A Dash 8 had departed Sydney for Port Macquarie NSW. The crew was maintaining the aircraft at flight level 170 and reported that they were ready for descent. The sector 15 C controller issued instructions for the aircraft to leave controlled airspace on descent and for the crew to contact flight service for the portion of the flight to be conducted outside controlled airspace.
The boundary of controlled airspace was 12,500 ft and the crew contacted FIS 5 prior to that level. The flight service officer received the transmission but had not had any coordination on the flight from sector 15 C. Fortunately, there were no immediate traffic conflictions, and the flight service officer had time to peruse his flight strips and pass relevant traffic information to the crew of the Dash 8.
The sector 15 C controller, who was under training, had not passed the flight details regarding the Dash 8 to FIS 5. However, a tick had been placed on the flight progress strip indicating that the coordination had been completed.
While the Dash 8 had been en-route, the military airspace under the control of Williamtown air traffic control became active and this action required coordination between sector 15 C and Williamtown control, which included information on the Dash 8. This activity resulted in a short-term, high workload situation involving several conversations with Williamtown air traffic control.
At approximately the same time, a second training officer prepared to take over the training responsibilities from the original training officer. This handover/takeover took place at the console with both officers "plugged in" to the monitor jacks. This had the effect of the second training officer being unable to hear anything through his headset until the first officer removed his headset from the jack.
The crew of the Dash 8 received their instruction to contact flight service immediately after the first training officer unplugged from the console and he did not hear this transmission. The second training officer looked at the flight progress strip as the instruction was being given and, seeing that the strip notation indicated that the coordination had been completed, believed all appropriate action had been taken.
Neither the first training officer nor the trainee could remember when or why the notation was made on the flight progress strip indicating the completion of the coordination with FIS 5 but, on reflection after the occurrence, the training officer remembered that it had not been done.
There was no breakdown in separation.