AA19 3/7 and 3/14 showing different aircraft types
I am booking AA19 on 3/7 and 3/14 to travel DFW-MIA. When searching, the flight shows it is a 777, but the seat map is of a PMUS A321. Once putting the flight on hold, the aircraft type shows as a 32B, which should be a PMAA A321.
What aircraft type should I expect on this flight?