What happened
The pilot was performing maneuvers to practice an autorotation when the engine ceased operation. During the procedure, the pilot rolled the throttle back to the idle position and lowered the collective. At that moment, a red warning light illuminated on the instrument panel, and the pilot noted that the engine had stopped running. The subsequent autorotative descent ended in a hard landing.
The investigation
An on-scene investigation confirmed that the flight and powerplant controls were operationally continuous and that there was sufficient fuel remaining in the helicopter's tanks. A test run of the engine revealed a low idle speed of 1,300 rpm.
Industry experts noted that an engine may fail if a rapid roll-off of the throttle occurs while the idle RPM setting is too low. Furthermore, the FAA Approved Flight Manual specifies that pilots should "split the needles" by lowering the collective while maintaining the throttle setting. This technique utilizes throttle correlation to establish a high idle RPM of approximately 2500 RPM, which is intended to prevent the engine from stalling or loading up during recovery.