At 1216 Eastern time, the airplane was substantially damaged while landing. The Airline Transport pilot, the Commercial pilot and observer were not injured. Day visual conditions prevailed. The airplane landed on the main gear in a “firm but normal” landing approximately 1200 feet down the runway and within 4 to 5 feet to the right of the runway centerline. Immediately after touchdown, the pilots heard the landing gear warning horn sound intermittently for several seconds, and the right wing began to “drop.” The airplane then veered to the right, so the pilot took over the flight controls and attempted to stop the right wing from dropping, but the right propeller struck the runway. The airplane veered right coming to a stop. Moments later, the observer reported “fire right side,” and all three crew members evacuated out of the main cabin door after securing the airplane. Post-accident examination revealed the right main landing gear had penetrated the right main fuel tank. The pilot held a type rating for the BE-200 and total flight time of 7140 hours, with 900 hours in the BE-200.