Originally Posted by
ORDnHKG
Why ?
I assume you meant AA flight number operated by Republic and not earn MP miles, not US.
You do know that there are UA express operated by Republic too right ? It is the exact same thing.
This is not new at all, no matter *A, oneworld, or skyteam, there are so many flights that are codeshare and operated by another carrier, it is always the metal determines what you earn.
I think what OP meant was you could fly on a Republic operated flight, marketed as AA but possibly sold by US and carrying a US flight number since most AA flights are now also US codeshares. Thus you are on a "US" flight operated by Republic for AA and thus no miles. Or you could buy a US Airways Express flight operated by Republic and earn MP miles; thus it's not quite the "exact same thing" for mileage earning purposes.
I can see how it would be confusing, but if you buy a US ticket on the US Airways website they do indicate the flights that are "operated by AA" or an AA affiliate. Don't book those if you want MP miles.