Southwest today released their flight schedule from mid-March through April 12. No, no Southwest flights from Charlotte yet but the some of the changes to changes to existing AirTran and Southwest service from Charlotte and Raleigh are interesting.

We’ve previously discussed Southwest and AirTran service to the Carolinas, and what we can infer from that that about possible Southwest service from Charlotte. So time for a bit of an update:

Charlotte on AirTran: AirTran goes to only 3 daily Atlanta, 2 daily Baltimore in January and continues at that level through through into April. This is comparable to 2011, aside from Orlando service ending. Be interesting to see whether they add a third Baltimore flight next summer, like they had this summer (and on through to early January)

Raleigh/Durham (RDU): To no great surprise, Southwest is ending service from RDU to Philadelphia (PHL) come mid-March. We’ve already said Southwest wasn’t going to fly from Charlotte to Philly and this just comes as further proof. The Philadelphia focus city experiment was a failure for Southwest, and the city now just another spoke for the airline, much like RDU.

Speaking of RDU, Southwest and AirTran are combining for 29 flights a day in late March and early April: 3 x Atlanta, 6 x Baltimore, 3 x Chicago Midway, 1 x Denver, 1 x Ft. Lauderdale, 1 x Las Vegas, 2 x Houston, 4 x Nashville, 3 x Orlando, 1 x Phoenix, 1 x St. Louis, s x Tampa, for 29 total, or seven flights off this summer’s peak. Philly was three flights of that, while Atlanta, Baltimore, Midway, Denver, and Orlando are down a flight each, though those frequencies could very well return for the peak season. Oh, and Houston is up a flight versus last summer.

Said previously that for Southwest service from Charlotte:

The wildcards are Houston and Nashville. Nashville is about 90 percent of the market size (by dollar value) of Atlanta but only one airline current serves the route (US Airways, of course). So that seems possible. Houston once a day? Maybe, Southwest does that sort of stuff.

That Houston is now twice a day from RDU makes a CLT-Houston more likely in the future.