95b323b7_of_Size__Policies___Yahoo_News__Stated_policy
[Airline] JetBlue [Costs] Passengers do have the option to purchase a second seat, regardless of size, at the current fare offered. No refunds are offered. [Stated policy] 
The airline does not officially require the purchase of a second seat; armrests are 17.8 apart, good news for many larger customers.
Airline "Customer of Size" Policies - Yahoo News
Stated policy