Incident Overview
Following an annual inspection, the helicopter had exhibited an intermittent illumination of the 'ENGINE OUT' annunciator light. The pilot continued flying and monitored the engine instruments, particularly the N2 power turbine gauge.
Sequence of Events
During the accident flight, the annunciator light again flickered and then stayed on. Additionally, the 'ENGINE OUT' horn also sounded; however, the engine parameters remained normal. The annunciator light and horn are designed to activate if the N1 gas producer speed falls below 55 percent. The pilot reported that during a turn, the N2 began decreasing and he entered an autorotation. The helicopter rolled over following a hard landing.
Postaccident Findings
Postaccident tests revealed that the engine operated within normal specifications. The N2 tach generator operated normally. The N1 tach generator had failed.