You can now use your Southwest companion pass on certain AirTran routes. If you can purchase the ticket on Southwest.com for an AirTran code-share flight, then it works. This has not been publicized, but it works. For example, Atlanta-Ft. Lauderdale now works when purchased on Southwest.com and booked on AirTran for companion passes. In addition, when you book on Southwest.com you get the two bags free allowance.