Only transport sized planes I've seen that board in the back are the ATRs. They have a baggage compartment between the cabin and the cockpit.
They boarded in the back on AA from MIA to STT this year. Twin jets, either 737s or Airbus 300 series. Maybe even deplaned there too? Maybe even Delta on a second trip? I don’t recall that one. No AA ATRs in years.
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