On January 30, 2007, approximately 1350 mountain standard time, a Cessna 421, N4584L, experienced the in-flight separation of the inboard half of the right elevator while en route from Idaho Falls, Idaho, to American Falls, Idaho. The commercial pilot, who was the sole occupant, was not injured. The 14 CFR Part 91 aircraft repositioning ferry flight, which had been airborne for about 10 minutes, was being operated in visual meteorological conditions. The aircraft is owned and operated by Bully Dog Technologies of Aberdeen, Idaho. No flight plan had been filed. According to the pilot, while he was climbing through 9,400 feet for 10,500 feet, he heard a very large thud that he could feel through the control yoke. The event moved the control yoke back and forth, and although the pilot was not sure what had happened, he later said that it felt as if something had "...struck the elevator very hard." At that point, the pilot reduced power and headed toward the Blackfoot Airport. Although there initially seemed to be no significant aerodynamic effect, after about 60 seconds a very strong shudder/vibration began to occur, and the aircraft began a dive to the left. The pilot then reduced power further to maintain control. He then looked over his right shoulder, and was able to see the right stabilizer/elevator "fluttering violently." He then further reduced the power on the right engine, and added power to the left engine, which effectively crabbed the aircraft to the right and reduced the airflow over the right stabilizer/elevator. After taking the aforementioned remedial action, the aircraft stopped shaking/vibrating, and the pilot turned toward Pocatello Regional Airport in order to make use of its longer/wider runway. The pilot was eventually able to execute an emergency landing at Pocatello. After exiting the aircraft, the pilot discovered that the inboard one-half of the right elevator had departed the airframe while in flight. A post-accident inspection by an FAA Airworthiness Inspector found that the bolt that connects the elevator trim tab actuator rod to the elevator trim tab horn was missing, and neither the actuator rod end nor the tab horn had failed. There was no evidence of a bird impact, and the pilot had not seen a bird at the time the event was initiated. In both his written statement, and during a post-accident telephone interview, the pilot stated that he had manually adjusted the elevator trim a number of times prior to the initiation of the sequence of events, and that not only did the system work correctly, but that he had felt no looseness, roughness, or vibration in the system. He further stated that because this was an FAA -approved ferry flight, he had performed an extensive preflight prior to departure, to include the flight controls and their actuation systems. He said that during this inspection he confirmed that there were no nuts or bolts missing from the flight control actuation system.