Boeing Co 737-7Q8, VH-VBC

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.

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

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.

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.