What happened
During a period of non-standard air traffic control operations, an aircraft with registration YFW, a type not specified, entered Amberley airspace without a formal hand-off from the Brisbane departures controller. The controller had originally intended to direct YFW to turn north to avoid the Amberley airspace boundary. However, because the aircraft did not follow the intended northern turn, it crossed into the Amberle airspace while still operating on a different radio frequency than the Amberley approach controller.
At the time, the Amberley approach controller was managing other traffic and was not expecting YFW to enter their sector. This lack of coordination, combined with the aircraft being on an unmonitored frequency, prevented the controller from effectively managing the separation of the aircraft. The situation was further complicated by a lack of communication regarding changes in the Brisbane Terminal Control Unit (TCU) configuration, which led to the Amberley approach controller contacting the incorrect Brisbane controller. This communication error resulted in a 17-second delay, which reduced the lateral separation between YFW and another aircraft by approximately 6 km.