On May 7, 2010, at 1732 mountain daylight time, a Robinson R22 Beta, N393LE, collided with terrain following a loss of engine power near Mendon, Utah. The certified flight instructor (CFI) and student were not injured; the helicopter sustained substantial damage. Mountain Ridge Helicopters was operating the helicopter under the provisions of Title 14 Code of Federal Regulations Part 91 as an instructional flight. Visual meteorological conditions prevailed, and no flight plan was filed. The CFI reported that he and the student were practicing autorotations. They entered into the first autorotation, rolled the throttle to idle, and the engine lost power. The CFI force-landed the helicopter in a field, and it rolled onto its right side. The CFI indicated that it appeared the grass-covered terrain was flat and would make a good emergency landing spot; however, upon touchdown he realized that the terrain was rough. A Federal Aviation Administration (FAA) inspector examined the helicopter. The engine was test run, and no anomalies were identified. During the examination and testing, the magneto internal timing and the magneto timing to engine was not verified prior to the removal and disassembly of the magnetos. Disassembly of the magnetos showed evidence of internal arcing. The last annual/100-hour inspection was on April 22, 2010, at a total time of 999.8 hours. The engine was equipped with TCM S4LSC-200 (left) and S4LSC-204T (right) magnetos. According to TCM Service Bulletin No. 515, Maintenance Intervals for all TCM and Bendix Aircraft Magnetos and Related Equipment (as well as Textron Lycoming Service Bulletin No. 515, All Textron Lycoming aircraft engines employing TCM and Bendix S-20, S-200, S-1200, D-2000, and D-3000 series magnetos and components), magnetos must be inspected at each 100-hour and 500-hour interval. The 500-hour inspection requires that the magneto be removed from the engine, disassembled, inspected, and serviced in accordance with the TCM Service Support Manual. According to the FAA inspector, review of the maintenance documentation for the helicopter showed that neither TCM SB 515 nor Textron Lycoming SB 515 was complied with.