Originally Posted by
n8-the-gr8
What drives the fare basis?....
The fare rules for that fare basis and UA will, by default, use the cheapest fare / fare basis that you meet the fare rules
Things that may eliminate cheaper fare / fare basis are
- Fare class inventory
- Day of the week
- Advance purchase requirements
- min / max stay
- routing
- ...
Same sort of things covered in
Fare Class has Inventory - Not Able to Book into?
There may be multiple fare/ basis for a given fare class but with different fare rules -- particularly advance purchase timeframes