On 14 August 2018, an Airbus A320 (VH-FNP) being operated by Virgin Australia Regional Airlines on a scheduled passenger flight from Perth to Christmas Island with an augmented crew due to the length of the flight duty period began its departure from Perth in day VMC with the main landing gear ground locking pin sleeves still installed after removal of the their locking pins. One sleeve then fell out, unseen, during pushback and the other fell out, again unseen, during takeoff. Reports of FOD on the runway eventually led to the location of one sleeve and the other was subsequently recovered from the apron. The intended flight was completed without further event and the aircraft was subsequently found to be undamaged.
An Investigation was carried out by the Australian Transport Safety Bureau (ATSB).
It was noted that prior to passenger boarding, the aircraft had been towed by ground handling personnel from the domestic apron to its departure gate at the international terminal. Prior to this tow, an ‘apron engineer’ employed by the airline’s aircraft maintenance organisation (AMO) had fitted the Landing Gear Ground Locks (LGGL) which, in the case of the main landing gear on this aircraft type, consist of a sleeve which is secured in position by an attached pin (see the illustration below). This engineer then acted as the aircraft brake operator for the tow. Shortly after the tow had been completed, he left the aircraft having been instructed to supervise the refuelling of another aircraft. At this point, he expected to be able to return after the refuelling task to also supervise the refuelling of the A320 and to remove the LGGLs at that time. Whilst he was away from the aircraft, other airline AMO engineers (referred to from now on as the ‘onboard engineers’) were working on the flight deck of the A320 to rectify an avionics defect and being assisted by another company engineer who had been assigned as a matter of routine to travel with the aircraft to Christmas Island. The ‘apron engineer’ who had ridden the brakes during the tow was aware that the rectification work was to take place and that there was a possibility that if it was not successful, an alternative aircraft may have to be found to operate the flight.
An operating crew consisting of a Captain and a First Officer were rostered for the flight and the Captain decided to act as PF for the first flight. They were to be accompanied by an augmenting crew member, who in this instance was a Training Captain. No specific pre-flight duties were specified for an augmenting crew member but it was common practice for them to carry out the external pre flight check. It was noted that the aircraft was scheduled to continue from Christmas Island to the Cocos Islands before returning to Perth and since enhanced pre-flight preparations were required, delegation of the external check to the augmenting crew member would represent a good use of resources.
The flight crew arrived at the aircraft approximately an hour prior to the scheduled departure time but were initially unable to gain access to the flight deck because of the rectification work and they were advised that it was likely to be another half hour before they could enter the flight deck. The augmenting crew member then carried out the external check, observing that the LGGLs were still fitted with the flags showing. He reported having considered removing them but that he had concluded that he could not do so safely and so on completion of the check, he had advised the Captain accordingly. The Captain subsequently stated that he had “assumed” that LGGL removal would occur during normal departure procedures.
On realising that he would not be able to get back to the A320 to supervise refuelling, the ‘apron engineer’ who had been involved in the tow phoned one of the ‘on-board engineers’ and asked him to take over the task of preparing the A320 for departure, including supervising refuelling. This refuelling subsequently took almost half an hour and was completed 20 minutes prior to schedule time of departure.
By the time refuelling had finished, the driver tasked by the contracted ground handling agent Swissport was present in his tug which was attached to the front of the aircraft and the Swissport Dispatcher assigned to the departure was sitting in the tug with him. Hold loading had been completed and passenger boarding was about to commence. However, whilst waiting in the tug, the driver then noticed that the locking pins and their associated flags were still installed which he stated he had “considered unusual”. He reported having attempted for around 10 minutes thereafter to contact the ‘Aircraft Movements Coordinator’ (AMCO) by radio to request an engineer to inspect the pins but when he had been unable to do so with only 7 minutes to go until departure, he had decided to remove the pins himself. Unfamiliar with the relatively unusual LGGL system on the A320, he had not also removed the associated locking sleeves. He placed the three flagged pins in his vehicle and then boarded the now fully loaded aircraft to get the load sheet countersigned by the Captain. The Dispatcher, in headset communication with the flight crew, then confirmed that “all doors and panels were secured and that the aircraft was clear to push back”. Neither of them mentioned to the flight crew that the tug driver had removed the flagged locking pins from the landing gear.
As the aircraft push back began, one of the LGGL sleeves fell unnoticed from the aircraft onto the taxiway and then, about 10 minute later, a second sleeve fell from the aircraft onto the departure runway as the aircraft got airborne, again unnoticed. A number of reports of FOD on both runways and taxiways then began to occur. After a report from a landing aircraft crew to ATC of FOD on the runway about half an hour after the A320 had taken off, a runway inspection was carried out by an airport operations officer but no FOD was found. However, ten minutes later, another similar report led to a second runway inspection by a different operations officer who located one of the LGGL locking sleeves next to the runway PAPI and almost an hour later, the second LGGL sleeve was found on the apron. The A320 crew, by this time on the descent into Christmas Island, were advised of the findings and asked to check the flight deck stowage compartment to see if the LGGL pins and sleeves were on board and found that they were not. As a precaution against possible landing gear damage, the gear was lowered a little earlier than usual in case additional time was required to respond to any abnormal indications but the remainder of the flight was uneventful and a subsequent inspection by the engineer travelling with the aircraft found no evidence of any aircraft damage.
The A320 LGGL System
Contrary to the conventional LGGL systems in which all three gear legs are locked in position only by locking pins, in the case of the A320, locking is achieved by fitting hinged ‘sleeves’ in the locking position and then securing the sleeves in position with locking pins (which look like the pins more usually used on their own as ground locks).The locking pins are fitted with the usual red flags. Two different LGGL systems of this type are used on A320s with that on the aircraft involved using the sleeves to secure the landing gear strut position (see the illustration below) rather than the landing gear door actuating cylinder.
The conventional ‘simple’ flagged-pin system used on the nose landing gear and the two similarly-flagged sleeve-and-pin systems used on the main gear would normally be a set specifically assigned to the aircraft. When not fitted, this would be kept on board the aircraft in a designated stowage on the flight deck where their presence could be confirmed prior to commencing a flight. Each main gear sleeve is supposed to be painted red and attached to the corresponding pin to which the red flag is attached by means of a wire lanyard. However, it was found that in this case, neither sleeve was attached to its flagged pin, making it easy for anyone unfamiliar with the aircraft type to remove only the flagged pins from the main gear. One of the sleeves in this case was also missing most of its red paint (see below). It was established that the absence of the lanyards had not been reported prior to the investigated event and also that the same lanyards were also missing from the main LGGLs on two other A320s in the operators fleet.
The A320 landing gear strut locking system on the aircraft involved. [Reproduced from the Official Report]
The main landing gear locking sleeves and flagged pins fitted to the aircraft involved. [Reproduced from the Official Report]
Procedures for LGGL Use
The extent to which procedures for the use of LGLLs during towing operations and the allocation of the associated responsibilities were documented for use by those involved was reviewed:
- The Manual detailing the operator’s ‘Approved Maintenance Program’ (AMP) contained a comprehensive description of maintenance procedures for the aircraft operator’s Aircraft Maintenance Organisation (AMO) personnel but did not include any reference to towing procedures or the installation or removal of the LGGL.
- The A320 AMM described the maintenance procedures for the A320 as specified by Airbus and although it stated that “safety devices (LGGL) were to be installed on landing gear prior to towing” it made no reference to their removal following a tow.
- The ‘Virgin Group Operations Manual: Airport Airside Operations Manual’ (AAOM) provided instructions for towing Airbus A330 and Boeing 737 aircraft which included a requirement to install and remove LGGLs and that the person responsible for ensuring that this occurred on these aircraft types was the person designated as aircraft brake operator for the tow. This Manual did not include any mention of towing procedures for A320 aircraft or the related responsibility of the brake operator. Its only mention of the LGGLs on the A320 was in a section on dispatch procedures for A320 and Fokker 100 aircraft which stated that “removal of landing gear pins was the responsibility of the flight crew and engineering”.
- The operator’s applicable ‘Line Maintenance Procedures’ (LMP) dated 11 September 2017 stated that “towing should be conducted in accordance with the AMM”. There was no reference to the installation or removal of LGGLs as part of towing and a section entitled ‘Removal of locking and safety devices’ contained nothing except the word ‘Reserved’. It was found that a previous version of the LMP dated 9 September 2016 had included a description of the tasks involved in towing aircraft, but this did not include “a step for removing LGGL after a tow”. It did have a section on ‘Removal of Locking Devices’ which stated that:
- The Captain was responsible for ensuring that all ground locks were removed prior to flight and must confirm with the First Officer that locking pins had been removed and stowed on board the aircraft.
- Authorised aircraft maintenance engineers must remove locks and stow them on the aircraft.
- The Dispatcher would provide an additional check during the pre-dispatch walk-around to ensure all locks had been removed.
Given the above findings, the Investigation concluded that “there were no specific procedures for removing LGGL from the operator’s A320s after a positioning tow”.
LGGL Procedures as Understood by Engineers
In the absence of any explicit requirements relevant to the pre-departure situation in this case, the Investigation examined the engineers’ understanding of the process for installing and removing LGGL.
The ‘on-board engineer’, who had taken over responsibility from the ‘apron engineer’ who had originally anticipated covering the whole pre-departure task but had been unable to do so after going to oversee refuelling of another aircraft, stated that the normal sequence after towing an aircraft onto the departure bay was for the engineer to remove the LGGL and stow them on board on completion of the tow. However, the ‘apron engineer’ "said it was approved practice for engineers to leave pins in place after towing an aircraft, particularly if the aircraft was likely to sit for a while or may be unserviceable and towed off the bay” and that in such circumstances, engineers would leave the LGGL installed after a tow and remove them only in conjunction with subsequent refuelling.
It was found that there had recently been changes to the operator’s pre-flight dispatch duties which affected the pre departure responsibilities of engineers. Prior to these changes, engineers from the airline’s AMO were responsible for dispatch including an external inspection which would include the removal of any LGGLs found to be still installed. Under the new arrangements which had been in place for almost three months, a contractor (Swissport then Aerocare) had taken over responsibility for dispatch duties. AMO engineers advised that they had continued to conduct informal external checks after this transfer of dispatch duties despite the absence of any requirement to do so. The on-board engineer advised that he did not perform such a (now entirely optional) external check after supervising the refuelling. It was also not possible to establish whether the phone call in which transfer of engineer oversight of refuelling was agreed had included any specific mention of the fact that the LGGLs were still installed. However, it was found that the operator’s AMO “did not have documented procedures or training relating to the handover process between engineers”.
Flight Crew Responsibilities in Relation to LGGL Removal
The pre-flight procedures and responsibilities for the operator’s A320 flight crew were described in the A320 FCOM and the A320 QRH. The preliminary flight deck pre flight check before every flight was found to require that a check should be made to confirm that the LGGLs and pitot tube covers were on board and stowed. The QRH assigns this duty to the PM although the flight crew involved indicated that the check was normally done by the pilot assigned to carry out the external pre flight check as they left the flight deck for that purpose since the LGGL stowage compartment was in a position which made the required check difficult to do whilst in a pilot seat. It was, though, apparent that in practice, the stowage compartment check “was not necessarily dependent on external check, although the crew perceived the tasks were normally performed together”. The external pre flight check was, however, found to explicitly include checking that “the nose, left main, and right main landing gear safety pins have been removed”.
It was noted that the company ‘Flight Operations Policies and Procedures Manual’ (FOPPM) applicable to all aircraft operated by the airline described additional procedures to be carried out if one or more LGGLs was found to still be installed during an external pre-flight check. These required that in such circumstances, the Captain must:
- direct that the LGGLs are removed prior to taxiing.
- confirm the LGGLs have been removed by the presentation of the removed locks/pins by an authorised person from an appropriate position on the ground.
- acknowledge (in the form of a ‘thumbs up’ sign) that they are satisfied that all locking devices have been removed (this signal may alternatively be given by the First Officer).
In the case of the investigated departure, it was the augmenting crew member who had performed the external check and, on re-boarding the aircraft, he had told the Captain that the LGGLs were still installed. No evidence was found that the latter had subsequently “directed or confirmed the removal of the LGGLs as documented in the FOPPM” but it was also noted that the second ‘challenge and response’ item on the ‘Before Start’ Checklist was “Gear Pins and Covers Removed”.
The Circumstances Leading to Despatch with the Gear Ground Locks Not Fully Removed
It was considered that the failure to properly remove the main gear LGGLs had been the consequence of a number of factors:
- Maintenance organisation procedures did not define installing and removing LGGL as a maintenance activity, so there was no requirement to record these activities in the Aircraft Technical Log.
- It was not possible to be certain that the telephone communication between the ‘apron engineer’, who was aware that the LGGLs were still fitted to the aircraft, and the ‘on board engineer’ to whom he had passed the responsibility of overseeing refuelling, had included reference to the need to remove them. Although no longer required perform a pre-departure external check after a ground handling contractor had been engaged by the aircraft operator to oversee all aspects of dispatch, it was noted that engineers sometimes (but not in this case) had continued to informally conduct such a check.
- A320 procedures for ground handlers under the new contractor required the Dispatcher to perform a walk-around check prior to departure and stated that all ground handlers should “be aware” of landing gear pins with the Dispatcher required to “check that landing gear pins have been removed during the walk-around”. The procedures stated that any abnormalities (such as unexpected pins) must be reported to the aircraft Captain immediately after the walk-around. However, no training or familiarisation in the ‘non-standard’ A320 landing gear ground lock system had been provided.
- Having been unable to contact the ‘Aircraft Movements Coordinator’ by telephone to report that he could see the flagged pins still installed, concerned that he should not contribute to a delayed departure and being familiar with the removal of ‘conventional’ gear ground lock pins from Boeing 737 aircraft “to assist the engineers” and under their supervision, the pushback tug driver had assumed that A320 main gear locking was similar. The Dispatcher was aware of and concurred with the tug driver’s action to remove (only) the (flagged) pins from the A320 landing gear.
- The fact that it was possible to remove the pins which secured the main gear LGGL sleeves in position without also removing the sleeves was due to the fact the wire lanyards which should have attached the flagged pin to its corresponding sleeve were missing from both main gears.
- The decision to remove the LGGL pins and not contact the flight crew was contrary to ground crew general procedures and training. The pushback driver reported that he did not consider contacting the flight crew. It was noted that there had been several opportunities for both the pushback driver and the Dispatcher to communicate with the flight crew throughout the pre-flight sequence and there was no technical barrier to this.
- The flight crew’s delayed access to the flight deck had disrupted the normal check of the LGGL stowage because the external check was conducted before the flight crew were able to access the flight deck and also because although the augmenting crew member who had carried out the external check had noted that the LGGL were still in place, it was the PM First Officer who would normally have begun his pre flight checks by carrying out that check. The last chance to detect the incomplete removal of the LGGLs was the explicit check to ensure that that they were in the flight deck stowage but did not occur in response to the corresponding challenge during the ‘Before Start Checks’.
A Previous Similar Event at Perth involving Virgin Australia Regional Airlines
It was noted that on 12 April 2016, one of the same operator’s Fokker F100 aircraft had departed from Perth with its ‘conventional’ landing gear pins fitted after a similar failure to remove them after towing to the position where passenger boarding had taken place and an air turn-back had been made when the gear could not be retracted after takeoff. The operator’s internal investigation found that the Captain had seen that the pins were fitted and had “assumed that they would be removed prior to departure”. The engineer who conducted the required pre-dispatch external inspection (a responsibility since transferred to the ground handling contractor) had not noticed that the pins were fitted. This investigation led to a recommendation that the operator’s maintenance organisation “consider making the installation and removal of gear pins an action that requires a maintenance log entry” but this was not actioned and instead it was agreed that a new ‘Aircraft Readiness Log’ would be introduced in which ground lock fitting and removal would have to be recorded and such entries signed for. This agreed action had still not been taken over 2 years after the F100 event had occurred but following the investigated A320 event, the new log was introduced on 8 October 2018.
The formally documented Findings of the Investigation were recorded in the form of five Contributory Factors as follows:
- The handover of pre-flight engineering duties between engineers did not effectively communicate the requirement to remove landing gear ground locks (LGGL), contributing to the on-board engineer having no expectation of any further requirement to perform additional checks or tasks relating to the exterior of the aircraft.
- There was no formal documentation regarding when LGGL pins should be removed following a positional tow. The absence of a formal process contributed to the LGGL remaining in place throughout the preparation of the aircraft and the on-board engineer having no expectation that the LGGL were still installed when he supervised the refuel.
- The normal pre-flight sequence for the flight crew was disrupted due to maintenance work on the flight deck and delegation of the exterior walk-around check. This contributed to the flight crew not identifying that the LGGL were missing from the stowage compartment on-board the aircraft.
- The operator did not have a procedure for making maintenance log entries when LGGL were installed and removed. The maintenance log entry relating to LGGL would have provided another opportunity for the flight crew and the engineer to become aware that the LGGL had not been removed and stored on-board the aircraft before flight.
- Rather than inform an engineer or pilot as per procedures, the pushback driver removed the LGGL pins from the landing gear sleeves before pushback. However, as the lanyards attaching the pins to the sleeves was missing and the pushback driver did not understand the LGGL locking mechanism, he removed the pins and not the sleeves.
The Safety Message drawn from the Investigation was that “it had highlighted how a number of relatively small errors and/or omissions, associated with separate functional areas, can combine to potentially affect flight safety (when) in this case, the identification and rectification of any one factor would probably have significantly reduced the likelihood of the occurrence developing”. It was further observed that “while all persons working in and around aircraft have specific roles, they also have a responsibility to notify the operating crew about any concerns they may have with the aircraft since it is imperative that any concerns are assessed and rectified by appropriately qualified personnel before flight”.
Safety Action taken by Virgin Australia Regional Airlines following the event and known to the Investigation prior to its completion was noted as having included the following:
- The previously agreed but not implemented ‘Aircraft Readiness Log’ and associated procedures has been introduced.
- Flight crew have been instructed to use a standardised method for the stowage of an aircraft’s LGGL pins and sleeves in the stowage compartment provided such that the flag ends are partially exposed, to facilitate easier detection of their presence during pre-flight checks.
- Ground Handlers have been reminded that they are not permitted to remove LGGL pins and that if they observe them still installed during their pre-departure walk round or prior to an imminent pushback, they must instead report this to either the pilot-in-command or to maintenance personnel.
The Final Report was released on 11 September 2019. No Safety Recommendations were made.