Coincidental this topic has recent posts as was searching Google after experiencing a prop starting and running during boarding today. Wondered about procedures which allow this (if any) as have never come across it. As soon as last pax through the door it was closed, left prop started immediately and pushback seconds later with pax still getting seated. Safety announcement done at great speed by one of pilots, initially bilingual then single language, with single cabin crew demonstrating. Whereas on outbound the single cabin crew did it all. Clearly in a hurry to get away, as no proper cabin check was undertaken.
Not a particularly well known airport but one in the western world which receives circa 5 daily pax flights 2 of which are 737s and minimum circa 50 seats as mine was. It has a conventional terminal etc, not a gravel strip in Alaska. Being careful not to ‘name and shame’, just interested in rules and how common this is.