The aircraft was on its first flight after replacement of the Landing Gear Control Module (LGCM), in response to a reported defect, during a scheduled A Check. The AAIB say:
After retracting the landing gear following takeoff from Heathrow, the crew were unable to move the landing gear lever from the ‘UP’ to the ‘OFF’ position, as it had become jammed in the ‘UP’ detent. The crew elected to return to Heathrow and, in accordance with 747 Flight Crew Operations Manual Non-Normal Checklist procedures, the landing gear was lowered using the alternate extension system.
BA B747 G-CIVX on Approach with Only Nose and Body Landing Gear Deployed (Credit: Wael Al-Qutub)
The aircraft landed safely, with only the nose and body landing gear deployed.
The aircraft stopped on Heathrow’s runway 27R, which was unavailable for about an hour until the aircraft was secured and towed off the runway.
The landing gear…is mechanically commanded and hydraulically actuated. There is a three-position handle in the cockpit with the following spring-loaded detents: DN, OFF and UP. The handle must be pulled outwards against spring pressure to enable it to be moved to another position. The handle is part of the LGCM.
B747 Landing Gear Control Module: Showing Handle and Control Rod (Credit: Boeing via AAIB)
The handle is connected to a control rod, which in turn is connected to a quadrant, and attached to the quadrant is a cable that runs to the wing gear selector valve quadrant located in the right hand body gear wheel well. Another cable runs from the wing gear selector valve quadrant to the nose/body gear selector valve quadrant located in the left‑hand body gear wheel well.
The quadrant in each wheel well is connected to a selector valve by a mechanical lever. When a replacement LGCM is installed, it is a requirement in the Aircraft Maintenance Manual (AMM) to insert a rig pin in the selector valve quadrant.
B747 Wing Gear Selector Valve Installation: note rig pin (Credit: Boeing via AAIB)
This video shows typical landing gear functional checks to illustrate how the wing and body gears retract and deploy:
The Prior Maintenance
During the A Check:
The night shift had raised the task cards for the removal and re-rigging of the original LGCM; these cards included the tasks of fitting the rig pin in the selector valve quadrant, function checks and a duplicate inspection. The night shift staff removed and re-rigged the LGCM, but did not have time to compete the function checks, and the task cards were left uncertified.
The re-rigged LGCM failed the function check made by the day shift, and the day shift then fitted a replacement serviceable LGCM. The task cards raised by the day shift staff for replacing the LGCM did not contain a task for the fitment and removal of the rig pins in the selector valve quadrants. The task cards raised by the night shift were used to certify the function checks.
Three day shift engineers were involved in the fitting of the LGCM. They had the relevant sections of the AMM and the applicable Temporary Revision (TR) to the AMM, generated by the operator to provide additional information on the task. The engineers became focused on achieving the correct adjustment and hence were using the TR (which did not specify the need to fit the rig pins).
A consequence of omitting to use the rig pin was the need to use five shims to enable the LGCM to be fitted to the instrument panel; three shims are more typical for a correctly rigged system.
One of the engineers, who was positioned near the quadrant in the right-hand wheel well, noticed that the rig pin was not fitted and that the quadrant was moving (by inputs from another engineer in the cockpit). He was concerned that he might be injured, and took a planned break that was overdue.
It’s not clear in the AAIB report if the engineer had intended to query / report the omission or how long the break was overdue.
Analysis and Conclusions
It was concluded that jamming was due to the rig pin not being inserted during maintenance, which led to “additional and unnecessary shims being used to rig the landing gear lever”.
The operator’s internal investigation identified the following causal factors:
The distraction of the engineer when he saw the quadrant move, and he took his break
Deficiencies in the operator’s task card system
The omission of the need to fit the rig pin in the operator’s TR for this task
An inadequate handover between the night shift and the day shift
Safety Actions
BA has taken a number of actions according to the AAIB including:
Updating the TR so that technical management are consulted if more than three rigging shims are used for this task and to include a requirement to fit rig pins and to check that the rig pins can be inserted freely once function checks are completed
Holding staff briefings to reinforce the requirements to adhere to handover procedures
Publishing a bulletin to highlight this incident, including the distraction aspect
Introduction of additional skills training in task card generation.
Other Resources
Aerossurance has previously looked at these associated topics:
UPDATE 24 June 2018:B1900D Emergency Landing: Maintenance Standards & Practices The TSB report posses many questions on the management and oversight of aircraft maintenance, competency and maintenance standards & practices after this serious incident. We look at opportunities for forward thinking MROs to improve their maintenance standards and practices.
UPDATE 25 August 2018: Crossed Cables: Colgan Air B1900D N240CJ Maintenance Error On 26 August 2003 a B1900D crashed on take off after errors during flying control maintenance. We look at the maintenance human factor safety lessons from this and another B1900 accident that year.
UPDATE 31 May 2019: The Portuguese accident investigation agency, GPIAAF, issued a safety investigation update on a serious in-flight loss of control incident involving Air AstanaEmbraerERJ-190P4-KCJ that occurred on 11 November 2018. The aircraft was landed safely after considerable difficulty, so much so the crew had debated ditching offshore. GPIAAF conformed that incorrect ailerons control cable system installation had occurred in both wings during a maintenance check conducted in Portugal.
Misrigged Flying Control Cable, Air Astana Embraer EJ-190 P4-KCJ (Credit: GPIAFF)
GPIAFF note that: “By introducing the modification iaw Service Bulletin 190-57-0038 during the maintenance activities, there was no longer the cable routing and separation around rib 21, making it harder to understand the maintenance instructions, with recognized opportunities for improvement in the maintenance actions interpretation”. They also comment that: “The message “FLT CTRL NO DISPATCH” was generated during the maintenance activities, which in turn originated additional troubleshooting activities by the maintenance service provider, supported by the aircraft manufacturer. These activities, which lasted for 11 days, did not identify the ailerons’ cables reversal, nor was this correlated to the “FLT CTRL NO DISPATCH” message.”
GPIAFF comment “deviations to the internal procedures” occurred within the maintenance organisation that “led to the error not being detected in the various safety barriers designed” in the process. They also note that the error ” was not identified in the aircraft operational checks (flight controls check) by the operator’s crew.”
Aerossurance worked with the Flight Safety Foundation (FSF) to create a Maintenance Observation Program (MOP) requirement for their contractible BARSOHO offshore helicopter Safety Performance Requirements to help learning about routine maintenance and then to initiate safety improvements:
Aerossurance can provide practice guidance and specialist support to successfully implement a MOP.
Aerossurance has extensive air safety, aircraft design and certification, airworthiness, human factors and safety analysis experience. For practical advice you can trust, contact us at: enquiries@aerossurance.com
