During Take Off & GA Auto Thrust is not engaged.
During a GA, either auto thrust should be designed to disengage automatically or pilot's trained to disengage it.
Depends on type i would think. On the boeing (737) you have auto thrust engaged for take off and GA (the latter depending on SOP). Of course during take off roll the mode will change to THR HLD and later on to ARM until climb thrust which engages automatically at a preset height.
Dunno about the bus though, they might do it differently.