Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Last 90 Days 200; Flight Crew Total 8400; Flight Crew Type 60
Aircraft Equipment Problem Critical; Deviation - Altitude Overshoot; Inflight Event / Encounter Loss Of Aircraft Control
Air Traffic Control Provided Assistance; Flight Crew Regained Aircraft Control; Flight Crew Overcame Equipment Problem; General Maintenance Action
Aircraft
After an uneventful departure; cruise and descent phase of flight while receiving radar vectors to the RNAV/GPS RW27 final approach course and descending through 4;500 feet altitude to the assigned 4;000 feet altitude we experienced a runaway pitch trim in the nose down direction. The aircraft immediately entered a greater than 3;500 FPM descent. I brought the throttles to flight idle while disconnecting the autopilot/trim disconnect switch to minimize the descent rate and manually returned the aircraft to the assigned altitude. We descended below 3;000 feet during the event. We notified ATC of our situation and intentions during the recovery. The flight continued to the destination without further incident under manual control. ATC handled our dire situation in a positive way providing assistance as requested. Upon arrival we had the aircraft inspected and found autopilot/electric trim operational abnormality.
King air C90 pilot experiences runaway trim during descent to 4;000 feet; resulting in momentary loss of control and descent below 3;000 feet. The autopilot/trim disconnect switch is used successfully to regain manual control.