Can someone explain why Boris Island would solve the noise problem, which appears to be Boris's chief concern about Heathrow?
The various Thames Estuary sites are a bit further east of London than Heathrow is west, but not much.....
As you point out, "Boris Island" has become a euphemism for several proposed sites in the Thames Estuary, ranging from two different off-shore island sites (the actual "Boris Island" proposals), to the Isle of Grain site proposed by the Sir Norman Foster Group, which latterly gained the support of the Mayor of London, replacing his own support for the "Boris Island" idea.
....In either case an east-west runway orientation means that planes will fly over central London, but in the case of Boris Island they will more often be taking off and therefore making more noise, as the wind is more often westerly.
It would actually be the reverse effect on London itself.
The routes that departing aircraft follow immediately after take-off, are more widely dispersed than the final approach path to a runway, which is usually the extended centreline of the landing runway.
The reasons for the different departure routes are that aircraft are heading out in different directions towards their various destinations and that dispersion allows far more departure movements to take place off the runway than could be accommodated if the aircraft were all following the same route.
The departing aircraft follow set Standard instrument Departure routes, which also incorporate Noise Preferential Routes for the first few miles until the aircraft are above a specified minimum altitude. These various departure routes feed into the en-route airway/air route structure.
Discounting the proposed off-shore sites and looking at the more realistic IOG proposal...
With the more common westerly (wind) orientation, the various departure routes from the IOG site could and would be arranged to avoid most of London, both geographically and below a certain altitude overhead. Certainly, central London would not see any aircraft overhead at the altitudes currently experienced with aircraft either landing or taking-off from Heathrow.
The eastern fringes (east of the M25 and the outlying areas to east and SE) of London would however be affected and it's likely much traffic would be routed over outer south London.
What would be unavoidable, is that a whole swathe of towns and built-up areas in SW Essex (north of the Thames corridor) and a number of more separated towns and settlements south of the river, would be affected by noise from those departing aircraft.
A mitigating factor, is that with new airspace arrangements designed for such a new airport, faster, less constrained climb profiles for departing aircraft could be accommodated, thus reducing the size of the area most affected by aircraft noise.
In the case of the less common easterly operations, we see a very different scenario.
Note that the IOG proposal, as with all the green field proposals, is for a 4 runway airport.
The likely mode of operation will be the simultaneous use two runways for arrivals and two for departures.
This will mean parallel approach paths to the two landing runways, resulting in a wide swathe of E and SE London and the Thames corridor (from just east of a line roughly from Barking to Sidcup, outwards towards the IOG) being underneath or in affected areas either side of the centrelines of the proposed runways.
Not only that, aircraft will also have to be fed into those approach paths and will therefore be flying low over SW Essex and NW Kent.
For guidance..... although the easterly orientation accounts for just over 30% of operations at Heathrow, that is still a significant proportion of time and number of aircraft movements.
The easterly operations also predominate at varying times of the year, due to the weather.
For example...
The first 6 months of 2010 - average 44.2% easterly operation (including February 48% and May 54%).
March and April 2011 - 57% & 52% respectively, easterly operation. (set against the average for the first 10 months of 2011 at 30.1%).
April and June 2014 - 45% & 40% respectively.
September and November 2014 - 53% for both.
March and April 2015 - 38% & 47% respectively.
It is often the case that continuos easterly operations lasts for days or even a couple of weeks at a time.
The same is likely to apply to an airport built on the IOG.
Is this idea just a case of moving the noise out of the affluent suburbs of west London and dumping it on the less blessed communities to the east?
Personally, I believe most of the politicians really don't understand the current impacts, let alone the potential impact of a new site.
we deal with these problems on a regular basis you know - civil engineering is fun when it's difficult !