J-F
As the term involintary is meant to mean, they up-grade you at their cost.
Cant wait for the check in staff at HKIA to apply this....yeah right...
By the way, our tickets have always been upgradable, involuntarily...however, you were more likely to end up in Y rather than F as was the intention. Some people even carried around the section from Vol 1 that showed this, never really helped them much though!!!