Originally Posted by
Mongah
Both. It could be Mongah Airlines flight 999 from Fresno to Sydney with a stop in LAX. Same flight number but the flight from Fresno is a CRJ and the outbound from LAX is a 747. CRJ in flight is Flt999 while the towed 747 is 999A.
You can also have two airborne flights of 999. If the CRJ from Fresno is late with the 3 connecting passengers but the other 250 people made the outbound from LAX and it left, the outbound from LAX would depart as 999A or the CRJ may be assigned 999A if it was delayed and left Fresno after the LAX outbound departure time.
I thought in this sort of situation they give the second flight to take off a very different flight number (like 9099 instead of 99) to avoid any potential confusion if they are in the same ATC zone.