A Mechanic and Lead Mechanic were informed that rudder trim tab cables on a Cessna Citation 560 Ultra were found crossed; and the Trim Tab traveled in the opposite direction from what was commanded; when turning the Rudder Trim Tab Wheel. A Pilot noticed the incorrect tab movement during a preflight check; fifty-three flight legs after mechanics had changed the Trim Actuator.
Synopsis
A Mechanic and Lead Mechanic were informed that rudder trim tab cables on a Cessna Citation 560 Ultra were found crossed; and the Trim Tab traveled in the opposite direction from what was commanded; when turning the Rudder Trim Tab Wheel. A Pilot noticed the incorrect tab movement during a preflight check; fifty-three flight legs after mechanics had changed the Trim Actuator.
Narrative
I was Lead Technician on a Cessna 560 V Ultra working with another Technician. We were assigned the task of replacing the rudder trim actuator on a routine phase inspection. I observed that he had the correct part number actuator; and he was using the appropriate maintenance manual for the installation. I bought back (verified) the installation and the Technician put a separate discrepancy [Write-up] for required travel check and rigging into the work order because there was not enough time to complete the task. The next day I was assigned the same aircraft and had assigned Technician # 2 to do the rig and travel checks with Technician # 1 assisting; since he had installed the actuator. To the very best of my knowledge; all maintenance manual procedures were observed in the rigging and travel checks. Three days later; I was phoned at home by my Manager in hangar maintenance that the trim tab that we had worked on; was traveling in the opposite direction to what the cockpit control wheel [position indicated]; and [later] discovered that the trim cables were [found] crossed. I was also told that the aircraft had been flown over 50 flights and gone through several maintenance events. While the fact that no incidents or accidents were involved is good; I heard that the cause is being investigated and I would gladly cooperate in any way to help with any information in order to prevent such things from occurring in the future.
NASA callback
Reporter stated the maintenance manual says to check entire rudder trim cable run for the Cessna V Ultra. But the manual assumes the necessary panels are already removed from the fuselage. When they work the larger Cessna 560 Excels; all access panels are removed; including the panel below the horizontal stab and in the vertical stab. Instead they were looking through small holes and did not notice the rudder trim cables coming through the cabin aft bulkhead had been crossed connected to the eight inch section of drive chain gear sprocket that goes over the top of the trim actuator. The chain sprocket rotates the actuator; which turns a star wheel with another set of cables to input rods to move the trim tab.Reporter stated the trim actuator was replaced due to corrosion being found on the bolts that attach the actuator to the vertical stab structure. Reporter believes the Cessna 560 Autopilot inputs to the rudder; not the trim tab. But the trim tab is a flying tab that moves in the opposite direction of the rudder. Besides not seeing the crossed cables; their other mistake was not having better communication with the cockpit Mechanic while they were doing the rudder travel checks and making sure when they were calling out for rudder left and right; that the tab was moving in the opposite direction.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.