What happened
On 11 August 2019, a Robinson R44 Raven II helicopter, registration ZS-TTC, was conducting a scenic flight near Vaalwater in the Limpopo Province. The flight departed from a private farm with two passengers on board. During the flight, the helicopter was traveling at low speeds between 10 and 20 knots along the edge of the Vaalwater Dam.
As the aircraft moved near a treeline, wind and obstacles disrupted the airflow into the tail rotor system. This caused a drop in main rotor RPM and a subsequent loss of engine power. In an attempt to recover the rotor RPM, the pilot performed a flare maneuver. However, this maneuver caused the tail rotor system guard to strike the water surface, which led to the main rotors flapping downward and severing the aircraft's tail boom. The pilot attempted an emergency landing on the water, but the aircraft could not be controlled following the structural failure. The helicopter was eventually recovered from the dam, sustaining substantial damage to the tail boom, main rotor system, skids, and a window.
The investigation
SACAA AIID investigators examined the aircraft's performance capabilities relative to its operational environment. The investigation focused on the aircraft's weight, the altitude of the flight, and the aerodynamic conditions present at the time of the incident. The inquiry specifically looked at the pilot's weight calculations and the impact of the high elevation of the flight area on the helicopter's lifting capacity.
Findings
- The helicopter was operating at a weight of 2390 lbs, which was 270 lbs over the safe operating limit for the specific altitude and temperature conditions.
- The safe operating weight for the aircraft, considering the high elevation and ambient temperature, should have been no more than 2120 lbs.
- The pilot's initial weight calculation failed to account for how the high altitude and weather conditions would degrade the aircraft's performance.
- The aircraft took off in a direction toward high trees; because the aircraft was overweight, it lacked the necessary performance to clear these obstacles while transitioning to flying speed.