The way it normally works (I'm going by SHARES/Apollo/SABRE based carriers only because I've seen it in action
) has a lot to do with the software being used by the carrier.
The seat map is compared one to one by the system. Automatic reaccommodation is done dependant on original seat assignment. If you had an aisle, it will attempt to give you an aisle. If you had a window, it will attempt to give you a window. If you have four people sitting next to each other all in the same booking, it will attempt to keep the party together.
In the event it runs out of "options" it will then go in order of frequent flyer status/fare paid (or both, dependant on the system) until it assigns all the seats it can. Anything over and above gets rejected for manual processing.
If the change of aircraft happens at the gate....
|Quoting Bri2k1 (Reply 5):|
In my experience, they usually change planes at the last possible second. This results in a massive line forming behind the gate counter, a couple hundred upset passengers, and 3 or 4 very unhappy CSRs.
is exactly what happens.