Background
Three months before the accident, a mechanic repaired the left magneto. The magneto was reinstalled and timed with the right magneto. Later examination revealed that both magnetos had advanced timing. Internal inspection of the magnetos uncovered discrepancies that would lead to electrical breakdown.
Accident Sequence
Shortly after takeoff, the engine backfired. In response, the pilot in command attempted what appeared to be a backup autorotation intended to result in a run-on landing. Examination of the crash site showed that the vertical descent was arrested; however, the helicopter retained forward velocity. After touchdown, the helicopter slid through a ditch. The subsequent collision with the far side of the ditch resulted in fatal impact forces being transmitted to the pilot in command.
Investigation Findings
Investigators determined that the magnetos had been installed with advanced timing and that internal discrepancies could cause electrical breakdown. The crash site evidence indicated that the helicopter's forward speed had not been fully dissipated during the autorotation.