On March 15, 2007, about 1530 eastern daylight time, a Robinson Helicopter Company R-44-II, N196DM, registered to and operated by a private individual, as a Title 14 CFR Part 91 personal flight, made an autorotative landing to a field in Miami, Florida. Visual meteorological conditions prevailed, and no flight plan was filed. The private-rated pilot and one passenger were not injured, and the helicopter incurred substantial damage. The flight originated at Opa Locka, Florida, the same day, about 1500. The pilot stated that while making a 180-degree turn at about a 10 to 15 degree bank angle to return to Opa Locka, Florida, the low rotor rpm warning came on, so he lowered the collective to regain rotor rpm, and then regained his altitude. He said that suddenly there was a "huge vibration" and there were no warnings on the panel, but the vibration seemed to worsen. He said the engine and rotor rpm were very high, well above the "red zone." According to the pilot, he immediately closed the throttle and then the rpm began to decrease. He then selected a field and made an autorotative landing. The pilot said that the field was uneven, and tailboom was separated during the impact or the landing flare. The NTSB, with the assistance of a representative from Textron Lycoming Engines, conducted a detailed examination of the helicopter and its systems. In addition, the engine was given a test-run, and no evidence of precrash anomalies were noted with the helicopter, helicopter systems, or engine.