Originally Posted by
DenverBrian
There are only so many flight numbers to go around. If you assign outbound and inbound to the same number (DFW-MEX and MEX-DFW, for instance), you are assured that both flights can't be in the air at the same time, so it reduces potential confusion.
Or they could do what LUS did/does on many flights and have the same aircraft operate both legs, like US516 running MCO-PHX-SMF. Much less confusing than having the outbound and return flights run under the same flight number, and much less misleading than having the same flight number with a change of equipment halfway through, which in my opinion the DOT should move to stop.