Originally Posted by
j2simpso
Disclaimer : I haven't tried this before but have had some experience with SDCs.
My understanding of how it works is when you get a upgrade with miles/certificate award your fare code changes to R$ where $ represents the original fare basis (i.e. RK if you originally were booked on a K fare). Hence for the purpose of rebooking, and SDCs, UA will look for inventory based on your original fare basis (i.e. K fare) which I suspect will give you options since there's generally more Y than F availability. Once you complete the SDC you'll be back in your original fare class (i.e. K) unless there is upgrade availability at the time of SDC or between SDC and your plane leaving the gate. If the upgrade never clears you should then be given your miles back.
Safe Travels,
James
If I upgrade with cash, my experience has been P, if I upgrade to with Miles, its R. A quick search for this weeks flights shows P often exceeds R. Not that $139 is a big deal for me for the upgrade, but 15,000 miles for the upgrade with all the miles I have is my preferred option. Fare class as of now is H if it matters. So regardless of how I upgrade, I would need H plus R or P, depending on how I upgraded?