If I want to stand-by for a same-day earlier flight using a discounted ticket, I simply ask an agent at the airport to put me on the stand-by list for that flight. If I get on the earlier flight, my reservation on the later one is cancelled. Makes sense.

What if I want to stand-by for a same-day later flight? Should I call AC reservations ahead of time, cancel my original reservation, and ask to be put on the stand-by list for the later flight? Can AC reservations even do this? Or do I just show up at the airport for the later flight and not worry about the original reservation?

I rarely standby for a later same day flight (which is why I reserve the latest flight in the day that I might want to travel on) but when I have, I have always cancelled my existing reservation and let them know I will be standing by (always check ITN to make sure there are lots of seats before doing this).

Can't remember if I have done this at the airport or reservations or both. Reservations will cancel but I don't think they can put you on a standby list.

As a SE or E it is easier but if I was a basic member I would be retiscent to standby for a later flight.

Thanks. If I do this, I will definitely check ITN before I cancel the first reservation!

I find the gate or airport agents not really helpful to standby passenger with discount tickets. They often tell me to wait until very last minute even when the plane is half-empty. For some reasons they refused to tell me my chance of getting on and they just print me a gate-pass to go for waiting.

I don't quite understand their logic. If the plane is half-empty half an hour prior to departure. Do they expect to get them filled within a few minutes? Why can't they simply give me a boarding pass at check-in? The person who drops me at the airport has to wait for me to get an answer. If there is no seat, then I will go back to the city to wait for later... These agents really need to learn how to make the passengers and their faimly's life easier.

On the other hand, I will give them some credits on their worry. If a flight is cancelled or missed, those passengers have highest priority (even above SEs) for the next flight out. So keep this in mind when you stand by for a later flight, if the one before it is cancelled, then an empty flight becomes oversold all of a sudden. So don't stand by for the last flight of the day to go to important places if I were you.

I think there is a rule that they can only start accepting standby 20 mins before takeoff? Maybe Secret Agent can confirm this.

Basically it just comes down to how we have to check-in a standby passenger. The passenger is "go-showed" because there is no reservation to check in against. The transaction automatically qeues the passenger to the gate standby list if the flight is close to full. The gate standby list is cleared after flight close-out (20 minutes domestic, 30 minutes transborder). This is when the gate agent is able to release pre-assigned seats and reassign them to standbys.
If the flight is no where close to full, the computer will assign the standby passenger a seat at check-in unless it has been manually disabled from doing so for one reason or another. I, for one, have no problem telling a passenger what I honestly think their chances are as long as they are willing to accept that it is a guess and not a promise.