Its becoming plainly obvious that Airtran needs to supplement is large and growing fleet of 717s with a longer, larger craft. Why?
1) To add flights to western destinations such as LAS, DEN, and SLC
2) To add flights to the Carribean such as SJU, MBJ
3) To increase lift on high demand flights like ATL-LGA, ATL-MCO, ATl-MIA, and ATL-FLL
In my opinion the best choice for new aircraft would be the MD-90. It has superior range to the 717, larger capacity, and while relatively cheap, is becoming widely available.
1) AA is returning to Boeing 5 exQQ (Reno Air) MD-90s that do not fit with its Super80 fleet. Perhaps FL could pick up some of those at favorale rates.
2) Air Aruba recently ceased all operations. Air Aruba had 3 (I think) MD-90s. Where will they go? Perhaps FL could get some of those at fire-sale prices.
3) FL's neighbor DL is a large MD-90 operator, but is gradually decreasing their usage. Perhaps FL could get some of those as DL replaces its 90s with 737s.