Hi Ian,
Which scenery is it that you have installed and where did you get it from? There are often many versions of any particular airport and sometimes there are patches to fix things like this and other times there aren't

I've just checked at
http://walhalla.mine.nu/fs2004.php (the most comprehensive freeware scenery listing there is) and unfortunately there does not appear to be a ready made fix for this airport.
I also looked over at Flightsim.com for any fixes but can't find one...
So, you have three options:- use it as it is with AI aircraft floating around, search the Net for solutions for this problem which was commonplace when FS9 first came out with lots of addon sceneries from FS2002, or you could download a separate AFCAD2 file for the airport, install that over the top of your FS2002 scenery and see if it fixes the issue. If not, remove the scenery and just install the AFCAD2 file and see how the airport looks - at least the other aircraft should be at the same level as you

Sorry I haven't got a better answer - does anyone else have a different solution?