Incident Overview
The aircraft experienced an uncommanded dive at approximately 11,000 feet above mean sea level (MSL), with recovery occurring below 2,000 feet MSL. During the descent, the pilot exceeded the never-exceed speed (Vne) while accommodating other air traffic.
Elevator Trim System Failure
Shortly after exceeding Vne, the elevator trim system malfunctioned and jammed the trim in the full nose-down position. A brief flare-up of smoke and sparks erupted under the right instrument panel on the left side of the control column. The pilot delayed an emergency declaration and did not relay information concerning the control problem.
Post-Incident Examination
Examination after the incident found the elevator trim tab cable broken at the trim servo, located under the aft cabin floor just forward of the cabin entrance door. The cable was frayed in an irregular manner over a nine-inch area. Loose cables became entangled in the electrical power diodes located beneath the control pedestal. Inspection revealed that the friction clutch operated at too high torque and that the cables were out of alignment, causing heat to other components.