Much as I wouldn't want to preempt Randy, I use a Greaemonkey script for Firefox that does just what you ask for. You can get it from: http://www.doc.ic.ac.uk/~abuckley/airports.html. It generally works really well, although I've found it mangles some URLs in posts where the URL contains an airport code (if this happens, you can just disable the script temporarily from the Greasemonkey menu).

If you're not using Firefox, then I suggest you start doing so