Originally Posted by
flyerCO
Cant have same flight number. One would cause confusion for passengers. Two, ATC systems cant handle this. Ie with a direct flight, if the 2nd portion takes off while 1st half is delayed, still in air, airline must uset"fake" flight number for ATC. Ie 9989
For situations like this, I have also seen Flightaware/FR24 (and presumably ATC systems) append a character to the original flight number (if <=3 digits).