Use of upgrafe certificates
 

I had an unvoluntary downgrade (from F to C)and was given an Uprgarde certificate this is a "one-class, one-sector complimentary upgrade based on seat availability at the time of check-in". This is a bit cheap from CX, as I had no choice when downgraded and paid for F. But that's not the point. My question is a practical one: what do they mean by time of check-in? Can I do it at OLCI, and how? If only at airport, should I arrive very early and when will they decide that there is an empty seat (actually two as my wife has the same) and honor my certificate? I might do it from CDG, NRT or HKG, anyone has experience? I thank you very much for your practical help.

I hope that your downgrade from F to C had been compensated with more than just the voucher! It is most often a combination of cash plus voucher. The upgrade part of the voucher is only confirmable at time of airport check-in. Don't waste it on short haul routes like NRT or TPE, since you can only use it once.

Thats exactly what it says. You cannot book your upgrade in advance, and cannot do OLCI to secure your seat. It can only be done at the airport at time of check-in. You may go to airport earlier to make sure that you get your seat but it would be great to check what are the loads in F that day too. If there is only 1 seat left, obviously both of you can't travel at the same time!