Is it possible to certify an aircraft under FAR 23 Commuter Category with single pilot ops only? Like, there is just one seat in the cockpit and up to 19 passengers. Does anyone know of such an aircraft flying?
It looks like it's possible but not common. There's an STC for the Twin Otter that authorizes single-pilot operations in the commuter category if various upgrades have been made. At least, that's my reading of it:
The Twin Otter DHC-6-300HG™ type rating designation is DHC-6HG and may be operated with or without a second in command (SIC) with certain limitations. The Airplane Flight Manual Supplement (AFMS) lists equipment that must be installed and operative to operate the aircraft single pilot.
FAA STC SA02682LA incorporates upgraded engines, upgraded propellers, increased maximum takeoff weights (MTOW), structural and aerodynamic modifications, and the aircraft category and design characteristics were updated to Title 14 of the Code of Federal Regulations (14 CFR) part 23 commuter category.
HondaJet is certified for single-pilot operation for Part 23. Note that 14 CFR Part 23 Amendment 64 and later removed Utility, Acrobatic, and Commuter Categories and now refer to all of them as Normal Category.
CE-501SP and the CE-551SP are FAR part 23 certified aircraft. Both of these airplanes may be flown single pilot without a waiver as long as your checkride was completed in one of these aircraft to single pilot standards.