Each airport with over 50,000 movements is required by the European Union to publish a Noise Action Plan every 5 years. Heathrow has just published it latest one covering the years 2019 – 2023. It only focuses on a two-runway Heathrow since, if a third runway gets permission, it will not be up and running until about 2025/6. UK airports will not be required to produce Noise Action Plans if the UK leaves the EU but the Government is considering replacing them with Noise Reduction Plans: https://www.heathrow.com/noise/making-heathrow-quieter/noise-action-plan