Sorry Dark, this is one time you are wrong. Air Slash is not that good because Swellow has higher Attack. Here is my recommended moveset:
Brave Bird: High power, high accuracy, STAB, Roost heals Swellow. Make sure to also hold a Shell Bell for quick healing right away.
Roost: Used to heal Swellow, especially from Brave Bird recoil.
Steel Wing: Decent power, decent accuracy, chance to raise defense, used to deal with Rock and Ice types.
Facade: If you do ever get a status condition, this combined with Guts will become incredibly powerful. If you get poisoned or burned, the Shell Bell will heal you also. If you don't have a status condition then this move still has decent power, high accuracy, and STAB.