On 23 March 2019, an Airbus A320 (HA-LPL) being operated by Wizz Air which was fully loaded for a scheduled passenger flight from Bristol to Katowice was about to be pushed back from its stand in normal night visibility by a 'towbarless' tug when a significant jolt was apparent to the flight crew. The pushback did not commence and after the aircraft nose leg was found to have sustained impact damage, the aircraft was declared unfit to be operated and the occupants were disembarked.
An Investigation was carried out by the UK AAIB. It was confirmed that the nose wheel steering bypass pin had been installed and in preparation for the required pushback, the TLD 200MT lift tug had been “aligned with the aircraft nose landing gear main forging”. The tug driver was undertaking his first pushback in the model and type of tug involved and was being directly supervised by a trainer seated next to him in the tug cab. As the tug was being moved forward using its laser guidance system and joystick and had reached the point where its ‘paddles’ close around the nose wheels, the trainer observed the nose landing gear moving and then reported having heard a bang. The driver immediately stopped the procedure and applied the tug brakes and on inspecting the tug paddles found that the one on the aircraft left side “had contacted and damaged the nut on the torque link centre pivot” and that there was a corresponding witness mark on the paddle.
A detailed investigation of the event was carried out by the ground handling company involved. This established that the nose landing gear movement seen by the trainer during the attachment process had been due to the tug paddle making initial contact with the edge of the torque link nut and that as the paddle then closed further under hydraulic force, the edge of the nut had failed causing the paddle to slip past it with a jolt and a bang as heard by both the flight crew and the trainer.
It was evident that the ‘pick up’ of the aircraft was predicated on the engagement of the tug paddles and that this required a precise longitudinal alignment of the tug with the aircraft nose wheels before pick up was attempted. It was found that the aircraft had been parked with its nose wheels between 10° and 15° off-centre which would be “unremarkable in most circumstances” but that in this case, the position of the wheels relative to the tug was important and the laser guidance system should have been aligned with the nose wheel rather than the nose landing leg as had actually occurred in this case.
It was noted that the tug had an automated positioning system to enable its correct alignment with an aircraft which required that the correct aircraft type is first selected from a menu. This system is then able to detect if the aircraft type approached is not the one selected and in that case, it will not allow the procedure to continue but that it does not prevent the paddles from closing on a correctly selected aircraft type based on incorrect (offset) nose wheel alignment because this is not detected.
It was also noted that the driver involved had considerable experience of aircraft push back using conventional tow bar tugs and had already been trained on a similar TLD 100E towbarless tug prior to his first experience of the TLD 200MT under supervision of a fully qualified ramp trainer.
Although the way in which the damage to the aircraft had been caused - incorrect alignment of the tug lifting paddles - was established, the Investigation concluded that “it is not clear why the event occurred” although it was “possible that a momentary lapse in concentration led to the system being aligned to the nose leg rather than the nose wheels”, an error which it was considered would have been “likely to have gone unnoticed because the 10° to 15° offset of the nose wheels was not significant enough to indicate a problem”. It was further observed that “aligning with the nose wheels is vital” when pushing back with towbarless tugs, since lining up instead with the nose gear leg can “lead to misalignments of up to 25 cm” and such misalignment may then cause “significant damage to the components on the lower articulated part of the nose landing gear on this and many other aircraft types”.
Safety Action taken by the ground handling contractor involved as a result of the investigated event was noted as having included the following:
- Towbarless tug training now specifically emphasises the need for the tug to be aligned with the nosewheels before attachment occurs.
- Pushback crews have been briefed to be more aware of the importance of the nosewheel position and have been asked to make the aircraft crew aware that, where possible, the aircraft should be parked with its nosewheels aligned with the fore-axis of the aircraft.
- As the A320 has been identified as potentially the aircraft type most susceptible to nose landing gear damage when the TLD 200MT tug is used, to the extent possible, either a conventional tow bar and tug or the TLD 100E towbarless tug will now be used with this aircraft type.
The Final Report of the Investigation was published on 10 October 2019. No Safety Recommendations were made.