A Boeing 737-476 aircraft was in the final stages of preparation
for an 0810 EST scheduled departure from Melbourne. It was the
aircraft's first flight of the day. The ground engineer had
completed the pre-flight and other assigned pre-departure tasks.
There was little else for him to do prior to his duties for the
pushback which included assisting the ramp towmotor driver to
connect the towbar to the towmotor and walk out with the aircraft.
The flight crew had started the Auxiliary Power Unit (APU) and were
completing the Before-Start Checklist in preparation for
pushback.
The towbar was delivered by ramp personnel at 0803 and was
connected to the aircraft nose landing gear by the engineer. At
0805, cargo loading was still in progress in both the forward and
rear cargo bays. The engineer was aware that the towmotor should
only be driven by the rostered ramp towmotor driver who was still
involved with the loading of the aircraft. Concerned that the
departure of the aircraft was about to fall behind schedule, he
decided to connect the towmotor to the towbar himself.
The engineer moved the towmotor close to the towbar, but stopped
when he noticed that the towbar was at the wrong height for
connection. He then left the cab, with the towmotor's engine
running, to correct the towbar height. While re-adjusting the
towbar, he heard the towmotor engine shut down. He reported that he
then climbed back into the towmotor, restarted the engine, and
attempted to drive forward the remaining 10 cm required for
connection.
At that time the towmotor appeared to him to move forward
"...relentlessly..." and collided with the aircraft. He indicated
that he had applied the brakes and selected reverse gear, without
success. He then vacated the cabin of the towmotor across the
deroofed front of the vehicle.
The flight crew indicated that they heard and felt a "...big
thump..." which continued and shook the aircraft for about 4-5
seconds. The pilot in command advised the cabin crew to
"...brace..." and noticed the towmotor wedged under the aircraft
nose. He assessed that there was no danger to the aircraft and
ordered that the passengers be disembarked normally through the
forward door via the aerobridge, which was still in place. He shut
down the flight deck systems, set the park brake, but left the APU
running to power the hydraulics and disembarked to view the extent
of the damage.
The aircraft had sustained substantial damage to the radome,
forward pressure bulkhead, forward fuselage skin and nose landing
gear doors.
The engineer had been employed by the operator for more than 26
years and was highly regarded as a Licensed Aircraft Maintenance
Engineer (LAME) and company employee. Supervisors indicated that
the engineer was very cooperative and willing to assist ramp staff
at all times to despatch aircraft on schedule.
At the time of the accident, the engineer was on the first day
of a shift rotation, having been off-duty for the preceding three
weeks.
The engineer held a current ramp driver's licence and had
considerable recent experience towing aircraft using another
towmotor type. He had last driven the accident towmotor about 6
months previously.
Towmotor and towbar information
The towmotor was designed specifically for B737 use. It had last
undergone maintenance action on 5 March 2001. According to the
operator's maintenance staff, the accident towmotor was used only
on the ramp as it was unsuited for maintenance purposes. It was the
only one of its type used by the operator.
The design of the towmotor was such that the towbar and
connection point at the front of the vehicle could not be seen from
the driver's seated position. Towbar connection was a two-person
operation. Any attempt by a single person to connect the vehicle
and the towbar, involved the driver having to stand up and lean
over the steering wheel to view the operation. From a standing
position, it was possible for the driver to place a foot over both
the accelerator pedal and the brake pedal simultaneously.
The cabin forward structure had been torn upwards and rearwards
during the initial contact with the aircraft. The rear left corner
of the cabin structure was forced down through the vehicle's upper
body panel by the weight of the aircraft's nose. Inspection of the
towmotor found no mechanical fault that could have contributed to
the accident.
The towbar for the Boeing 737 aircraft underwent a complete
service on 28 March 2001 and had been correctly connected to the
nose landing gear strut of the aircraft. Impact from the towmotor
sheared the towbar's rear shear pin, which allowed the bar to
swivel out of the way, pivoting on the remaining shear pin, as the
towmotor drove forward into contact with the aircraft. The towbar
was inspected and found to have been serviceable at the time of the
accident.
Aircraft pushback procedures
Aircraft pushback procedures at the time of the accident were
contained in the operator's Ramp Standard Operating Procedures
(SOP). The SOP stated that the towbar was to be delivered to the
aircraft by ramp personnel, then connected to the nose landing gear
by the engineer. Connection to the towmotor was to be accomplished
by the rostered ramp towmotor driver, with the assistance of the
engineer. Line engineers normally towed the aircraft for
maintenance purposes only. In addition, the SOP stated:
"Use a marshal (usually the engineer) when manoeuvring for hook
up to the tow bar when it is attached to the aircraft. Do not stand
up to see the hitch point."
The operator's Engineering and Maintenance Procedures Manual
stated that:
"...Prior to push-out operation, the engineer will...(2) Connect
the towbar and towmotor by front or rear connection as
appropriate..."
A ramp driver's licence was valid for a 12 month period. Renewal
was devolved to airline operators by the airport owner and
consisted of a written examination covering rules, procedures,
airfield speed limits and ATC communications and light signals. No
driver refresher training was conducted. Company towmotor drivers
who were qualified to tow aircraft on the ramp were to conduct
towing operations in accordance with their respective company
SOP.
