What happened
On the morning of 21 February 2023, a Robinson R44 Raven II helicopter, registration ZS-RTH, was engaged in a game darting operation at Brisbane Farm near Pomfret in the North West Province. The flight, conducted under visual meteorological conditions, carried a pilot and a veterinarian. The aircraft doors had been removed for the mission, which involved darting buffalo at low altitudes.
While flying approximately 40 feet above the ground, the pilot positioned the aircraft to allow the veterinarian to perform the task. As the pilot initiated a turn downwind following the operation, a low rotor RPM warning sounded. Due to the extremely low altitude, the pilot could not recover the necessary engine and rotor speed. The helicopter struck bushy terrain, causing the skid gear to be torn from the fuselage. During an attempt to flare before impact, the main rotor blades flapped downward and severed the aft tail boom. The aircraft subsequently rolled onto its right side. While there were no fatalities, the veterinarian was briefly trapped by their foot during the rollover before being freed by ground personnel.
The investigation
An investigation by the SACAA AIID established that the pilot was properly licensed and medically fit for the flight. The aircraft, ZS-RTH, was airworthy and had undergone its most recent maintenance inspection several months prior to the event. Meteorological data confirmed clear visibility and stable flying conditions at the time of the accident.
Investigators examined the flight dynamics and determined that the pilot was operating at a low forward speed of approximately 40 knots. The investigation focused on the sudden decay in engine and main rotor RPM that occurred during the maneuver.
Findings
- The primary cause of the accident was a decay in main rotor RPM during flight control manipulation, which prevented the pilot from maintaining altitude.
- The aircraft was operating at a low altitude within the critical danger area of the height-velocity diagram.
- The pilot performed a turn downwind while at a low altitude and low airspeed.
- The power required to maintain the maneuver exceeded the power available to keep the engine and rotor RPM within the safe operating range.