A Jetstar Airbus A320-200, registration VH-VFV performing flight JQ-127 from Adelaide, SA (Australia) to Denpasar Bali (Indonesia), was enroute at FL340 about 540nm northnorthwest of Adelaide,SA over central Australia when the crew decided to turn back to Adelaide due to the failure of one of the hydraulic systems. The aircraft descended to FL250 for the flight back and landed safely back in Adela...