I'm looking to book RT tix from BKK to USM, and would prefer to book the "Blue Ribbon" class - when I try to book on the Amex travel website, it's only showing economy, but in a range of fares Q/M and D. The price in D is the same as the "Blue Ribbon" price on the Bangkok Airways site (I want to use up an Amex credit) Is there some reason the flight is showing as code "D" it it is in the business section?

Thanks