The 'fault' you describe is usually because your frame rate is either too low, or your image settings are set too high and the scenery re-writing can't catch up. It is a known issue and you can get the updates from Microsoft which will in all probability solve it.
But then again, FS2002 comes out in October and it miles superior to FS2k and the frame rates are top of the shop. I will be dumping my FS2k.