Summary
On 1 August 2020, a Robinson R44 Raven II helicopter, registered ZS-RDI, was involved in an accident at Cypherkuil Private Farm, approximately 10 nautical miles south-west of Colesberg in the Northern Cape Province, South Africa. The helicopter was being operated under commercial aerial work (Part 137) and was conducting a game culling operation. The two occupants—the pilot and a passenger—were uninjured, but the helicopter sustained substantial damage.
Flight History
The helicopter departed De Poort Private Farm near Colesberg at 1020Z, routing to Cypherkuil Private Farm with the intention of returning to De Poort after the culling operation. The pilot reported flying at low altitude, below 500 feet above ground level (AGL), while tracking springbok. During a right turn, the helicopter experienced a loss of tail rotor effectiveness (LTE). The helicopter began to spin clockwise. In an attempt to recover, the pilot increased collective pitch excessively, leading to a loss of control. The helicopter contacted the ground hard on its skids. The main rotor blades severed the tail boom, and the helicopter rolled onto its left side before coming to rest. There was no pre- or post-impact fire.
Pilot Information
The 35-year-old pilot held a valid Commercial Pilot Licence and a Class 1 medical certificate. He had accumulated 2548.9 total flying hours, with 2520.1 hours on the Robinson R44 type. His most recent flight in the accident helicopter was on 31 July 2020.
Helicopter Information
The Robinson R44 Raven II (serial number 2393) was manufactured in 2015. At the time of the accident, the airframe had 1687.2 total hours. The last maintenance inspection was conducted on 27 June 2020 at 1642.6 hours. The helicopter was powered by a Lycoming O-540-F1B5 engine and was equipped with standard navigational aids.
Meteorological Conditions
Weather information sourced from the South African Weather Service indicated wind from 140° at 2 knots, visibility of 10 kilometres or more, temperature 17°C, dew point -7°C, and no cloud cover (CAVOK).
Wreckage and Impact
The helicopter came to rest at GPS coordinates 30°46'45.54"S 024°39'27.85"E at an elevation of 4583 feet. Damage included the skids, fuselage, main rotor, and tail boom. The occupants exited the helicopter without assistance.
Analysis
According to the investigation, during the right turn at low altitude, the helicopter's airspeed decayed. The pilot likely increased engine power abruptly. However, the power required by the main rotor exceeded the available engine power, causing the main rotor rpm to decrease. Because the tail rotor rpm is tied to the main rotor rpm, tail rotor thrust diminished. Although the engine continued to provide maximum torque, the tail rotor could not generate adequate counter-torque, resulting in LTE. The helicopter spun, and the pilot's recovery technique—excessive collective pull—further degraded control. The low altitude prevented a successful recovery.
Probable Cause
Loss of control due to loss of tail rotor effectiveness induced by low main rotor rpm. The low main rotor rpm was caused by an abrupt increase in engine power following a reduction in the helicopter’s airspeed. Contributory factors included improper recovery technique and low-level flight resulting in insufficient height to recover.