Enstrom F-28F accident near Twin Falls, Idaho, March 27, 2013

The NTSB's narrative final · quoted from the NTSB record

The student pilot reported that, during the helicopter's fourth landing, the engine started to sputter and lose rpm. He lowered the collective and added power, and the engine rpm increased. When he raised the collective, the engine lost power again. As he turned the helicopter to land it on the runway, the engine lost total power, and he performed an autorotation to a field. During the landing, one of the helicopter's skids got stuck in soft dirt, and the helicopter subsequently rolled onto its left side. Postaccident examination of the airframe and engine revealed no flight control or fuel system continuity anomalies. The single-drive dual magneto, ignition harness, and spark plugs were removed for further examination. The examination revealed that the left distributor gear was internally timed to the counter clockwise (CCW) marking and that the right distributor gear was internally timed to the clockwise (CW) marking. However, both distributor gears should have been timed relative to the CCW markings in accordance with the magneto manufacturer's Service Support Manual. When one of the distributor gears is timed to the CW markings instead of the CCW markings, a four-teeth difference in timing between the gears can occur. According to the magneto service representative and the magneto manufacturer's magneto specialist, the four-teeth timing difference would only have resulted in faster wear on the magneto's internal components. Given that the magneto was recently overhauled, it is likely that the magneto was operating as designed at the time of the engine loss. The reason for the loss of engine power could not be determined.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.