On July 14, 2012, at 1750 central daylight time, a Robinson Helicopter Company model R44 II, N556MM, was substantially damaged when it impacted a ground-support vehicle while landing near Red Oak, Iowa. The commercial pilot was not injured. The helicopter was registered to and operated by Johnson Helicopter Services LLC, under the provisions of 14 Code of Federal Regulations Part 137 without a flight plan. Day visual meteorological conditions prevailed for the local aerial-application flight that originated from an agricultural field near Red Oak, Iowa, about 1745. The pilot reported that after takeoff he was unable to activate the motorized spray system after arriving at the field to be sprayed. He returned to the departure location in order to troubleshoot the inoperative spray system. As he maneuvered the helicopter to land next to a ground-support vehicle, the main rotor system impacted a landing platform installed on top of the vehicle. The pilot reported that after the impact there was a vibration throughout the helicopter and elevated cyclic stick pressures. The main rotor system, tail boom, and fuselage were damaged during the accident sequence. The pilot reported that there were no preimpact mechanical malfunctions or failures that would have precluded normal operation of the helicopter. The closest weather observing station was at Red Oak Municipal Airport (KRDK), located about 5 miles south of the accident site. At 1755, the KRDK automated surface observing system reported the following weather conditions: calm wind, visibility 10 miles, temperature 33 degrees Celsius, dew point 22 degrees Celsius, altimeter setting 29.97 inches of mercury. The sky condition was not reported.