|Quoting WestWing (Reply 3):|
This is quite common for all UA flights that are listed on the timetable as a domestic leg with "equipment change" and then an international leg.
So for ATC purposes, the flight that operates the domestic segment is often planned as UA 8xxx. Someone on this board reported once that their international leg had an 8xxx number, though this has never happened for me -- it has always been the domestic leg.
And yes, the reason is to avoid having two different aircraft with the same ATC callsign.
|Quoting RDUDDJI (Reply 4):|
All of this is true, plus the fact that one or two carriers somewhere over the U.S. might have the same flight number, so to make sure there's no confusion, they'll often assign another number for ATC.
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