Although it depends where you put the point merge. If the 'point' of the point merge is at the latest point of the ILS where aircraft are normally vectored to then you get a spread of approach paths up until that 'point'. Beyond that point aircraft with fly the ILS like they always have.
However, if you place that 'point' miles and miles out then you will get an over-concentration of arrival flightpaths from there to touchdown.
It's hardly rocket science.
RNAV departures are slightly trickier....depends on the mix of routings and the amount of 'flyover' waypoints versus 'flyby' waypoints. By designing in more 'flyby' waypoints you get a bigger spread of departure routes....which is better for folk on the ground (less concentration of flightpaths because each aircraft takes a slightly different path, dependant on speed/weight/type etc.) even for the same RNAV SID.
However, not ideal for ATC in terms of 2 consecutive departures on same SID as each aircraft will fly slight variations on the same SID and therefore departure separation becomes an issue.
It's a good option if you can guarantee an alternation between say northerly and southerly departures all day long.
For the arrivals, if you had to have a point merge miles and miles from the airport (airspace limitations), you'd ideally have at least 2 routes to touchdown from the merge point....offering alternation (or 'relief routes') to residents on the ground.
Not always that simple though to design such structures. But certainly fairer to the communities underneath.
Many thanks for the explanation of point merge. i can see that if the merge point was set 8-10 miles east of LHR for westerlies then the final approach will be very similar to today and no one on that segment will notice. But what about the arc that aircraft must fly down do all arrivals have to fly this in one direction or do you have a path for north arrivals or one for south. Either way it would seem that people further out under the arcs would get a greater concentration of overflights than exists today with the four stacks with different routings to a turn for final and that turn being started anywhere from 6-8 to 12 miles or more out.
Whatever the whole point of my comment was that if the airlines,airport and ATC providers do not work with the affected communities then they will be in for years of grief with objections court cases etc etc.
As regards departures the trial LHR did a couple of years ago meant that pretty much everything headed south or SW with LHR on westerlies was confined to one path toa point just beyond Ascot and then dividing into two one over Bagshot area heading for Midhurst and one passing just north of Camberley heading for SAMPTON and people in the area immediately after the split point got very very angry because traditonally differing performance and differing vectoring split these streams up once again,. With MID departures for example, some would make the turn south over Chobham Common but others would come out as far as Camberley before heading south and people have got used to that ,