On January 10, 1999, at 1805 central standard time (cst), a Beech C-45H, N165ZA, piloted by a commercial pilot, was substantially damaged when it exited the right edge of runway 35 (6,000' X 100' patchy snow-covered concrete) at the Rosecrans Memorial Airport, St. Joseph, Missouri, during its landing roll and nosed down. Visual meteorological conditions prevailed at the time of the accident. The pilot and pilot-rated passenger reported no injuries. The 14 CFR Part 91 demonstration flight was not operating on a flight plan. The flight departed St. Joseph, Missouri, at 1750 cst. According to the pilot, he was demonstrating a landing to the passenger. During the landing rollout the airplane began to drift toward the right edge of the runway. The pilot said he applied power to the right engine but it "...did not immediately develop the expected power." He said he lifted the tail of the airplane off the runway with the intent of doing a go-around. By the time the tail was into the air the airplane had exited the runway's right edge and rolled through "...loose snow approximately 8 to 12-inches deep...," according to the pilot. The pilot said the snow was "...coming over the cockpit and the engine's power was hesitating..." due to the snow ingestion into the engines through the air intakes. The on-scene investigation revealed that N165ZA exited the right edge of runway 35 at about a 45-degree angle beginning in an area where there was more patchy snow on the runway than visible concrete. The airplane's main landing gear tire tracks went about 400-feet through the snow before the airplane nosed over. A track made by the tail wheel through the snow was not observed. Snow was observed in the air intakes for each engine.