What happened
Following the replacement of the forward elevator trim cable, the aircraft experienced a critical flight control failure during its initial departure. During the pre-flight phase, the captain failed to review the maintenance release documentation regarding the recent cable installation. Furthermore, the crew did not execute the required first flight of the day checklist, which would have included a specific verification of the elevator trim system.
Shortly after the aircraft departed the runway, the flightcrew reported a runway trim issue and attempted to manually select a nose-up trim position. Immediately following this action, the elevator trim moved to its maximum nose-down position. This resulted in control column forces increasing to 250 pounds, rendering the crew unable to maintain control of the aircraft type.
Findings
Investigations into the incident revealed that maintenance personnel had omitted a specific step required by the manufacturer's maintenance manual during the cable replacement process. Specifically, the crew failed to utilize a lead wire to ensure proper cable orientation. The investigation also noted that the maintenance manual contained an ambiguous illustration regarding how the cable should be routed around the elevator trim drum.
Testing conducted by the Safety Board on a similar aircraft demonstrated that a mis-rigged system could cause the elevator trim to operate in reverse. In these test conditions, activating the electric trim motor caused the trim tabs to move in the correct direction while the trim wheel moved in the opposite direction. Similarly, manual movement of the trim wheel resulted in the elevator trim tabs moving in the opposite direction of the intended input.