What happened
Following scheduled maintenance at a FAA certified Class IV repair station, an aircraft was released for service. The maintenance work had required that the spoiler control cables 17B and 18B be disconnected and subsequently re-connected.
After completing 52 flights, the aircraft experienced its first incident involving an uncommanded roll where the right wing dipped excessively. Following this event, maintenance was performed and the aircraft returned to service. Five flights later, a second incident occurred in which the aircraft abruptly rolled to the right. During the subsequent inspection, technicians found the right inboard spoiler cables were extremely loose; the cables were re-rigged, and the aircraft was returned to service.
Sixteen flights after the second repair, the aircraft experienced a third uncommanded right roll incident.
The investigation
Investigators determined that during the third incident, cable run 17B was riding on the lower side of the pulley for 18B and was running between the cable guards at the 18B pulley. Testing demonstrated that the 17B cable could be moved into the lower 18B roller slot simply by pulling down on the cable with a finger to position it into the pulley slot, without requiring any disassembly of parts or cable guides. A review of maintenance databases showed no previous recorded occurrences of cable misrouting in this specific area.