The United Kingdom’s (UK) government undertakes periodic reviews of the UK transport strategy, including aviation.

The government’s current aim is to develop an aviation strategy to support the industry in delivering improvements for passengers, the environment, and the country. The new strategy will set out the long-term direction for aviation policy to 2050 and beyond.

In 2018, the UK Department for Transport (DfT) published a call for evidence, Beyond the Horizon, The Future of UK Aviation – Next steps towards and Aviation Strategy, summarising all the areas that the new strategy needs to consider, including noise issues experienced by communities. The UK CAA’s Environmental Research and Consulting Department (ERCD) was requested to calculate future noise exposure estimates to form part of the consultation document for the aviation strategy.

The Department for Transport commissioned the UK CAA to undertake noise limit and noise forecast analyses in support of the strategy.

The ERCD were required to calculate forecast noise exposure for 2025, 2030, 2040 and 2050 for eight UK airports under two traffic growth assumptions. The two scenarios were considered to identify the effect of imposing different limits on traffic growth, to understand the implications and opportunities for reducing noise through increasing the rate of fleet replacement and increasing the rate of technological improvement.

DfT wanted to gain insight into how to meet its policy objective to limit and, where possible, reduce the number of people in the UK who are significantly affected by aircraft noise. For this, calculations with and without population growth were required.

The team was tasked to provide noise modelling results for 70 separate scenarios, each with multiple metrics. These included the areas, populations, number of households and noise sensitive amenities within the contours. The calculations had to be accurate as miscalculations could affect policy decisions resulting from the new aviation strategy, which could have significant and lasting consequences.

The content of the analysis design had to be impartial, so DfT’s specialist traffic forecasting consultancy provided traffic volume data. The sponsor organisations provided the route design information for each traffic growth assumption. ERCD used its expertise to create data to model new, quieter aircraft designs that reflect future scenarios.

Alongside the usual noise exposure contours, supplementary noise metrics were used to quantify noise emissions generated by aircraft movements at night time and noise impacts (numbers of people highly annoyed during an annual average 24-hour day, and numbers of people highly sleep-disturbed during the annual average 8-hour night). The ERCD evaluated the correlation between noise emissions, noise exposure and noise impacts.

To ensure accuracy, ERCD established working practices and common modelling assumptions, including average temperature, atmospheric pressures, and ground types. It also implemented rigorous quality assurance procedures.

ERCD produced results for 70 separate scenarios, each assessed using multiple noise metrics, requiring over 2,800 individual model runs. Results for a baseline year were calculated for comparative purposes.

The team undertook analysis to design a limit scheme containing the following:1) Nationally set absolute limits based on Quota Count¹ or noise contour area across major UK airports; 2) Locally set absolute limits on Quota Count or noise contour area for each airport; 3) Local monitoring of daytime and night-time noise impacts; 4) Reporting requirements.

ERCD published the CAP1731 report, which presented a feasibility study of implementing airport noise limits nationally and locally, including the pros and cons that noise limits may create. It identified the noise level in the shorter/medium term (2025) and in 2030, 2040, and 2050. The report also included two sensitivity analyses to understand the impact of older aircraft being retired and replaced by newer types faster and whether the rate of technology improvement was faster than anticipated.

1 Quota Count is a classification system based on aircraft noise certification levels which is designed to indicate the contributions individual aircraft make to the total noise impact around an airport.