Incident
During an instrument descent from cruise altitude, the elevator trim cable failed. The crew experienced an increasing nose-down pitch that persisted regardless of control inputs. Despite the failure, the pilots successfully landed the aircraft by both pulling aft on the yoke to counteract the pressure. They also extended the flaps and landing gear 50 and 20 knots above their respective operating speeds, which reduced the trim forces and helped slow the airplane.
Investigation
Post-flight inspection revealed that the trim cable had been incorrectly routed around a cable guide during initial production. This routing error had not been discovered because the aircraft had not yet undergone its first required inspection, which would have allowed the discrepancy to be identified.
Probable Cause
The probable cause determined by the investigation was that the elevator trim cable failed due to incorrect routing around a cable guide during initial production. The discrepancy remained undetected because the aircraft had not reached its first required inspection.