Originally Posted by
Phoenician Aviator
That still makes no sense, UnitedSkies. I understand the distinction that "Heavy" implies, but I don't understand the logic behind the alpha characters in the callsign. Why add "Juliet" at all? Either way, you're still saying that the SFO-ORD flight is "X" and the ORD-GRU flight is "X + A".
The Juliet is just like the 8XXX. It is used to differentiate two flights that would otherwise have the same call sign in the ATC system.