On 4 July 2002, VH-VBC, a Boeing 737-7Q8 aircraft, was pushed back from Bay 93 at the Domestic-4 apron at Sydney Airport before departure for a flight to Brisbane. At the completion of the pushback, one of the dispatch engineers used the aircraft ground interphone to instruct the pilot in command to park the aircraft brakes. The pilot in command responded with the phrase "Brakes parked, clear to disconnect". The towbar was disconnected, and the crew commenced to taxi the aircraft before the ground interphone had been disconnected. Consequently, the ground engineer who was operating the ground interphone came into close proximity to the right engine as the aircraft began to move forward.
The crew of VBC had operated an earlier flight from Melbourne to Sydney and arrived 21 minutes behind schedule. Consequently, VBC commenced pushback five minutes behind the scheduled departure time for the flight to Brisbane.
Runway 25 was in use at the time and a number of aircraft were using taxiway Golf located adjacent to the Domestic-4 apron. A Saab Aircraft SF-340 aircraft, VH-OLM was taxying inbound for Bay 94A on the Domestic-4 apron. An aero-medical aircraft was following OLM on taxiway Golf, and was taxying to the eastern general aviation parking area, located to the north of the threshold of runway 25.
As VBC commenced the pushback from Bay 93 to towbar disconnect point east, the crew of another B737 located on Bay 91 also requested pushback approval. The air traffic controller did not respond to that request. The controller asked the crew of OLM if they could taxi onto the Domestic-4 apron and then to Bay 94, once VBC had moved forward from towbar disconnect point east. The controller then instructed the crew of VBC to hold clear of the entrance to the Domestic-4 apron so that OLM could enter the apron to allow the aero-medical aircraft to continue taxying towards the eastern general aviation parking area.
The crew of OLM taxied into the Domestic-4 apron, and stopped in the vicinity of towbar disconnect point west, facing VBC, which was at that time located slightly to the east of, and facing west towards towbar disconnect point east.
The controller then instructed the crew of VBC to tow forward to towbar disconnect point east. The crew of VBC advised the controller that the towbar disconnect procedure was complete, and that they could taxi as required. The controller responded by issuing a clearance to the crew of VBC to taxi forward and hold short of taxiway Golf.
The dispatch engineers subsequently reported that their attention had been diverted when OLM taxied into the Domestic-4 apron and onto towbar disconnect point west. The dispatch engineer communicating with the crew recalled that the pilot in command confirmed that the aircraft brakes were parked, but could not recall hearing the pilot in command's instruction "Clear to disconnect". The other dispatch engineer, who was standing at the nose of the aircraft, subsequently reported that he realised the aircraft had begun to move forward when he felt a "bump" on the back of his head as it was contacted by the aircraft radome. He immediately turned, and realising that the other engineer had not noticed that VBC had begun to move, ran aft and dragged the other engineer clear of the vicinity of the right engine. The crew of VBC realised that the disconnect procedure had not been completed and stopped the aircraft. The disconnect procedure was completed and the aircraft recommenced taxying once the dispatch engineers had positioned themselves clear of the aircraft.
The crew of OLM taxied onto Bay 94A once VBC had recommenced taxying and was clear of towbar disconnect point east.
The operator reported that the flight interphone system from VBC was examined following the occurrence, and was found to be serviceable.
The operator's pushback procedures specified that at the completion of the pushback manoeuvre, the dispatch engineer would use the ground interphone to instruct the pilot in command to park the aircraft brakes. The correct response from the pilot in command was "Brakes parked", at which point the dispatch engineer was required to place a chock in front of the aircraft nose wheel and disconnect the pushback tow motor from the aircraft. The dispatch engineers did not place the nose wheel chock in position following the pushback.
The operator's procedures also specified that when the towbar had been disconnected and the steering bypass pin removed from the aircraft, the dispatch engineers were to stand by for the final command from the pilot in command to disconnect the ground interphone unit, using the phrase "Clear to disconnect". When given that command, the dispatch engineers were to disconnect the interphone, close the interphone panel door, and remove the nose wheel chock. They were then required to position themselves clear of the aircraft and in view of the flight crew so that the crew could confirm that the disconnect procedures were complete. The crew, however, commenced to taxi the aircraft without ensuring that the dispatch engineers were clear of the aircraft, and that the disconnect procedures were complete.