Originally Posted by
parabellum
It has always been my understanding that total command, from a legal point of view, commences when engineers and traffic staff have completed their tasks, the load sheet is signed and the doors are closed. Obviously the captain will have important decisions to make from the time he signs on until the doors close regarding the operation of the aircraft and crew but it is unlikely he will become involved in seating disputes, other than if jump seats are requested. The dispute here is entirely the responsibility of the ground staff and does not come within the captain's remit.
Yep, I take istontthatbloodyhard's comment that the reality is probably something different with ground staff not hanging around and I think you're on the money, that when the doors are closed if something happens on board I've always thought despite the GSE standby, etc. that surely it's going to be the PIC who is the person on board in authority to deal with it... thinking about this a bit more, I may have been getting confused with what I think is a CASA definition that the 'flight' commences when the aircraft starts moving under its own power but the PIC authority, somewhere between doors closed and that point.