What happened
During flight, a corporate jet experienced a malfunction involving the loss of elevator trim control, known as a runaway trim. This failure caused the aircraft to enter an uncommanded nose-low pitch attitude. The pilot reported that the loss of trim authority made the aircraft extremely difficult to maneuver, noting that the physical forces required to move the elevator controls became exceptionally high.
Because the runaway trim condition was not immediately identified, the pilot found it difficult to troubleshoot the system while managing the intense control forces. Ultimately, the pilot elected to maintain the established heading and performed a ditching of the aircraft type into a nearby marine cove. There were no reported fatalities or injuries in this event.
Findings
Post-accident investigations and functional testing revealed a repeatable fault within the electric pitch trim printed circuit board (PCB). Specifically, the K6 relay on the PCB failed by remaining in a closed position. This failure allowed electrical current to continue driving the elevator trim motor, resulting in continuous nose-down trim.
Records indicated that the PCB had been recently replaced during a phase inspection. The replacement unit had previously been installed in another aircraft that had experienced a ground-based electric trim runaway. Although the manufacturer had tested the board and found no discrepancies before returning it to service, the component remained faulty.
The investigation identified a single-point failure of the K6 relay alongside a latent design flaw in the autopilot/trim disconnect switch. This design anomaly prevented the electric trim motor from disengaging while the autopilot was active. Following these findings, the FAA issued three airworthiness directives to address the issue, and the pitch trim PCB was subsequently redesigned.