three souls on board are likely the captain, copilot, and flight engineer…
Well yeah, someone's gotta fly the plane.
https://aviation.stackexchange.com/questions/12452/what-is-the-typical-aircrew-for-a-cargo-flight
It's not atypical.. "flight engineer" or loadmaster would generally fly along with the pilot/copilot for atlas… almost got hired on in such a position a long time ago.