Originally Posted by
mgeldere
An alternative is Chinese travel agent Ctrip - they actually have the option to, on quite a few flights - not all - select from multiple booking classes. During the booking process you can choose the actual booking class. It won't show the 'letter' of the booking class but it will warn you if it is a non-mileage accruing booking class.
The letters (far codes) correspond directly with percent discounts from Y (e.g. 9折=B); MU maintains a chart of these somewhere on its China site.