UuA based on fare basis or booking class?
I'm working on a tentative booking in WT+ LAX-LHR-JNB-LHR-LAX. The fare basis is TLNCNAS, however T class isn't available on one of the segments so it is booked in Y. My question is when I try to upgrade, will the segment that is booked in Y (on a T-fare) be upgradable to WT+ or CW?