Aircraft and Flight Details
On 15 October 2015, a Robinson R44 Raven II (registration ZS-RRZ) was engaged in a private game capture operation at Balmoral Farm in Ammerskloof, Mpumalanga Province, South Africa. The aircraft, manufactured in 2003, had accumulated 4256.6 total airframe hours. The engine was a Textron Lycoming IO-540-AE1A5 with 4256.6 hours since new and 2074.4 hours since overhaul. The helicopter was equipped with standard navigation and communication equipment, and no defects were recorded prior to the flight.
The pilot, a 23-year-old commercial pilot with 610.9 total flying hours (80.0 hours on type), held a valid license with a game capture rating. A passenger was also on board. The aircraft had sufficient fuel for the flight, with approximately half the fuel capacity at take-off.
Accident Sequence
The helicopter took off from Balmoral Farm at approximately 1245Z. After about 0.6 hours of flight, while hovering at an estimated height of 10-15 meters (32-49 feet) AGL to net livestock, an unusual loud noise was heard. The pilot observed a high engine RPM and low rotor RPM indication on the tachometer, accompanied by the clutch actuator caution light and Low Rotor RPM horn.
Deeming the situation critical, the pilot initiated an autorotation. He lowered the collective to reduce power, causing a rapid descent. Attempting to cushion the landing, he pulled collective shortly before impact. The helicopter struck the ground hard, coming to rest on its belly in an upright position. Damage was limited to the skids (which separated) and the tail boom. Neither the pilot nor the passenger sustained injuries.
Investigation Findings
The investigation revealed that the transmission failure resulted from the failure of the lower belt tension actuator bearing. The actuator assembly had been overhauled at 2182.2 hours, with 2074.4 hours flown since then—within the manufacturer's required overhaul interval of 2200 hours. No pre-existing defects were reported.
Further, the pilot was hovering at a height within the shaded “Avoid” area of the Robinson R44 Height/Velocity diagram, as specified in the Pilot’s Operating Handbook (POH). The POH advises against operating in this region because a power or transmission failure at that combination of altitude and airspeed reduces the ability to execute a safe autorotation. The pilot’s decision to autorotate from that height resulted in a hard landing.
Probable Cause
The aircraft experienced a transmission failure due to the failure of the lower belt tension actuator bearing. The pilot executed an autorotation from a hover height higher than that recommended by the Pilots operating handbook (POH) resulting on a hard landing and it came to rest on its belly.