Helicopter Rotor RPM Drop During Practice Autorotation Leads to Hard Landing (N2335Q)

What happened

The pilot initiated a practice 180-degree autorotation maneuver. During this phase of flight, the rotor rpm decreased to 73 percent. The pilot waited for the engine to bring back the rotor rpm but landed hard. The helicopter rolled onto its left side and the main rotor blades severed the tail boom. The pilot did not report experiencing any mechanical malfunction with the aircraft or powerplant prior to the accident.

The investigation

The investigation focused on the events leading up to the accident, specifically the autorotation maneuver. The pilot reported no mechanical issues before the incident. The hard landing resulted in significant damage to the helicopter, including a severed tail boom.

Findings

The primary finding was the decrease in rotor rpm during the practice autorotation. The pilot's decision to wait for the engine to recover the rpm contributed to the hard landing. The lack of reported mechanical malfunctions suggests the issue was related to the maneuver itself rather than a pre-existing aircraft defect.