Just remove the select, and use:
<input type = 'hidden' name='code' value='airline code' />
Replace 'airline code' with your airline code you want to be the default
Are you on a free host?
Follow directions in my signature for getting debug info, and attache the core/logs/log.txt file after you try to add an airport
Follow the link in my signature for getting debug info,t hen you can PM me a copy of hte /core/logs/log.txt fil, and paste the output here of the install/checkdb.php and install/checkinstall.php files