On June 27, 2003, at 2100 eastern daylight time, a Bell 47G-5A helicopter, N8413D, operated by Adventure Helicopters Inc., sustained substantial damage during an autorotation following an in flight loss of engine power near Sandusky, Michigan. Visual meteorological conditions prevailed at the time of the accident. The airline transport pilot and his two passengers reported no injuries. The 14 CFR Part 91 business flight was not operating on a flight plan. The local flight departed a private helipad near Sandusky, Michigan, about 2100. The pilot reported the engine failed at approximately 400 feet above ground level. The pilot noted he performed a 180-degree autorotation to the southwest. The pilot stated he thought "it was evident that [the helicopter was] going to land in a large drainage ditch. I elected to flare sooner than I wanted to avoid the ditch." The pilot reported the helicopter subsequently landed hard in a bean field. A FAA airworthiness inspector conducted an on-scene inspection of the helicopter. The inspection showed engine and control surface continuity and all cylinders exhibited compression. Both fuel tanks contained fuel and the spark plugs and exhaust tubes were clean. The two magnetos worked independently. The inspection revealed that the ignition switch had an internal fault.