Originally Posted by
mbarreto
I'm no expert, but if your upgrade doesn't clear at T-24, you'll be added to the airport upgrade list once you check in. If your upgrade doesn't clear, you'll get the $$$ and miles back!
+1
If you had looked carefully, the booking screen where you clicked "upgrade" would have said that "waitlist only" was available.
This is called a "Mileage Plus Upgrade Award." It is described here:
http://www.united.com/web/en-US/cont...grade/mua.aspx