On August 24, 2014, about 0650 Pacific daylight time, a Robinson Helicopter Company, R-44 II, N4246Z, sustained substantial damage while practicing an emergency autorotation, about 12 miles south of Pahrump, Nevada. The helicopter was registered to CSC Trust Company of Delaware Trustee and operated by the pilot under the provisions of Title 14 Code of Federal Regulations Part 91. The commercial pilot sustained minor injuries. Visual meteorological conditions prevailed and no flight plan was filed for the local personal flight that departed North Las Vegas Airport (VGT), Las Vegas, Nevada, about 0605. The pilot reported a total loss of engine power at about 3,500 feet, above ground level, while rolling the throttle back for a practice autorotation. He stated the throttle was rolled back smoothly and only enough required for a small tachometer needle separation. Subsequently, the pilot made several unsuccessful attempts to restart the engine. Unable to restart the engine, the pilot performed an autorotation emergency landing. The pilot further reported that during landing, the helicopter slid forward about 20 feet; at that point, the skids dug into the dry lake bed and the helicopter nosed over. Subsequently, the main rotor blades impacted the ground, and the helicopter rolled onto its right side. Examination of the helicopter wreckage by a Federal Aviation Administration inspector revealed that the main rotor blades and tail boom were substantially damaged. Additionally, fuel was observed leaking from both tanks at the site. According to the pilot, the fuel tank quantities were about 7/8's full just prior to the accident. The helicopter was recovered to a secure storage facility for further examination. Further examination of the helicopter by the National Transportation Safety Board investigator-in-charge and a Robinson Helicopter investigator revealed no evidence of any internal damage to the fuel injected engine or its accessories was observed. The oil dipstick reading indicated a normal quantity. Continuity with all the engine controls was established. The lower spark plugs were removed and examined and all sparkplug electrodes exhibited normal wear signatures when compared to the Champion Check-A-Plug comparison chart. The crankshaft was rotated by hand and compression was obtained on all the cylinders. It was determined that an engine run could be safety accomplished. The engine was subsequently test run, using an external battery source for electrical power, and functioned normally at various power setting. The magnetos were switched from left to right and the corresponding RPM drop was observed during the run. Fuel from the helicopter was used to ensure system continuity. The main fuel tank quantity indicated about 3/8's full and the auxiliary tank about 1/4 full. No engine anomalies were observed during the engine run. The helicopter's main gear box and drive system were examined and no anomalies were noted. Flight control continuity was established with the cyclic and collective. Tail rotor continuity was established in each direction from the separation point. A review of the helicopter's maintenance records revealed that the engine and airframe underwent their most recent annual inspection on December 04, 2013, at an airframe and engine total time of 444.3 hours. A Global Positioning System device was located in the wreckage and sent to the NTSB Vehicle Recorder Division for examination and readout. The device did not contain any specific information relevant to the accident.