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.
To my knowledge and experience, the rule is that M&M awards on two class aircraft within mainland US (no matter which StarAlliance airline) are charged at Y and C mileage, even if the cabins are called "Y" and "F" by the operating airline. However, on two class aircraft between mainland US and Hawaii, awards are generally charged at Y and F mileage, except if the operating airline calls the front cabin "business" (in which case C-award levels apply).
Used to be different many years ago (when also Hawaii was consistently charged at Y/C).