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Respite research

Background

The aviation industry is undergoing a period of significant airspace change, this is mainly due to the Government’s plans to modernise the UK’s airspace over the next few years with the aim to make the airspace much more efficient.

Key to achieving this aim will be the introduction of Performance Based Navigation (PBN) - a form of satellite navigation technology. PBN improves the accuracy of where aircraft fly by moving away from ‘conventional’ navigation using ground-based beacons, to satellite navigation.

PBN is being introduced across the world. This new technology allows more flexible positioning of routes and enables aircraft to fly them more accurately. This helps improve operational performance and reduce delays. However, enabling aircraft to follow an allocated route more precisely will potentially lead to routes becoming narrower and more concentrated than today and we recognise that this concentration of aircraft is a concern to local communities.

What the introduction of PBN does do though, is give the airport greater control over the noise impacts of aircraft. In particular, it gives added impetus to assessing the value to residents of sharing aircraft noise between communities so that, at any given time, some communities experience respite (i.e. airport-managed perceptible relief from aircraft noise).

Whilst we wish to take the opportunity to maximise operational efficiency of how the airport and airspace operates, we recognise the importance of managing the consequences of PBN on local communities in the future.

Respite Working Group

The concept of providing respite from aircraft noise has taken on increasing importance in recent years, as a useful and effective strategy for providing a break from aviation noise. However, there are limited guidelines to explain what respite from aircraft noise means and how it should be implemented.

Heathrow identified a need to improve its understanding of respite from aviation noise and in October 2014 set up a Respite Working Group (RWG) to investigate and advise. The RWG produced a report providing an analysis of the then current state of the art in relation to implementing respite from aircraft noise as part of a noise management strategy, and a proposal for areas of future research.

A review on the state of the art on respite

The RWG concluded that, in order to optimise the delivery of noise respite consistent with efficient operations in the future, Heathrow should commission new research to better understand the key characteristics of an effective respite strategy for the airport and its noise affected communities. Such research would help underpin and inform noise management at Heathrow, rather than provide a specific solution.

Respite Research

Heathrow commissioned Anderson Acoustics to carry out this research. Work commenced in February 2016 and examined two key questions:

  • By how far do you need to spatially change routes (in terms of any resulting differences in sound levels) to make a perceived difference to communities (in terms of discernibility and, ultimately, to be of perceived ‘benefit’)?
  • What are the optimum temporal distribution patterns required? In other words, are quieter periods resulting from managed route alternation more/less beneficial at different times of day; and is alternation of flight-path more/less beneficial than a block of time when one flight- path is used, followed by a block of time when the other flight-path is used?

Researchers used SoundLab to carry out some listening tests during which participants gave feedback on a range of aircraft sounds in terms whether they noticed differences and whether these could potentially lead to a valuable break from the aircraft noise over a longer period of time. A simplified version of the more complex findings suggests that, under active listening conditions in the laboratory, on average:

  • A 2 to 3 dB difference between successive sounds was not particularly noticeable, although over half of the participants thought that it could lead to a more positive view of the airport, compared to providing no difference at all.
  • Differences of 5 to 6 dB between successive sounds may be needed for people to even tell there is a difference.
  • But a difference of at least 7 or 8 decibels may be needed between the average sound level of two sequences of aircraft sounds to provide a valuable break from aircraft noise.

The Respite Working Group’s second question was about how alternating between two routes can be used to provide the most effective respite to the community. This relates to both the time of day and how long two different routes are used. Discussions were held in the community with small groups, during which some recorded aircraft sounds were also played. Participants were asked again about how they valued any differences in sound levels and also about aircraft noise at different times of the day.

The majority of participants preferred quieter periods at either end of the day, both at weekdays and weekends. The most popular route options were for one route for a set period of time, then switching to another. The least popular was to alternate aircraft on each route, one after the other.

These generalised findings - which are based on laboratory type tests - must not be taken out of context though, and for more detailed explanation of the outcomes, please refer to the full written reports.

But it is also recognised that providing effective respite is not just about what we hear – the acoustics - but also about what we see, feel and believe – often referred to as non-acoustic factors and these could be at least as important in the appreciation of respite from aircraft noise. To further explore these factors, follow-on work in the field is being completed.

The above animation has been developed to consolidate and provide an overview of the learning gathered through this journey to improve understanding of the concept of “respite”. It presents the story so far from the formation of the Respite Working Group to the most recently published research work.

This work is also described in the Overview Report which introduces the full Technical Report on the recent laboratory and fieldwork research. This can be found below. The follow-on fieldwork will be reported in due course.