On November 2, 2018, about 1130 central daylight time, a Bell 47G-3B-1, N1159W, was destroyed when it was involved in an accident in Wichita Falls, Texas. The pilot sustained minor injuries and the certified flight instructor sustained serious injuries. The helicopter was operated as a Title 14 Code of Federal Regulations (CFR) Part 91 personal flight. The pilot reported that the purpose of the flight was to practice emergency procedures with a certified flight instructor (CFI). After completing four uneventful autorotations, they climbed the helicopter to an altitude of about 1,500 mean sea level and turned onto the final approach leg of the traffic pattern to conduct a ‘hydraulics off’ approach. Once established on final approach, the CFI reached down to turn off the hydraulic switch and the engine lost complete power. The pilot immediately gave the flight controls to the CFI, and he prepared for an autorotation in a nearby field. During the descent, the helicopter impacted powerlines before it landed hard. The main rotor blade severed the tailboom, and the helicopter spun before it came to rest on its side. The CFI confirmed that when he reached down to turn off the hydraulic switch the engine lost complete power. There were no abnormal noises, nor were there any indications of an impending engine failure. The CFI mentioned that the hydraulic switch is on the lower console, and he was unaware of any nearby switches that would have turned off the engine. During a postaccident examination by a mechanic and a Federal Aviation Administration inspector, no anomalies were noted with the engine that would have precluded normal operations. The spark plugs were removed and consistent with normal operations. The engine rotated smoothly; the valves moved freely and evenly, thumb compression was established, and spark was obtained from the magnetos. The engine controls remained attached to the carburetor, the mixture was locked to the full rich position and the carburetor heat was in the OFF position. The carburetor was disassembled, and no anomalies were noted with the internal components. The fuel strainer was removed from the engine and the screen/bowl were clear of debris. The oil filter was also removed from the engine and was clear of debris. At the accident site, the ignition switch was found in the BOTH position. The instrument panel was removed, the electrical wires were examined, and no abnormalities were noted. The ignition switch positions (RIGHT, LEFT, and BOTH) were tested and functioned normally. However, when the key was in the LEFT or RIGHT position, a movement of the key would temporarily ground the switch. It was noted that a long keychain attached to the key extended over the hydraulics switch when the key was in the ignition.