If you wish to assign the same crew to the next sector or series of sectors, it is possible to copy the crew by left clicking on the flight from which the crew should be copied. Then select Copy Crew or use shortcut C and select the next sector/sectors to which the crew should be copied and select Paste Crew or use shortcut V.
In order to copy crew to more than one sector it is necessary to hold Shift or Ctrl key while selecting the sectors to which the crew should be copied.
Once this is done the Assign flight crew pop-up window will appear with the entire crew already selected. At this point it is possible to deselect some of the crew members.