Baron 58/58TC
Flight Crew Commercial; Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 164; Flight Crew Total 21989; Flight Crew Type 912
Distraction; Time Pressure; Troubleshooting; Workload
Aircraft Equipment Problem Critical; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew FLC complied w / Automation / Advisory; Flight Crew Returned To Clearance; Flight Crew Took Evasive Action; General Maintenance Action
Aircraft; Weather
While on a vector for climb out I was assigned to maintain 7;000 feet MSL and advised of crossing traffic at 8;000 feet. As I approached the assigned altitude I engaged the ALT HOLD function on the Century IV autopilot. Immediately following that I received an advisory of adverse weather ahead from Center. Following that conversation I noticed that the altitude was approximately 100 feet high; so I depressed the pitch sync (control wheel steer) to reset the airplane in a gentle descent. I was startled by the yoke violently coming to the rear and putting the airplane in a somewhat severe nose high attitude. I recognized the situation as a runaway trim and depressed the autopilot disengage and trim interrupt button. By the time I wrestled the airplane to straight and level flight and turned off the electric trim I was at 7;400 and receiving a call from Center to confirm my altitude.Most of the airplanes I fly the pitch trim wheel is on the side of the console and I routinely rest my leg against the wheel and note any unusual rotation. This airplane's pitch trim wheel is enclosed in such a way that you physically have to reach for it to feel it. I assume that the trim was rotating to pitch up while the airplane was leveling and overpowering the autopilot when I noticed the slow climb and disengaged it. I completed the remainder of the flight with the electric trim turned off and the airplane is in the facility now getting the necessary repairs.
A BE-58 pilot reported a elevator trim ran away at 7;000 feet in level flight with traffic at 8;000 feet.