What happened
The pilot was engaged in a practice autorotation maneuver when he noticed an unusual sensation. To initiate the procedure, the pilot lowered the collective fully and reduced the throttle until the engine RPM and rotor RPM needles separated. Although the pilot confirmed that the needles had split, he noted that the aircraft did not feel normal.
In response to this sensation, the pilot decided to abandon the maneuver and applied power to attempt a recovery. During this process, the pilot observed that the engine and rotor RPM needles had synchronized at the correct positions on the tachometer face. However, during this period, the pilot became aware of an extremely high descent rate.
The investigation
The investigation found no apparent preexisting anomalies regarding the aircraft or its systems. The pilot's written report included no mechanical malfunction, and the procedures described in the pilot flight manual for practice autorotation—which involve splitting the needles by lowering the collective while maintaining throttle to establish a high idle RPM—were consistent with the pilot's actions.