The Metro conundrum
From my memory, but be gentle, I am getting old, the Metroliner 111 was certified as both Single pilot or 2 Crew in Australia. It weighed in at around 7200kg MTOW, so well above 5700kg which would normally require an ATPL. I seem to remember it was a "Grandfather" rule from the Merlin/Metro 11.
The weird thing was, you could fly it Single pilot without an ATPL, but if you flew it 2 Crew, you needed an ATPL.
I can't remember why the differing ATPL requirement, something about the Multi-crew thing? Maybe someone from the Jetcraft/Pelair freight world can fill in the blanks.
I think the B1900 and the KingAir 350 have the same requirements.