Originally Posted by
dera
You're confused here. Their GOM might require two pilots, but GOM is not an approved document.
But it is FAA accepted. The regs require compliance with a GOM as per 135.21, so if the GOM says an SIC is always required, no flights could depart without an SIC, making them required crew. Same goes for anything in a GOM, violating the GOM is violating 135.21.
Otherwise you’re right, if the GOM doesn’t explicitly state an SIC is to be designated then they’d need a 135.99 SIC PDP, or always fly IFR without A015 or PICs who complete a 135.297(g).