I noticed that Southwest has a lot of advance purchase PHL-ATL fares for September-December at $109 WGA. That's a lot more competitive than what it was charging for awhile especially around the time ILG-ATL was announced. ATL is about the same distance as MDW but PHL-MDW is no less than $149 WGA.

I'm just watching this route as Southwest inherited it, and Southwest has to compete against Delta and US who have FF from each side from their local markets, and Frontier has come in likely picking off leisure pax but using TTN and ILG.

Southwest service decreases down to 3x daily so I think Southwest is now trying to get more O&D for this route by lowering the fares, not just fill up by connections.

I do wonder Frontier's effect on TTN-ATL and ILG-ATL is having a siphoning effect and prompting Southwest to determine viability of it's own PHL-ATL on it's metal.