It's not quite that simple. Rule Part 1 states "4 or more".
So that really means if you are operating more than 3 then its a regular air transport (passenger) service.
So you can fly A-B, in, out, and in. Your next out is 4!
Confirmed by Airline Group Ops Inspector.
Personally I think the intent of the definition was meant to mean more than 4, but there you go......
By the way I'm an ex 119, 135, 125, 121 QA Manager. I doubt though, that adds any credibility to my interpretation of the rules.
