95b323b7_of_Size__Policies___Yahoo_News__Stated_policy
[Airline] Airtran [Costs] The airline will sell you the seat at the lowest available cost. Yes. Passengers on below-capacity flights can request a refund for the cost of the second seat. [Stated policy] 
If a customer cannot lower the armrest, they will be required to purchase an extra seat. If none are available, they may not be able to fly.
Airline "Customer of Size" Policies - Yahoo News
Stated policy