What happened
On 30 January 2016, a Boeing 747-436, registration G-CIVX, departed from London Heathrow Airport on a commercial passenger flight. During the flight, after the crew retracted the landing gear, they noticed the landing gear lever felt unusual. Upon attempting to move the lever from the up position to the off position, the crew discovered it was jammed in the up detent.
Following consultation with ground engineering staff, the crew decided to return to Heathrow. To ensure a safe arrival, the crew utilized the alternate extension system. This procedure successfully deployed the nose and body landing gear, though the two wing landing gear remained undeployed. The aircraft landed safely, and there were no injuries to the 17 crew members or 2ng3 passengers on board.
The investigation
An investigation by the AAIB focused on the maintenance performed during a recent 'A' Check. This maintenance involved replacing the Landing Gear Control Module (LGCM), which houses the landing gear lever.
Investigators found that the LGCM was mechanically jammed in the up position and required excessive force to move to other positions. The investigation revealed that during the replacement of the LGCM, the maintenance team failed to insert a required rig pin into the selector valve quadrant. This omission led to the use of five shims to fit the LGCM to the instrument panel, whereas a correctly rigged system typically requires only three.
Review of the maintenance records showed that the night shift had prepared task cards that included the rig pin requirement, but they did not complete the function checks before the shift ended. The day shift engineers, working from a Temporary Revision (TR) that lacked the specific instruction for the rig pins, completed the installation. A critical distraction occurred when an engineer, concerned about potential injury from a moving quadrant, took an overdue break, leading to the oversight.
Findings
- The landing gear lever jam was caused by the omission of a rig pin in the selector valve quadrant during the LGCM replacement.
- The use of an incorrect number of shims (five instead of the typical three) was a direct result of the improper rigging.
- Maintenance errors were compounded by a lack of detail in the operator's Temporary Revision, which did not specify the need for the rig pins.
- Inadequate handover procedures between the night and day shifts contributed to the uncertified task cards and the failure to complete function checks.