Hi EzzeBKK, this is a tricky one, it is either not allowed or the practice is not encouraged, so you cannot rely on it. The gold upgrade is handled by the reservation section whilst the upgrade is an airport matter and this is where you come unstuck because the ticket still reads as economy. The times I have been successful, the F cabin has been half empty. Nowadays you can buy 2 upgrades from certain ports ie going from Y-C-F, my thoughts are, it worth the effort. I had a 50% success rate, but it was the times I really wanted it, that they refused, so I worked around the system, buying combo fares which have one sector in business and another in economy, when I apply the gold upgrade, I am where I want to be. Hope it works out for you , regards.