One VH registered airline operating 737 Classics and operating to Nauru on a scheduled service uses Cruise captains. These are first officers who are authorised by CASA to log in command time when the captain is on rest but are not permitted to log command time for take off and landings or below a certain altitude. There is nothing in the Australian Regulations that permit this and one wonders if this practice is authorised by a local FOI with the knowledge of CASA Head Office? Certainly a very useful way of building command hours on a large jet - but what is the CASA Regulation that permits this practice? And if there isn't one then surely this is illegal. According to the Regulations there can only be one captain for the whole flight from take off to landing even if he is absent from the flight deck for an indeterminate time.