Originally Posted by
ijgordon
What class of service are you allowed to upgrade to/from?
For *A the rules are that you must buy a Y or B fare to upgrade to biz. They cannot be booked on codeshares, either. The upgrades are per-segment (MCO-ORD-IST would require one upgrade for MCO-ORD and another for ORD-IST) and are painfully expensive on top of having to buy the incredibly expensive fare. It is, quite frankly, a bad plan.
AFAIK neither US, UA nor AC fly their own metal to IST so that's not going to help you much.
If you do it with LH, LX or OS you'll get intra-Europe C on the onward connection and that is just glorified Y with a blocked middle seat and slightly upgraded food. Likely not worth spending the miles on that segment.
Given that you need the same award inventory as a straight C redemption for the Y->C upgrade I'd just focus on finding the award seat and redeem it. You can mix and match carriers more easily and likely spend less total money/miles.