On October 19, 2016, about 0910 mountain daylight time, an experimental amateur-built Jim Gray Rotorway Exec 90 helicopter, N716JB, was substantially damaged following a forced landing after experiencing a loss of engine power at the Caldwell Industrial Airport (EUL), Caldwell, Idaho. The private pilot and registered owner of the helicopter was not injured. Visual meteorological conditions prevailed at the time of the accident. The flight was being conducted in accordance with 14 Code of Federal Regulations Part 91, and a flight plan was not filed. The proposed local flight was originating at the time of the accident. In a report submitted to the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), the pilot reported that during the takeoff everything seemed normal. He then accelerated and began a slow climb. At between 15 to 20 ft above ground level and about 40 to 45 knots, the helicopter suddenly yawed right, followed by the engine losing power. The pilot stated that being so low he could not perform a normal autorotation. The pilot opined that he did a partial nose-up, collective-down maneuver, but due to the low altitude and not being able to maintain sufficient rotor rpm, he elected to land in the soft dirt off the side of the runway. A hard landing resulted in the helicopter coming to rest on its left side. The helicopter sustained substantial damage to the tail boom and horizontal stabilizer. Subsequent to a postaccident examination of the engine, which was performed by a Federal Aviation Administration aviation safety inspector, the inspector reported to the NTSB IIC that the pilot had recently changed the alternator belt, however, had failed to properly tighten the tension bolts, which resulted in inadequate voltage to sustain ignition, thus precipitating the loss of engine power and hard landing.