Originally Posted by
DaveReidUK
The first part of the SID is also designated by the Government as the centreline of the Noise Preferential Route (NPR), which airlines are obliged to follow, designed to avoid overflight of built-up areas where possible.
That Finnair was indeed recognised as being "off-track", as can be seen from the highlight on the WebTrak plot:
I don't see what lack of traffic has got to do with not following the NPR.
Well, that’s why I made the point that I didn’t work at EGLL - so I did not have a full appreciation of the NPR requirements there. The SIDS where I did work, EGJJ, were not , as far as I can remember, mandatory as a required route if there was no traffic to separate from. As I remember it, we were at liberty not to use the SIDS should we require it (although, it was probably less hassle to stick with the SIDS - even if they were not strictly necessary). Anyway, thanks for setting me straight. I guess that once the a/c concerned in these instances had gained sufficient altitude so as not to exceed noise requirements, they were able to take a more expeditious route.