What happened
During a cruise phase of flight, the aircraft suddenly pitched nose-down and began to vibrate significantly. The pilot took remedial action to regain control and subsequently made an uneventful emergency landing.
The investigation
A post-incident examination of the aircraft revealed that the bolt, nut, and cotter pin used to attach the elevator trim control rod to the elevator trim tab were missing. Company maintenance records indicated that these components had been removed on December 28, 1984, and were installed on the morning of the incident.
Findings
The sudden loss of pitch control was caused by fuel exhaustion due to the failure of the elevator trim attachment hardware. The missing fasteners allowed the trim tab to move freely, resulting in uncommanded nose-down movement.