Originally Posted by ashill

...

If they weren't interline partners, you couldn't buy such a ticket. For reference, most of the major airlines are interline partners with most other airlines (with the notable exception of Southwest, which has few if any interline partners). It's the lowest level of partnership.

Interline Agreements:
Flying WN
E-Ticket Interline Agreements
    Paper Ticket and Baggage Interline Agreements

   MAY ISSUE TICKETS INCLUDING
       WN                                                      
 
   MAY CHECK BAGGAGE TO
       WN