Kenny said-
In the US, RPT or 121 carriers as they're known, can never have 1 pilot left alone in the cockpit. So if one of the drivers needs a physiological break, an FA has to come in. The only time you don't have to do this is when you have another pilot in the jumpseat.
Ok, Im going to ask for the FAR 121 para reference that says that. Never ever heard of that one and I studied 121 back in the mid nineties and flew FAR 135 up until a few yrs ago.