I recently purchased some economy tickets for USA west coast to IST (and beyond). I intentially paid ~$500 more than the cheapest economy, so get into a fare basis that I was told was upgradeable. Hoping to use my United miles for the upgrade... but so far, it doesnt appear that TK has "released" seats to be upgraded to. Any idea how far in advance TK does this? Do they release ALL physical open seats, to available for upgrade at some point (24 hours? 48 hours?) before flight time? What about a cash upgrade, at that point, or at airport? Does TK do that? If so, what is the typical upgrade cost?