Originally Posted by
volta
This is one of the beautiful things when flying in the US. Most US domestic flights are two cabin flights, with F and Y. The F is pretty bad (or insert your favorite adjective here), but it is considered F class fare, so F class mileage redemptions are charged.
Luckily -- to give a shout-out to UA .... their award structure differentiates between F on a 2-class and 3-class aircraft.