History of Flight
On 27 September 2011 at 0900Z, a Robinson R44 II helicopter (registration ZS-HFN) departed from Beestekraal private airstrip in the North West province for a game culling detail. The pilot, a 29-year-old commercial helicopter pilot with 2,662.8 total flying hours (375.4 on type), was accompanied by a passenger. According to the pilot, during the operation, as he attempted to chase game from under shrubs, the engine starter gear inadvertently attempted to engage with the engine ring-gear while the engine was running. The engine began misfiring with a loss of RPM, and the radio stack became inoperative.
The pilot executed an emergency landing. During the landing, the helicopter impacted tree branches and made a hard landing. The main rotor blades struck the tail boom, causing it to partially separate. The helicopter sustained substantial damage. Both occupants were uninjured.
Earlier Incidents
On 17 September 2011, the same pilot experienced a similar starter engagement during a game capturing detail near Vaalwater. The engine lost power but recovered after landing. Inspection revealed damaged starter gear teeth and a melted master radio relay (A999) with shorted terminals. The starter was replaced and wiring repaired. On 19 September, the helicopter was flown to an AMO at Wonderboom for further rectification and test flown without further issues.
Investigation Findings
The helicopter was recovered to an AMO at Wonderboom. Examination showed that the starter gear teeth exhibited excessive heat and fracture, with indent marks on the ring-gear. The master radio relay terminals were melted and shorted, causing electrical current to flow through wiring (582) to the starter motor relay, triggering the starter engagement. The current also reached the magneto start booster and magnetos, retarding timing and causing RPM loss.
Probable Cause
The probable cause was stated as: "Poor maintenance as a result of a defect not picked up on previous two occasions it occurred resulting on unsuccessful forced landing."
Damage and Injuries
The helicopter was substantially damaged: tail boom partially separated from main rotor impact. There were no injuries to the pilot or passenger.
Meteorological and Site Information
Weather was CAVOK with north-westerly wind and temperature 30°C. The accident occurred in daylight in an open field 2.5 nm from Beestekraal at coordinates S25°23'229" E027°37'.759".