Single/double pilot planes
What are the biggest planes that are deliberately flown by one pilot?
All airliners can, in emergency, be landed by one pilot and it is acceptable for one pilot to leave the cockpit sometimes in cruise, like for lavatory visits. But they are not supposed to be deliberately flown with one pilot. And neither are big business jets.
Cessna, however, has a fair number of jets which can be flown by single pilot. Those are planes with two pilot seats in cockpit. Some of those Cessnas can be deliberately flown with one pilot seats empty. Other Cessnas, often versions of the same models, are not to be deliberately flown solo.
What is the difference in cockpit between Cessnas which can deliberately be flown solo and those which may not deliberately flown solo?
Also, I hear that a plenty of manufacturers are coming out of woodwork to manufacture Very Light Jets, with two pilot seats but supposed to be flown alone. Many of those manufacturers are previously unheard of. Some are not. For example, Embraer Phenom 100 is supposed to be flown solo. Embraer also manufactures other planes - including airlines.
What exactly makes those pressurized, high-speed, high altitude twin turbofans so easy to fly that it can be done alone?