What happened
On 3 December 2018, a Robinson R22 Beta helicopter, registration ZS-RLV, was conducting a commercial flight near the Ventersburg district in the Free State Province. The mission involved searching for jackals near the Koolspruit River to protect local livestock. To improve visibility during the low-level search, the crew had removed both doors from the aircraft.
While flying at approximately 30 knots along a densely vegetated area, the pilot encountered a sudden gust of wind from behind. In an effort to maintain altitude and avoid a hazardous, eroded embankment, the pilot increased the collective pitch. This maneuver, combined with the wind conditions, led to a rapid decay in the main rotor RPM, triggering the low RPM warning horn and light.
Realizing the engine power was insufficient to maintain flight, the pilot attempted to turn the aircraft into the wind. The pilot managed to clear the embankment, but the loss of rotor energy necessitated an emergency landing. The helicopter touched down heavily on level ground, causing the right skid to dig into the soil and break off, which subsequently caused the aircraft to roll onto its right side. There were no injuries to the pilot or the passenger, though the aircraft sustained substantial damage.
The investigation
SACAA AIID investigators examined the aircraft's weight and balance, maintenance history, and environmental conditions. The investigation confirmed that the aircraft was within its maximum takeoff weight limits and possessed a valid Certificate of Airworthiness. The pilot held a valid commercial license and medical certificate.
Investigators also analyzed the meteorological data, noting a temperature of 33°C and a calculated density altitude of 7,653 ft. The investigation also noted that the pilot had been involved in three previous helicopter accidents since 2008.
Findings
- The primary cause of the accident was the decay of the main rotor RPM triggered by a sudden gust of wind during low-level maneuvering.
- High density altitude conditions significantly reduced the available engine power, as the aircraft utilized a normally aspirated engine.
- The pilot's attempt to clear an eroded embankment by increasing collective pitch contributed to the depletion of rotor energy.
- The engine power required to recover from the situation exceeded the power available, even after the pilot applied full throttle.
- The presence of inconsistent winds and dust devils in the area further complicated the flight conditions.