directly. However, there is only a small window in which to make a written call-in request – within four weeks following the airspace change sponsor submitting its proposal to the CAA. In addition, the CAA requires that all call-in requests be made using its online portal. 

Having been notified of the request, the Transport Secretary must be satisfied that any one of three criteria has been met. The third criterion refers to noise impacts, and it is the only environmental criterion.

The proposed airspace change can only be called in if it:

  • is of strategic national importance or,
  • could have a significant impact (positive or negative) on the economic growth of the United Kingdom, or
  • could both lead to a change in noise distribution resulting in a 10,000 net increase in the number of people subjected to a noise level of at least 54 dB LAeq 16hr and have an identified adverse impact on health and quality of life.

A decision on whether to call in a proposal should be made within eight weeks of the proposal being submitted, if possible. If the Transport Secretary decides not to call in a proposal, it’s referred back to the CAA for the final decision. If a proposal is called in, the CAA must provide the Transport Secretary with its “minded-to” decision.

A called-in airspace change proposal is scrutinised by a senior DfT official who looks at evidence presented by the sponsor, and who takes into account the opinion of the CAA, and any other relevant party. The official then makes a recommendation to the Secretary of State on whether the proposal should be approved or rejected, or whether any further work is required (for example, additional stakeholder consultation). The Secretary of State is not obliged to follow the official’s recommendations, or the CAA’s “minded-to” decision, but should take these opinions into account. Once the Secretary of State has made the decision, the DfT should notify the CAA, the sponsor and the requester who initially requested the call-in. (There’s no fixed timetable for handling a called-in proposal, but the DfT aims to make final decisions within three months of the date the CAA provides its opinion, or as soon as is practical).

If the Secretary of State’s decision is either to approve or reject the proposal, the call-in process ends there. If a further work programme is required from the sponsor, once this has been carried out, the proposal goes back to the DfT official for a recommendation. The CAA would be asked for its views on the additional work completed, and whether its “minded-to” opinion had changed in light of it. The official again makes a recommendation to the Secretary of State who then makes the final decision.

AEF believes that a net change of 10,000 in the population newly exposed to noise is too high as a threshold in the noise criterion for call-in, and will exclude changes that will largely affect rural communities.

The airspace change sponsor assesses whether the anticipated noise impact of its proposals will meet the three call-in criteria. The SoS uses the sponsor’s assessment to check and determine the expected noise impact, raising questions about transparency and possible bias.

The Secretary of State is not obliged to call in the airspace change proposal, even if one or all of the three criteria have been met.

The window to make a call-in request is rather small.

Once a final decision to approve or reject a proposal has been made – whether by the CAA or by the Secretary of State – there is no right of appeal.

More information on the call-in process is available here.

Operational changes

AEF is frequently contacted by people expressing concern about suddenly being affected by aircraft noise. The enquirers often tell us that they’ve contacted the airport concerned, only to be advised that no airspace changes have occurred. However, while there might have been no changes made to the airspace design as such, changes have sometimes been made to operational procedures instead.

Cycle paths in the sky are being transformed into motorways overnight

These can include a switch in the types of aircraft being flown, changes to operational procedures (for example, wheels down on approach), or alterations to the frequency of operations. The number of aircraft movements can increase from 10 to 100 a day without this qualifying as an airspace change. 

Previously, the CAA had no regulatory role where operational changes had taken place, and it was difficult, if not impossible, for people to obtain information about operational changes. Policy around operational changes has now changed.

Planned and permanent redistribution of air traffic (PPR)

In 2018, an amendment to the Air Navigation Directive (AND) gave the CAA a new decision-making role where a planned and permanent redistribution of air traffic (PPR) is proposed. A PPR involves a change to written air traffic control procedures, not decisions that are made on a day-to-day basis (such as a response to weather patterns). The decision-making process is triggered when an air navigation service provider (ANSP) identifies that a change to written operational procedures might lead to a “relevant PPR” and notifies the CAA. A relevant PPR is one that meets specified AND criteria. 

The AND criteria

A change to written ATC procedures is a relevant PPR if it:

  • falls within the scope of one or more of Types 1, 2 or 3 


Type 1. Lateral shift in flight track of more than a specified distance 

Type 2. Redistribution between Standard Instrument Departure routes 

Type 3. Change to Instrument Landing System joining point (on approach) 

and 

  • relates to an airport in scope, i.e. which has a Category C or D (or both) approach landing procedure, and/or established Standard Instrument Departure routes published in the UK Aeronautical Information Publication. Click here for further details.

The PPR decision-making process was incorporated into CAA policy in February 2020. It is a shortened version of the policy around changes to the published airspace design, and a proposal cannot be called in by the Secretary of State. AEF was pleased to see the introduction of a CAA decision-making role for certain types of operational changes. However, we were disappointed that the process appears to rely entirely on ANSPs voluntarily bringing PPRs forward to the CAA, based on information that they privately hold, with no comeback if they fail to identify a change that could be a PPR. The CAA has no statutory function to require the ANSP to go through the PPR decision-making process retrospectively if it later transpires that a change, once implemented, subsequently meets the qualifying criteria. It’s difficult to see how an ANSP would feel motivated to go through the process. To read our full response to the CAA’s consultation on PPR policy, please click here.

Operational changes that are not a PPR

Airports are expected to analyse the effects of their operational changes, and they should be transparent with communities about any identified changes to the distribution of traffic. Airports are also expected to consider how noise impacts arising from operational changes might be mitigated.

In addition, where the CAA becomes aware that an airport is withholding information, it can exercise its powers to obtain that information from air traffic service providers – if it deems this necessary.

Accordingly, the CAA’s guidance states that airports should highlight and explain aircraft operational changes to stakeholders retrospectively in published information. Airports should engage regularly with stakeholders in order to discuss information that’s published as well. The CAA also suggests that, in addition to regular community engagement, mitigations should be discussed and considered as part of the airport’s Noise Action Plan, which is updated every five years. While the policy around transparency is a step in the right direction, it’s helpful to keep in mind that airport analysis of operational changes is required only “where practicable”.  Also, the Government was keen that the CAA should maintain a “light touch” approach to operational changes. The CAA’s guidance to airports on this takes the form of best practice, and its role is an advisory one only.

Reclassification of Airspace

In October 2019, the Secretary of State for Transport gave the CAA additional powers to:

  • regularly consider whether airspace classifications should be reviewed;
  • carry out a review (which includes consultation with airspace users) where it considers a change to classification might be made, and 
  • as it considers appropriate, amend any classification in accordance with procedures developed and published by the CAA for making such amendments 

The CAA procedure can be found here.

Changes to aviation noise compensation policy

Rather than limit assistance towards the costs of noise insulation to homes affected by development, where the resultant exposure level is greater than 63dB Leq, provision has now been extended to homes affected by airspace changes. In addition, the Government requires that airspace change sponsors should give consideration to whether compensation might form part of an appropriate package of measures to address the noise impacts of a change.

AEF is broadly supportive of enhancements to transparency and engagement processes within airspace change policy. But while the ANG places greater emphasis on community engagement and transparency, the assumption in favour of aviation growth suggests that consultations will really be about deciding where aviation noise is “best distributed”. 
In practice, it appears the consultations will involve stakeholders identifying the least bad option locally and consequently risk dividing communities by creating winners and losers.

Independent Commission on Civil Aviation Noise (ICCAN)  

The commission was intended to operate as a non-departmental public body of the DfT and was set up in January 2019. Taking its cue from Government, ICCAN’s stated aim was to “improve public confidence and trust in the management of aviation noise”. However, following an independent review of ICCAN’s objectives, functions and outcomes, the Government took the decision to dismantle the Commission in September 2021, concluding that it would be more efficient to absorb its functions into the CAA. While ICCAN’s performance was disappointing, its independence from the Government and the CAA was nevertheless valued by members of the public. The Government created ICCAN because it considered that an independent body was vital to ensure that the views of communities were taken into account by the CAA and industry. It is questionable whether the CAA, which has persistently prioritised the consumer over the environmental impacts of aviation, will be equipped to act independently.

The requirement for options analysis in permanent airspace change proposals

As considered above, sponsors are expected to assess the anticipated environmental impacts of different airspace change options, such as concentrating aircraft along single routes, or dispersing them along multiple ones.

Each option is assessed separately against the change sponsor’s Statement of Need. Importantly, as airspace change processes and implementation take time, CAP1616 specifies that change sponsors must develop baseline scenarios (future scenarios without airspace change) against which design options can be compared. Baseline scenarios are developed both for the year of implementation, and for ten years after implementation.

In developing baseline scenarios, sponsors assume the current-day airspace situation, while also reflecting anticipated changes to the use of airspace independent of proposed changes to its design. These “business as usual” changes to airspace use include fleet changes, any air traffic growth and changes to aircraft types. Wider contexts that are relevant to baseline scenarios include planning permissions and allocations for housing developments that could potentially increase the number of people impacted by airspace change.

The different options are then compared and contrasted to identify the option that best meets the objectives, while limiting environmental impacts as far as practical.

However, the options appraisal has been weakened. We note that the previous version of CAP1616 stated that, at the design stage, doing nothing or doing the minimum “must always be an option unless ruled out on safety or regulatory grounds.” (para 446, here). In the drive to increase capacity via airspace modernisation, this commitment has been dropped.

If engagement is limited to stakeholders having to choose the least bad option locally, many airspace change proposals are likely to be contentious.

The metrics and appraisal guidance to assess noise impacts

Leq is a shorthand way of averaging noise events over a period of time, usually 16hr for day and 8hr for night. So, rather than showing individual or peaks and troughs of noise events, Leq flattens out the events to show a single ‘continuous’ decibel value over the relevant time period.

Airspace change proposals must be accompanied by environmental information showing the likely impacts of the change. Guidance on environmental issues and metrics is provided by the CAA in CAP1616, Appendix B: “Environmental metrics and assessment guidance”.

When carrying out options appraisals (see above), sponsors of permanent airspace change proposals are required to use the DfT’s Transport analysis guidance (TAG) toolkit. TAG is a series of guides and spreadsheet tools for modelling and appraising the impacts of transport projects (mostly around noise, air quality and carbon). In the context of the ANG’s environmental noise objective, TAG measures, in monetary terms, the risks associated with exposure to day and nighttime noise at levels that the DfT believes are consistent with recommendations from the World Health Organisation. So, anticipated impacts will be now mapped above 51 Leq for daytime and 45 Leq at night. Previously, noise thresholds were mapped only at 57 Leq for day and night time.

The ANG states there is currently “no hard evidence showing links between the frequency of noise events and health impacts”. Accordingly, airspace change sponsors aren’t required to take noise event frequency into account for options appraisals.

Nevertheless, to reflect community concerns about noise frequency, TAG will be supplemented by frequency-based noise metrics. If any new evidence arises, it will be incorporated into TAG.

The metrics show that the Government has begun to respond positively to evidence about adverse health impacts at lower noise thresholds. However, the DfT’s lower noise thresholds don’t comply with current WHO environmental noise guidelines. The guidance on aircraft noise “strongly recommends reducing noise levels produced by aircraft below 45 dB Lden., as aircraft noise above this level is associated with adverse health effects.” The guidance also “strongly recommends reducing noise levels produced by aircraft during night time below 40 dB Lnight.” In other words, the metrics and thresholds set by the DfT don’t achieve the overall noise reduction targets which AEF – and communities – would like to see. (The executive summary of the WHO guidance is here.)

Check out our other guides:

Understanding aircraft noise
Understanding aviation-related planning

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