This has already been discussed here:
http://www.fsdreamteam.com/forum/index.php?topic=1377.0There are some suggestion there you might try to ease the issue.
As I've said there, I only have very minor stutterings for a 1/10th of a second, which really don't distract at all from the flight. Depending on the system configuration and other addon installed in the area (like a terrain addon), this might be more of a problem of not, please read all the thread there.
I have checked that and I have a lot of more huge and complicated airport like EDDF, LFPG, EGGL which runs perfectly
Apart for the fact that is not true this airports are "a lot more huge and complicated", considering the installer size for EGLL it's 30% smaller than LSGG, mostly because of the high number of hi-res textures we have in LSGG, which can also be a reson why it performs flawlessly in FSX, which has a much better texture loading mechanism that doesn't gobble the machine, creating stuttering.
These are all sceneries which contains a lot of FS9 code and, because of this, they perform worse than our sceneries in FSX (there's a comparison thread here about fps in JFK FSX compared to EGLL in FSX). Since we design and optimize the scenery with FSX in mind and, more specifically, with FSX-capable hardware in mind, it likely that it wouldn't perform so well in FS9.
Which is something that FS9 users should accept (just like FSX users are accustomed to expect sub-par performances from FS9 ports), because we always were very open about the fact that we only design with FSX in mind and the FS9 version is just a port. And, we have a Trial version, which is there also for this reason.