I can only get the 50% airport trade bonus with cities of another civ, which kind of sucks!
Last night me and arii finished off a space race game.  I created 3 caravans in cheat mode and sent them to his cap, i also created a airports in both cities.  Trade routes then went from 28 (trade with our own cities) to +50/routes.  Is it possible to do this with trade to your own cities?
  
  
<font size=1 face=Arial color=444444>[This message has been edited by markusf (edited January 14, 2001).]</font>