Beechjet 400
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Flight Crew Last 90 Days 137; Flight Crew Total 15756; Flight Crew Type 3243
Aircraft Equipment Problem Critical; Inflight Event / Encounter Loss Of Aircraft Control
Flight Crew Regained Aircraft Control; Flight Crew FLC Overrode Automation; Flight Crew Diverted
Aircraft
Flying From ZZZ to ZZZ1; 35 miles south from JAX at FL410; the airplane's nose went to a descent; I disconnected the autopilot and abruptly nose went to a 25 degrees nose down attitude. Crew started trying to get the airplane under control; we called Center and let them know of our situation and they cleared us to FL350; we told them that we couldn't level off so they cleared us to 15;000 ft. The memory items for runaway trim was accomplished and we got the airplane's control back; that was descending through FL350. We requested vectors to the nearest suitable airport so were vectored to JAX. Weather at JAX was VFR. Approach and landing performed with no problem.
Beechjet BE-400 Captain reported that a runaway trim event occurred during cruise. The flight crew was able to regain aircraft control and make a successful diversion and landing.