Originally Posted by
MSPeconomist
You can't upgrade with DL miles on VS. Also, AF tends not to make upgrade inventory available, but M B Y fares upgrade into premium economy while some premium economy fares can upgrade into business class.
Thats a pretty sucky propostion considering that M/B/Y-fares are ~$1000 more than W-fares for a poorer seat option. Not being able to upgrade to J-class directly from a high fare Y-class is ridiculous considering the pricing and the fact that higher fare W-class are impossible to book through Delta.