On 31 March 2016, an Airbus A330-323, registered 9M-MTB and operated by Malaysia Airlines Berhad (Malaysia Airlines), was being prepared and boarded for a flight from Melbourne Airport, Victoria, to Kuala Lumpur, Malaysia. The captain engaged the aircraft’s park brake before carrying out an external inspection of the aircraft. The resulting lit park brake indicator light on the nose landing gear led the aircraft maintenance engineer to assume that the park brake would remain on. Thinking that the aircraft would remain secure, the maintenance engineer removed the main landing gear chocks out of sequence with the relevant procedure and without informing the others in the ground crew. The ground crews did not check the main gear chocks before removing the nose gear chocks to attach the tow tractor to the nose gear. Unaware that no chocks were in place, and out of sequence with the relevant procedure, the captain released the park brake on return to the flight deck. The aircraft rolled back about 3 m and struck the aerobridge. The aircraft’s forward-left door and hinges, and the aerobridge were damaged. There were no injuries.
What the ATSB found
The ATSB found that the ground and flight crew procedures were not well harmonised, leading to reduced cohesion between the crews, and that the tractor operator’s procedures did not match the way tasks were carried out locally. These problems reduced the likelihood that the respective procedures would be followed correctly. In addition, the flight crew and engineers did not explicitly convey their actions and intentions to the others, resulting in a number of missed opportunities to discover the resulting procedural errors.
What's been done as a result
The engineering company, tractor operator and Malaysia Airlines each planned or initiated safety action in response to this occurrence. The engineering company introduced standard procedures and initiated periodic operational safety inspections at all ports. The tractor operator developed a written procedure to incorporate local differences in work practices and improve coordination. Malaysia Airlines reported that it was planning to amend its procedures so that flight crews advise ground crews whenever the park brake is about to be released. As an interim measure, Malaysia Airlines sent A330 flight crews a reminder to communicate with ground crews before releasing the park brake to verify that chocks are in place.
The ATSB stresses the importance of organisations ensuring that ground and flight crew procedures are harmonised to increase the likelihood that potential problems or mistakes are detected before causing harm. It is also important that local variations to procedures are formalised to reduce the risk of the inconsistent completion of tasks, and to improve the organisation’s ability to identify and address potential safety concerns. In addition, the ATSB encourages crews to highlight any procedural problems to their operator in order for them to be reviewed and enhanced as appropriate.
Importantly, when about to perform a key action like removing chocks or releasing the park brake, crews should consider checking with others to identify potential conflicts between tasks. This can reduce the risk of unintentional aircraft movement.
Sequence of events
On 31 March 2016, an Airbus A330-323, registered 9M-MTB and operated by Malaysia Airlines Berhad (Malaysia Airlines), was being prepared and boarded for a flight from Melbourne Airport, Victoria, to Kuala Lumpur, Malaysia. The aircraft had been parked in the bay for several hours following its previous flight, and was secured using wheel chocks under the left main and nose landing gears.
An engineering company provided an aircraft maintenance engineer (AME) and a licenced aircraft maintenance engineer (LAME) to prepare the aircraft for departure. A third company provided a towbarless tractor and driver for pushback. A technician was also refuelling the aircraft using a fuel truck parked under the aircraft’s wing. Ground crews could communicate with the flight crew via a headset.
At 0037 Eastern Daylight-saving Time, the aircraft captain engaged the park brake before disembarking to perform a pre-flight external inspection of the aircraft. The park brake had to be set to check the brake wear indicators and could only be controlled from the flight deck. A closed-circuit television recording showed the captain performing the inspection from 0043 to 0048.
Shortly after the captain checked the main landing gear chocks, the AME removed them from the left main landing gear in preparation for pushback. The AME was aware that this step was not in accordance with the normal sequence for pushback with a towbarless tractor, but thought that the aircraft would be secure because the:
- nose landing gear chocks were installed
- park brake indicator light on the nose landing gear had been on when it was recently checked by the AME, consistent with the brake being engaged (Figure 1).
Shortly after, the tractor driver arrived at the bay and boarded the tractor. The driver prepared the vehicle for docking to the aircraft’s nose landing gear. The tractor driver reported being unable to see whether the main landing gear chocks were in place due to the shadowing under the aircraft.
At 0051:03, the LAME started to remove the nose chocks so that the towbarless tractor could be docked. The AME assisted the LAME and together they finished removing the chocks at 0051:14. Both then moved off under the aerobridge, which was still in use by boarding crews and passengers. The closed-circuit television recording showed the refueller disconnecting the refuelling equipment from the aircraft’s under-wing filler point at about the same time as the nose chocks were removed.
The driver began to move the towbarless tractor into position to engage the nose landing gear at 0051:18. The closed-circuit television recording showed that the park brake indicator light turned off at 0051:21. This aligned with the flight crew’s recollection that the captain released the park brake on return to the flight deck. The captain later reported always doing this, expecting that the ground crews would inform him when it was necessary to apply the brake.
At 0051:27, as the towbarless tractor moved towards the nose landing gear, the aircraft began to move very slowly backwards. The refueller lowered the fuel truck’s lift a few seconds after the aircraft started moving. The towbarless tractor driver did not notice the aircraft’s movement at first. He continued forward and stopped when the tractor made contact with the aircraft’s nose gear tyres, then drove forward for another 3 seconds. This second movement was probably because the driver noticed the increasing distance between the tractor and the aircraft and automatically tried to bring them closer. The driver did not initially recognise that the situation was abnormal.
The aircraft’s slow movement was not immediately obvious to the flight or ground crews. The aircraft stopped after coming into contact with the aerobridge, having rolled backwards about 3 m in 22 seconds. Hearing the noise and realising that the aircraft had moved, the LAME radioed the flight crew to set the park brake. The captain completed this action at 0052:09.
The aircraft’s forward-left door was dislocated by the contact with the aerobridge (Figure 2). The door, hinges, and aerobridge were damaged and there was slight indentation of the fuselage skin forward of the door. There was no major structural damage. There were no injuries.
Source: Melbourne Airport, modified by the ATSB
The engineering company used Malaysia Airlines procedures for ground handling. The procedure for the departure stage of a transit check included a step to remove all of the chocks after the aerobridge is detached from the aircraft. The procedure for pushback stated that ‘Chocks should not be removed from the main-gear until the tractor is fully secured to the nose‑gear’. It did not contain guidance for coordinating with a tractor driver.
Tractor operator procedures
The tractor operator used a set of written procedures as the basis for activities that varied across the organisation depending on local arrangements. Workers were trained according to these local requirements.
The written procedure for pushback with a towbarless tractor showed photographs of the pushback activity that included steps for a ‘walk-around check’. It also included confirming that the:
- ‘main gear [was] chocked’ prior to docking the tractor with the aircraft’s nose wheels
- ‘Chocks should not be removed from the main-gear until the tractor is fully secured to the nose-gear and brakes on [the] tractor set.’
At Melbourne Airport, these steps were omitted in practice, because the tractor operator’s work arrangements there did not include management of the wheel chocks. The procedure did not describe how a driver should coordinate with other ground crews when docking the tractor to the aircraft.
Flight crew procedures
The flight crew procedures included steps to:
- set the park brake before carrying out an external inspection of the aircraft
- check the park brake is set and release it only if the brakes are hot (that is, soon after landing) and chocks are in place
- release the park brake after all aircraft doors are closed, pushback clearance is received from air traffic control and ground crew readiness is confirmed.
The procedures did not provide guidance or instruction on how to coordinate park brake release with ground crews.
- A towbarless tractor has a mechanism that grips and lifts the aircraft’s nose wheels. It cannot be docked with nose landing gear chocks in place. A conventional tractor uses a towbar to attach to the nose landing gear and chocks can be in place at that time.
- Moving an aircraft from its parking position to a taxi position using specialised ground support equipment.
- Eastern Daylight-saving Time (EDT) was Coordinated Universal Time (UTC) + 10 hours.
Explanation of the occurrence
The aircraft’s park brake was set for the captain’s external inspection of the aircraft. The resulting illumination of the park brake indicator light on the nose landing gear led the aircraft maintenance engineer to assume that it would remain set, though this was not confirmed with the flight crew. Thinking that the aircraft would remain secure, the aircraft maintenance engineer removed the main landing gear chocks.
Subsequently, the ground crews did not check the main landing gear chocks before the engineers removed the nose landing gear chocks to dock the towbarless tractor. The tractor operator’s written procedure included a step to check the main landing gear chocks, but in practice, the step was omitted at Melbourne Airport because of a local variation in the way the work was conducted. In addition, there was no corresponding step in the engineers’ procedures. As a result, the absence of main gear chocks remained undetected.
Separately, the aircraft captain was unaware that the docking process was underway and that no chocks were in place. Although the flight crew procedures stated that the park brake should only be released when the wheel brakes were hot (generally only shortly after landing), or after the aircraft doors were closed and with ground crew clearance, the captain released the park brake on return to the flight deck. In the absence of any braking mechanism, the aircraft commenced moving until it struck the aerobridge.
Lessons for effective teamwork
This occurrence highlights the importance of organisations ensuring that ground and flight crew procedures are harmonised to increase the likelihood that potential problems or mistakes are detected before causing harm, and of affected crews applying those procedures consistently. In addition, it is important that local variations to procedures are formalised to reduce the risk of the inconsistent completion of tasks, and improve the organisation’s ability to identify and address potential safety concerns.
Also highlighted is the importance of crews, when about to perform a key action, considering a check with others to identify potential conflicts between tasks. In this instance, such a check before removing chocks or releasing the park brake would likely have reduced the risk of unintentional aircraft movement.
From the evidence available, the following findings are made with respect to the ground handling occurrence involving Airbus A330, registered 9M-MTB and operated by Malaysia Airlines Berhad, which occurred at Melbourne Airport, Victoria on 31 March 2016. These findings should not be read as apportioning blame or liability to any particular organisation or individual.
- The aircraft maintenance engineer removed the main landing gear chocks before the towbarless tractor was secured to the aircraft and out of sequence with the normal operating procedures.
- Consistent with local practices, neither the engineers nor the tractor driver checked that the main landing gear chocks were in place before attempting to dock the towbarless tractor to the aircraft.
- The aircraft captain released the park brake out of sequence with the normal operating procedures.
Other factors that increased risk
- The procedures provided to ground and flight crews by Malaysia AirlinesBerhad and the towbarlesstractor operator did not provide clear guidance or instruction on coordinating activities related to pushback and, in the case of the tractor operator, were informally replaced by local procedures. [Safety Issue]
Safety issues and actions
The safety issue identified during this investigation are listed in the Findings and Safety issues and actions sections of this report. The ATSB expects that all safety issues identified by the investigation should be addressed by the relevant organisation(s). In addressing those issues, the ATSB prefers to encourage relevant organisation(s) to proactively initiate safety action, rather than to issue formal safety recommendations or safety advisory notices.
All of the directly involved parties were provided with a draft report and invited to provide submissions. As part of that process, each organisation was asked to communicate what safety actions, if any, they had carried out or were planning to carry out in relation to each safety issue relevant to their organisation.
The initial public version of these safety issues and actions are repeated separately on the ATSB website to facilitate monitoring by interested parties. Where relevant the safety issues and actions will be updated on the ATSB website as information comes to hand.
Coordination of activities related to pushback
The procedures provided to ground and flight crews by Malaysia Airlines Berhad and the towbarless tractor operator did not provide clear guidance or instruction on coordinating activities related to pushback and, in the case of the tractor operator, were informally replaced by local procedures.
ATSB Safety Issue: AO-2016-028-SI-01
ATSB Safety Advisory Notice: AO-2016-028-SAN-006