Or to put it another (simpler) way:
B737-400 - Air Atlanta
B737-800 - Excel
B747-300 - Air Atlanta
B757-200 - Air Atlanta (being transferred over to UK reg)
B767-200 - Air Atlanta (ditto)
B767-300 - Air Atlanta (ditto)
MD83 - Skywings
The 800s pretty much look after themselves, but the merger with Air Atlanta has caused all sorts of issues with the leased aircraft so until the paperwork is complete, nothing can really be done with regards replacing the fleet. 900s on their way to replace 757s is just about it. Any rumour of a 747-400 joining the fleet soon?? May have got my wires crossed with that one.
Cost effectivity is clear when you have a look at the state of the leased aircraft! The airline can't be paying big bucks for them.
MD-83 just there for the summer to take advantage of the market at EMA and someone who counts beans worked out it will be profitable so that's why it's there. Again, a pretty minging aircraft but it gets people from A to B in one piece and back again so job done! Ditto with the 734 at NCL. And the jumbos...