What happened
On 3 November 2018, a Robinson R44 Astro, registration ZS-RHY, was conducting a private pleasure flight near a farm in the Witbank area. The flight, which included the pilot and three passengers, was part of a series of local trips that day. While flying on the leeward side of high ground, the pilot executed a right-hand turn, at which point the low main rotor RPM warning horn activated.
In an attempt to recover, the pilot lowered the collective pitch lever; however, the rotor RPM continued to decrease. Lacking sufficient altitude to stabilize the aircraft, the pilot attempted a run-on landing on an open area of rocky terrain. The impact was severe enough to break the helicopter's skid gear. The aircraft skidded approximately 6 meters along its lower fuselage before the main rotor blades struck the tail boom, causing the helicopter to roll onto its left side. Despite the substantial damage to the aircraft, there were no injuries among the four occupants.
The investigation
The SACAA AIID investigation confirmed that the aircraft was within its allowable weight and center of gravity limits, operating approximately 16 kg below its maximum takeoff weight. The pilot held a valid private pilot's license and medical certificate, and the helicopter had a valid Certificate of Airworthiness and recent maintenance records.
Investigators analyzed the environmental conditions, noting a density altitude of approximately 6,228 feet and north-northeasterly winds of 15 to 20 knots. The investigation also examined the impact sequence, noting that the engine power required to recover from the RPM decay exceeded the power available, even after the pilot's corrective actions.