At about 1405 Eastern time, the airplane was substantially damaged when it experienced an in-flight upset while in cruise flight. The two commercial pilots were not injured. Instrument conditions prevailed and an IFR flight plan was in effect. The airplane was flying in smooth IMC conditions at FL200 with an area of “moderate to heavy to extreme” precipitation located about 30 miles to the northwest. As the airplane closed to 20 miles from the weather, it began to experience moderate turbulence and “several seconds of rime ice” on the windscreen. The crew deviated to the south but turbulence increased further for about 10 seconds. The airplane then entered an uncommanded left roll and dive. The autopilot disengaged and the pilots electrically driven attitude indicator tumbled. The flight crew reduced the engine power levers to idle and were able to recover the airplane utilizing the copilots vacuum-driven attitude indicator. The airplane was returned to straight and level flight at 8000 feet and was diverted to a nearby airport. Examination revealed the outboard one-third of the left elevator separated in flight and the outboard right elevator was deformed downward. The horizontal stabilizer bulkhead frame was fractured and the aft portion of the airframe was deformed.
