Aviation safety investigations & reports

Boeing Co 737-7Q8, VH-VBC

Investigation number:
200203102
Status: Completed
Investigation completed

Summary

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.

Analysis

Although the pushback of VBC was five minutes behind schedule, there was no evidence to suggest that the pushback was rushed in the interests of any commercial pressures on any of the personnel involved.

Following the instruction to "Park brakes", the pilot in command responded, "Brakes parked, clear to disconnect", without a pause between the two instructions. The dispatch engineer communicating with the crew recalled that the pilot in command had confirmed that the aircraft brakes were parked, but could not recall hearing the pilot in command's instruction "Clear to disconnect". At about that time, the attention of both dispatch engineer's was diverted by OLM taxying onto towbar disconnect point west. It is possible that the dispatch engineer in communication with the crew may not have heard the "Clear to disconnect" instruction from the pilot in command because of the noise of the engines of both VBC and OLM, and also because his attention had been diverted by OLM.

The nose wheel of the aircraft was not chocked at the completion of the pushback. That was contrary to the operator's prescribed procedures. Had the nose wheel been chocked, it is unlikely that the aircraft could have moved forward until the disconnect procedure was completed.

It is likely that once the crew of VBC saw the pushback tow motor clearing the aircraft, they incorrectly assumed that the disconnect procedure was complete, in accordance with the pilot in command's instruction of "Clear to disconnect" to the dispatch engineer. At that point, the controller requested the crew to tow forward. The crew's response to the controller that the disconnect procedure was complete, and that they could taxi as required, seemed to support that assumption. However, the crew commenced to taxi without ensuring that the dispatch engineers were positioned clear of the aircraft, thus providing confirmation that the disconnect procedure was complete.

Significant Factors

  1. The aircraft nose wheel was not chocked following the pushback manoeuvre.
  2. The crew commenced to taxi without ensuring that the disconnect procedures had been completed, and that the dispatch engineers were clear of the aircraft.



Safety Action

Aircraft operator local safety action

The operator has amended its pushback procedures in the event that the pilot in command advises "brakes parked", "clear to disconnect" without a pause between the two instructions. After the Captain confirms that the brakes are parked, a chock is to be placed in front of the nose wheel while the tow bar is being disconnected. The tow bar is to be disconnected from the aircraft and the steering bypass pin removed. The dispatch engineers are to then disconnect the interphone, close the interphone panel door and remove the nose wheel chock, then position clear of the aircraft and in view of the crew.

The amended procedure reinterates the previous requirement for two chocks to be carried on the tow motor for all aircraft movements.

Airport operator local safety action

The airport operator has revised the operational procedures for the Domestic-4 apron. The revised procedures specify that aircraft movements to/from Bays 93, 93A, 93R, 94, 94A and 94B are not permitted when towbar disconnect point east is occupied.

General details
Date: 04 July 2002   Investigation status: Completed  
Time: 1615 hours EST    
Location   (show map): Sydney, Aero.    
State: New South Wales   Occurrence type: Ground handling  
Release date: 13 March 2003   Occurrence category: Incident  
Report status: Final   Highest injury level: None  

Aircraft details

Aircraft details
Aircraft manufacturer The Boeing Company  
Aircraft model 737  
Aircraft registration VH-VBC  
Serial number 30638  
Type of operation Air Transport High Capacity  
Damage to aircraft Nil  
Departure point Sydney, NSW  
Departure time 1615 hours EST  
Destination Brisbane, QLD  
Last update 13 May 2014