What happened
On the afternoon of 10 September 2019, a Robinson R22 Beta helicopter, registration ZS-RMZ, was participating in a private game capture operation at The Hills Eco Estate. The mission involved herding a group of twenty-one zebras into a prepared boma. While the pilot was maneuvering at a low altitude to direct a group of animals, the aircraft entered a low main rotor RPM condition during a tight right turn.
The pilot was unable to recover the aircraft from this power loss. During the descent, the tail rotor blades made contact with tree branches, causing the tail rotor assembly and gearbox to separate from the tail boom. The helicopter subsequently yawed sharply before impacting a tree and rolling onto its right side in dense bush. The pilot, who was the sole occupant, escaped with minor injuries, though the aircraft sustained substantial damage.
The investigation
SACAA AIID investigators examined the flight conditions and the aircraft's configuration. The investigation confirmed that the helicopter was operating within its maximum takeoff weight, despite carrying 19 bottles of engine oil in the baggage compartment. The aircraft's maintenance records showed a valid Certificate of Airworthiness and a recent annual inspection.
Environmental factors were also analyzed. The investigation established that the flight took place in high-density altitude conditions, with a calculated density altitude of approximately 7,541 feet. The terrain in the maneuvering area was noted to be rocky and mountainous, with the flight path constrained by high-tension wires and estate perimeter fencing.
Findings
- The primary cause of the accident was the pilot maneuvering the helicopter at a low altitude during a game capture operation under high-density altitude conditions, which led to an unrecoverable low main rotor RPM.
- The high density altitude significantly degraded the performance of the normally aspirated engine.
- The maneuvering area was restricted by physical obstacles, including high-tension wires and estate boundaries.
- The loss of control was directly triggered when the tail rotor struck trees, leading to the structural failure of the tail rotor assembly.