The two animations show views from aircraft making 3.5 degree approaches from the East to a new 3rd runway at Heathrow and a new 2nd runway at Gatwick along these routes. The Heathrow route is taken from Figure 4.4 (Heathrow NWR-R (Respite) Routes) of the Airports Commission’s Noise Local Assessment report, November 2014, and commences 22km from the airport close to the extent of that figure, where aircraft will be at heights of approximately 4,400ft. Similarly the Gatwick route begins 22km from the airport taking a typical route to the extended runway centre line joining from the south.
Arrival Route to a 3rd Runway at Heathrow
Arrivals Route to a Second Runway at Gatwick
Populations flown over have been estimated, using Office of National Statistics population data from 2014, within a swathe centred on the route below. The swathe width is based on work undertaken by the CAA in April 2016 as part of work towards developing consensus on both how far someone would have to be from a flightpath for the reduction in noise to start to become noticeable and also consideration of what constitutes “overflight” (1).
In the analysis undertaken by ERM for Gatwick, a person located at the edge of the swathe seeing an arriving aircraft on the flightpath would be looking up at an approximate angle of 48.5 degrees. The CAA calculates that this is where the noise would be about 3dB quieter than if the aircraft were directly overhead. 3dB is the difference in environmental noise levels that is generally taken to be “just perceptible”
The analysis for the routes shown above indicates that about 280,000 people are overflown at Heathrow in comparison to 3,800 for Gatwick.
(1) Performance-based Navigation; Airspace Design Guidance: Noise mitigation considerations when designing PBN departure and arrival procedures
CAP 1378 April 2016 (UK CAA); Appendix A and B.