Originally Posted by QRC3288

I'm a little confused what you're trying to do. (AA OWE is irrelevant, regardless.) So I'll just dump information.

You can pay the milage difference. Given you're on an around-the-world flight this might be a complicated calculation. But in theory, you can pay the mileage difference, always.

There is occasionally a "bidding" option, but that's done online well in advance, and is often a stupid price, basically the fare difference if anecdotes on here are reliable. There isn't America-style "let's make a deal" at the airport, if that's part of your question. They will just let the cabin go out with seats empty.

Redemptions 1: you cannot break your itinerary up. So you can't "cancel" one segment and replace it with an outright redemption booking. (Therefore AA miles are useless here).

Redemptions 2: Cathay does offer a one-class redemption upgrade, but only certain sub fareclasses are eligible I believe. I *think* it's YBHKLV? But not 100% sure. If you're on an eligible fare class, and if redemption space opens up, I think you can use Asia Miles to upgrade your sector without impacting your underlying ticket.

What the paragraph above means is, you'll need to have Asia Miles in your Cathay / Asia Miles account asap, if you want there to be a chance. But you should also check on the rest because it's possible it's just hopeless to begin with.