[theYipster]

Um, Southwest participates in the IATA clearing house. You put up the wrong list. Here is the right one: https://www.iata.org/contentassets/82a24c7a736142b6bd18e20f7...

And now for some industry education. You can participate without being an IATA member. Southwest likely started when they started flying internationally in 2014. You practically can't be an airline with international flights without participating. IATA runs the global clearinghouse.

Notably, IATA does not run the clearinghouse for US domestic (and for foreign airline tickets purchased in the US.) That's ARC (Airline Reporting Corporation.) Southwest is also a member there.

[inferiorhuman]

OOf. I did intend to link to the list of IATA members, but I naively assumed that because Southwest does most things in house and does not have any interline agreements that they would also have no reason to be party to a clearinghouse. Of course now that they started pushing reservation stuff to various GDS platforms (beginning in 2020 give or take) they have a use for a common settlement method.