If you do not have any textures at any airports at all about the only way I know to fix that is to uninstall and reinstall FS.
If this is at just one airport have you added any new scenery to that area if so try turning it off and see what happens then. If you have not added any thing new you might be able to reload that scenery from one of the orignal disks. Other wise you will still have to uninstall and reinstall FS. Sorry I do not rember which disk the scenery is on but you should find it in one of the CAB. files just unzip them to any folder other than FS
DO NOT UNDER ANY CIRCUMSTANCE UNZIP ANY CAB FILE TO YOU FS FOLDER
Once you have the file unzipped you can just drag the scenery over to fs and click overwrite. 8)