What happened
On 27 September 2011, a Robinson R44 helicopter, registration ZS-HFN, was engaged in a game culling operation near Beestekraal in the North West Province. While the pilot was attempting to move game from beneath shrubs, the aircraft experienced a sudden loss of engine RPM and the radio equipment became inoperative.
The pilot attempted an emergency landing in an open field. During the descent, the aircraft struck tree branches and experienced a hard impact. The force of the landing caused the main rotor blades to strike the tail boom, resulting in a partial separation of the boom from the fuselage. Despite the substantial damage to the Robinson R44, the pilot and passenger escaped with no injuries.
The investigation
Investigators examined the aircraft's history and found that a nearly identical mechanical failure had occurred ten days prior, on 17 September 2011. During that previous incident, the engine starter had inadvertently engaged with the engine ring-gear while the engine was running, causing power loss. Although the starter was replaced and the electrical system was repaired following that event, the failure recurred during the September 2/27 flight.
Technical analysis of the wreckage revealed that the soldering at the master radio relay (A999) had melted, creating a short circuit. This electrical fault caused the engine starter to attempt to engage the ring-gear while the engine was operational. Additionally, the current transfer to the magneto start booster caused the magneto timing to retard, further contributing to the loss of engine power.