Cessna 560XL N108EK incident near Des Moines, Iowa

Probable cause

A temporary loss of control during cruise flight for reasons that could not be determined because postincident examination of the autopilot, pitch trim systems, and horizontal stabilizer revealed no anomalies consistent with a loss of control.

NTSB analysis

The flight crewmembers reported that, after about 10 minutes of cruise flight at 40,000 ft pressure altitude, they observed an autopilot pitch trim mistrim annunciation and an associated master caution indication. As they began to reference the applicable checklist, the autopilot automatically disengaged, the airplane suddenly pitched down, and the airspeed increased to about 30 knots over the redline. The flight crew regained control of the airplane and then leveled it at 33,000 ft pressure altitude. The flight crew subsequently landed the airplane without further incident. The autopilot was not used after the temporary loss of airplane control; however, the electric pitch trim was used after passing through 10,000 ft mean sea level, and it functioned normally. A postincident examination of the autopilot, pitch trim systems, and horizontal stabilizer did not reveal any anomalies consistent with a loss of control.

Text from the NTSB. Open the NTSB docket for CEN12IA554 for the full record.