On August 15, 1995, at 0930 central daylight time, a Beech B-60, N999AB, registered to M-C Industries, Inc., of Topeka, Kansas, and operated by a private pilot, departed controlled flight during cruise, at 19,000 feet mean sea level (msl), near Salina, Kansas. During the recovery the airframe sustained substantial structural damage. The 14 CFR Part 91 personal flight was operating in instrument meteorological conditions. An IFR flight plan was on file. No injuries were reported by the pilot or three passengers. The flight departed Colorado Springs, Colorado, 0930 mountain daylight time, with the intended destination of Kansas City, Missouri. The pilot reported the flight entered into a light overcast layer over central Kansas. He stated that the forecasted weather for central Kansas was level 1 and 2 rain, no sigmets were reported. The pilot reported light rime ice began accumulating on the airplane's windshield and leading edge of the wing. The pilot stated he turned on the deicing heat to the windshield, pitot tube, vents, and propeller. The pilot stated the ice accumulation was not heavy enough to cycle the boots. Approximately one-half hour later, the airplane suddenly began to shudder and buffet. The pilot stated he quickly scanned the instruments, but was not able to determine a problem. He then noticed that the airspeed was decreasing and he assumed the pitot tube was blocked. After the pilot advised air traffic control of a problem and requested a lower altitude, the airplane rolled to the left and entered into a spin. The pilot stated he was able to regain control of the airplane at 14,000 feet msl. Air traffic control vectored him to the nearest airport for landing. The pilot stated that a few minutes later the airplane experienced a large bounce, like an "air pocket." One of the passengers described the bounce as if something was "lifted from [the] plane." The airplane landed without further incident. The pilot listed several lessons which he learned from this incident; pay closer attention to the instruments especially in icing conditions, watch for a drop in airspeed, believe the airspeed indicator because a shudder could be a stall, recognize a stall immediately, and the recover from a spin is stick forward with counter rudder. The pilot stated the flight "entered area with increased ice accumulation and [I] didn't notice."