When Vietnam Airlines joined SkyTeam a couple years ago they kept their award inventory as part of their revenue buckets. That was awesome for award travel as the inventory was quite readily available and, depending on the program, you could even get credit for flights taken on award travel. As of April 1, 2013, however, that's changing. Currently business class awards book into J class and economy awards into U class. The new booking classes will be O for business class and X for economy. With the inventory now separate from revenue bookings Vietnam Airlines can more tightly control access to the seats. And, from what I can see in a few test scans of their inventory, they are tightening down pretty badly. I’m having trouble finding any seats from Ho Chi Minh City to Singapore over the next several months, for example. And even where the inventory is still available it is more often than not in economy class, not business class, where the seats are showing. On the plus side, the new buckets are still published into the GDSen so they are publicly visible (and searchable). It is just that there isn't much out there. Some more details here: http://blog.wandr.me/2013/02/changes-coming-to-vietnam-airlines-award-booking-codes/.