Robinson R22 BETA N226WM

The flight instructor and pilot receiving instruction (pilot), who held a private pilot certificate with an airplane single-engine land rating, departed on a flight to practice pinnacle landings at a location about 20 minutes from their departure airport. When they arrived at their destination, the pilot completed a high reconnaissance of the area before beginning a descent towards his selected landing site. He overshot the approach and entered a steeper approach at an increased descent rate. About 30 ft above the ground, the main rotor started to droop (lose rpm), and the helicopter began to settle as the instructor and the pilot heard the low rotor rpm horn accompanied by an illuminated low rotor rpm light. The student was instructed to lower collective and advance the throttle, which was already in the full-open position. The pilot also erroneously pushed the cyclic forward, which likely exacerbated the main rotor droop and further inhibited a successful recovery at their low altitude. The instructor took control of the helicopter and lowered collective, but the left skid contacted a large rock and the helicopter rolled left and came to rest on its left side. The instructor suggested that the governor may have been delayed in advancing the throttle when the main rotor speed decreased as this had occurred during practice flights earlier that day. However, during postaccident testing, the governor operated normally with no delay and there was no evidence found of preimpact mechanical anomalies with the governor. Further, the instructor was also aware of this deficiency before they departed on the accident flight and could have easily overridden the governor during the approach phase of the pinnacle landing. The postaccident examination discovered that the forward vee-belt had likely come apart during the accident flight; the time of the separation could not be determined due to lack of available evidence. The operator had been troubleshooting reported anomalies with the belt tension for several months prior to the accident, and the excess slack likely led to the forward belt jumping forward during startup and resulted in the destruction of the belt about 20 minutes later. Even if the helicopter was operating with one vee-belt during the approach phase of the pinnacle landing, it should have been able to complete a successful power recovery or make a forced landing on one vee-belt. The instructor had discussed and flown practice pinnacle approaches with the pilot prior to the accident flight. During the pinnacle approach, the instructor issued the appropriate recovery instructions to the student after the low rotor rpm warnings were observed in the cockpit. However, the pilot chose to apply forward cyclic momentarily contrary to the recovery procedure, which added forward airspeed and further drooped the rotor rpm. The pilot’s application of forward cyclic was likely a negative transfer of learning from his fixed wing flying experience. Although the instructor quickly intervened, the helicopter was descending rapidly at a low altitude and struck the ground before he was able to recover. As the instructor had operational control and responsibility for the safety of the flight, the accident was also the result of his delayed remediation from a low rotor rpm condition at a low altitude.

Quoted verbatim from the NTSB record.