Method and sources

This site estimates aircraft noise across London and the Thames Valley today and with the proposed third runway. The method, assumptions and data sources are set out below so that anyone can check them.

What is and is not known

The third runway's flight paths have not been designed. Airspace will be designed through the Civil Aviation Authority's airspace change process after planning decisions. The paths shown here are generic: straight-in arrivals on a 3° glideslope and departures that fan out after 5 km. They show the general pattern of exposure, not where specific routes will go. They will be updated with the indicative designs in Heathrow's consultation (27 October to 22 December 2026).

Noise model

Runways. Existing runway thresholds from the UK Aeronautical Information Publication. The proposed north-west runway is 3,500 m long, parallel to and 1,035 m north of the northern runway (Heathrow 2019 Preferred Masterplan); its exact position is approximate.
Traffic. Today: the 480,000 annual movement cap (about 1,315 a day). With third runway: 756,000 a year (about 2,071 a day), Heathrow's 2025 proposal. Arrivals and departures are split equally across runways, with 70% of operations in westerly winds.
Sound. Each flight contributes a sound exposure level that falls with slant distance, using fleet-average values for a 60% narrowbody / 40% widebody mix. Flights are spread sideways around each path to reflect real dispersion.
Metrics. LAeq,16h is the average level from 07:00 to 23:00 on an average summer day, the main UK metric for aircraft noise. N65 and N60 count flights per day with a maximum level of at least 65 or 60 dB.
Calibration. One offset is applied to all levels so that the modelled area exposed to 51 dB or more today matches the 232 km² reported for 2024 in the draft Heathrow Expansion National Policy Statement appraisal. The same offset is used for the third-runway case.

Limitations: no terrain or building screening; a fleet average rather than individual aircraft types; no night-time model. Results are less reliable close to the airport and more than 25 km away. Planned improvements: per-type aircraft noise data from the EASA ANP database, calibration against the full CAA ERCD 2024 contour set, and the consultation's flight paths.

House-value estimates

Studies of house sales compare similar homes exposed to different noise levels. Results are expressed as a percentage change in price per decibel above a threshold. UK evidence is limited: studies around Manchester airport in the 1990s found small effects once the benefits of being near an airport were allowed for. International reviews (Nelson 2004, covering 22 airports; a 2026 US study using a natural experiment) find around 0.5% to 1.0% per dB.

Estimate	Change per dB above 54 dB LAeq,16h	Basis
Low	0.2%	UK (Manchester) evidence
Central	0.6%	Middle of published range
High	1.0%	Upper end of international reviews

The change for a location is this rate multiplied by the increase in decibels above 54 dB between today and the third-runway case. Pound figures use the median price of homes sold in the neighbourhood (ONS Middle Layer Super Output Area, typically 2,000 to 4,000 homes) over the latest 24 months of HM Land Registry sales, never an individual property. Neighbourhoods with fewer than 10 sales are left without a price. Constituency totals add up, for each postcode, the number of households multiplied by the neighbourhood median price and the estimated change. Households per postcode come from Census 2021 counts for each Output Area, shared equally between the residential postcodes in it. Totals cover only the part of each constituency inside the modelled area.

These are illustrative estimates based on statistical averages. They are not a valuation and not financial advice. Actual prices depend on many factors, including wider market conditions, transport links and compensation. Homes inside Heathrow's compulsory purchase and property offer zones are eligible for market value plus 25%.

Time each day with aircraft above 65 dB

This is how long, on a typical day, you would hear at least one aircraft louder than 65 dB. It is shown for each postcode, for each constituency, and in the 24-hour strip of the results.

Why 65 dB: an aircraft peaking at 65 dB or more interrupts normal conversation and is clearly heard indoors with a window open. The count of such events (N65) is a supplementary measure used by the Civil Aviation Authority and airports, because averages such as LAeq,16h do not show how often noise intrudes.
How it is counted: the day is split into 288 five-minute periods. A period counts if at least one aircraft is expected to peak above 65 dB at that location. The figure is the total time across those periods. One aircraft in a period therefore counts as five minutes, so the measure describes how much of the day is disturbed, not how long each aircraft is heard.
Typical day: flights in each period come from the schedule described below, with the 40% widebody and 60% narrowbody fleet mix and a small spread in each aircraft's level. The figure is the average over many such days, so it does not change from one visit to the next. It assumes westerly wind (about 70% of days) and the week 1 runway pattern; the 5-minute chart lets you switch to easterly wind and week 2.
Constituency figure: the average across all homes in the constituency that lie inside the modelled area, weighting each postcode by its number of households (Census 2021).
Limits: it uses the same generic third-runway flight paths and calibrated noise model as the rest of the site, so it will change when the consultation's routes are added. Night flights are included as currently scheduled.

Loud flights before 07:00 is the expected number of flights between midnight and 07:00 that peak above 65 dB at the location, on the same typical day. Most fall between 04:30 and 07:00, when the first scheduled arrivals land and early departures leave; this is the period of the day when sleep is most often disturbed.

Noise through the day

The average level (LAeq,16h) spreads all the noise of a day evenly over 16 hours. What people hear is a series of individual aircraft, busier and quieter periods, and breaks when a runway switches from arrivals to departures. The daily chart for each postcode shows this by simulating one typical day in 5-minute steps.

Flights: today 1,315 a day. About 16 arrive between 04:30 and 06:00, the rest are spread evenly from 06:00 to 23:00, and a few run until 23:30. With a third runway, 2,071 a day, with a 6.5-hour night ban (taken here as 23:00 to 05:30; the hours are not yet decided).
Runway pattern today: one runway takes arrivals until 15:00 and the other after 15:00, swapping each week, with departures on the other runway. This follows Heathrow's published runway alternation in westerly winds, simplified.
Runway pattern with a third runway: the three runways rotate between arrivals, departures and mixed use across three periods of the day. This is an assumption; the actual pattern will be set through the airspace design and consultation.
Each flight: the number in each 5 minutes is drawn at random around the schedule. 40% are widebody aircraft, about 5 dB louder at their peak than narrowbodies, with a small random variation. Levels come from the same calibrated model as the map.
Background: 45 dB by day and 38 dB at night without aircraft, typical of a residential street. Actual background varies, especially near main roads.

Data sources

Draft Heathrow Expansion National Policy Statement, Appraisal of Sustainability noise annex (Department for Transport, June 2026). Crown copyright, Open Government Licence.
CAA Environmental Research and Consultancy Department, Heathrow noise contours 2024 (ERCD Report 2501).
UK Aeronautical Information Publication, EGLL aerodrome data (NATS).
Heathrow 2019 Preferred Masterplan and Airspace and Future Operations consultation.
ONS Postcode Directory (August 2026); Census 2021 households by Output Area (TS041); ONS constituency names and codes (July 2024). Source: Office for National Statistics licensed under the Open Government Licence v3.0. Contains OS data © Crown copyright and database right 2026; contains Royal Mail data © Royal Mail copyright and database right 2026.
Members of Parliament: UK Parliament Members API, Open Parliament Licence.