Description

On 18 June 2021, a Boeing 787-8 (G-ZBJB) being operated by British Airways was being loaded for a cargo flight at Heathrow in normal day visibility whilst a line engineering team carried out checks required to permit despatch with a fault affecting the normal function of the Nose Landing Gear (NLG) bay doors. The check required cycling the landing gear with the locking pins inserted so that only the bay doors cycled but when this was done, the nose gear retracted and the front of aircraft dropped to the ground causing significant damage to the airframe and minor injuries to the First Officer and one of the cargo loading team.

The front of the aircraft following inadvertent retraction of the nose landing gear. [Reproduced from the Official Report] 

Investigation

An Investigation was carried out by the UK AAIB. Relevant data were obtained from the CVR in respect of the action of the line maintenance team who had attended the aircraft to carry out the required check of the reported landing gear bay doors fault which consisted of a LAE and two Mechanics. One of the Mechanics was experienced on the 787 aircraft and had extensive experience of working with the LAE. The other had been seconded from the Cabin Excellence Team, which was to be absorbed into the line maintenance task to pass on knowledge and experience of cabin and seat maintenance whilst “unofficially” gaining knowledge and experience of the scope of line maintenance.

What happened

The aircraft was undergoing a corrective maintenance task to allow the deferment of three NLG Solenoid faults in accordance with the Despatch Deviation Guide. This required cycling of the landing gear system to check a suspected fault in the operation of landing gear bay doors which could be done without the gear legs moving provided the locking pins were inserted. 

The LAE needed to be on the flight deck to select the landing gear up and the time available was limited so he delegated the fitting and checking of the landing gear pins to the two Mechanics, one of whom was experienced and trusted by the LAE who had previously worked with him. He supervised the Mechanics remotely from the flight deck and communicated with the experienced one via a headset. The experienced Mechanic asked his colleague to fit the NLG pin because the steps needed to access the NLG bay were not immediately available and he was tall enough to do it without steps. The experienced Mechanic stated that he had pointed to where the pin should go, monitored the fitting of it and “checked it by listening, looking and pulling the flag”.

However, the downlock pin was inadvertently inserted into the downlock link assembly apex pin bore instead of the downlock pin hole (the two adjacent holes are visible on the illustration below) so the nose gear retracted when the system was operated. 

The NLG downlock pin incorrectly fitted to the apex pin bore (left) and an example of the correct location of the pin for comparison (right). [Reproduced from the Official Report]

The underside of the aircraft forward fuselage and the front lower part of both engine cowlings sustained significant damage and the former movement resulted in the immediate loss of AC power to the aircraft as the ground power cables were crushed. Minor damage was also caused to Door 2L and to the aft cargo door.

Once the accident had occurred, the airport response was assessed to have been problematic in respect of its categorisation under the Airport’s “Emergency Orders”. 

Why it happened  

The design of the aircraft nose landing gear downlock assembly had already been identified by Boeing as presenting an opportunity for error when inserting the NLG locking pin, with two holes located so close together that the pin could be inadvertently inserted in the incorrect location. Initially a SB and later an AD had been issued to eliminate the risk of NLG locking pin insertion into the wrong hole but the required action had not yet been taken on G-ZBJB. 

It was evident that the limited space available within the NLG bay and the location of both the correct pin hole and the adjacent one above their heads would have made it difficult to positively indicate the correct pin location, especially without prior access to a picture like the one in the 787 AMM which at the time was not accessible on the iPads issued to line maintenance personnel. The experienced Mechanic also reported having attempted to check everyone was clear of the aircraft before the LAE operated the system but this visual check was ineffective because of the restricted view from close to the NLG but the possibility the aircraft nose could drop was not considered. The aircraft operator also did not have any procedures to cover potential maintenance-related hazards during loading or passenger boarding. 

In respect of the pin insertion error which occurred, the possibility of installing the NLG downlock pin in the incorrect position pending the planned modification, an attempt to raise awareness was made using the Technical News “read and sign process” (see the illustration below). However, as all three maintenance personnel had signed to say they had read the item concerned five months before the accident, it was suspected that the amount of information communicated in this way was too great for all of it to be remembered.

The Technical News item on correct fitting of the 787 NLG downlock pin. [Reproduced from the Official Report]

Safety Action taken as a result of the Accident was noted as having included the following:

British Airways has:

• Implemented the delayed AD and SB on all its 787 aircraft
• Improved the process for assessing SBs and ADs by developing appropriate organisational structures to identify and manage health and safety risks more effectively in the Technical Document Response process. 
• Commenced adoption of an SMS within the maintenance organisation following the CAA rulemaking announcement requiring introduction of an SMS into Part 21 and Part 145 activity with approval targeted the end of 2022. 
• Provided line maintenance personnel with access to all manufacturers’ technical data, documents and manuals via their already-issued iPads.
• Introduced a new software application for communicating technical updates which includes improved filtering and prioritisation and requires that each page of every article is displayed before it can be signed. 

Heathrow Airport Limited has:

• Stated its intention to amend the airport Emergency Order (EO) Action Cards for each stakeholder to include a requirement for each Business Unit to make an individual assessment of the incident categorisation and communicate that to the RFFS Commander. 
• Stated its intention to amend the airport EO Action Card for the RFFS Commander to include any consideration of a change in categorisation in liaison with other stakeholders. 
• Stated that all airport EOs will in future include a cordon requirement in all categories for transmission to the Campus Security Manager    

The Conclusion of the Investigation was formally recorded as:

The aircraft NLG retracted on the ground when the landing gear selection lever was selected to up as part of a maintenance procedure. The NLG downlock pin had inadvertently been inserted in the downlock link assembly apex pin bore instead of the downlock pin hole. When the nose of the aircraft struck the ground, significant damage was caused to the lower front section of the aircraft and minor injuries to the co-pilot and a member of the cargo load team. The design of the aircraft nose landing gear downlock assembly created an opportunity for error when inserting the NLG locking pin, with two holes located so close together that the pin could be inadvertently inserted in the incorrect location. There were powerful auditory and tactile cues that could easily mislead someone to believe the pin was correctly inserted even when it wasn’t and there were no strong visual indications to distinguish between the correct and incorrect placements. The determination of the risk of incorrect installation of the NLG downlock pin in the manufacturer’s SB and the regulator’s AD did take account of the design of the B787 NLG and the associated probability for error. The operator’s process to embody ADs and SBs considered flight safety, airworthiness and the AD’s ‘effect’ in enhancing safety, but there was no documented evidence that health and safety risks had been fully considered. Had these risks, that were clearly highlighted in the AD and SB, been given greater significance by the operator during the embodiment process, the priority of the modification may have been escalated and avoided the decision to defer implementation to the end of the compliance period. 

The Final Report was published on 3 November 2022. No Safety Recommendations were made.

Related Articles

• Line Maintenance
• Landing Gear
• Service Bulletin (SB)
• Airworthiness Directive (AD)
• Aircraft Maintenance Manual (AMM)
• Post-Incident Airport Operations
• Safety Management System
• Risk Mitigation