What happened
On the morning of 30 October 2008, a Sanka AK 1-3 helicopter, registration ZU-ETU, was conducting a private VFR flight from a heliport in Nelspruit toward Nkorho Bush Lodge. Approximately 42 minutes into the flight, the pilot experienced an engine failure. The pilot successfully executed an autorotation landing in an open, grass-covered area within the Sabi Sands Game Reserve.
While the landing itself was successful and the pilot sustained only a minor injury, the aircraft's engine exhaust gases ignited the surrounding dry grass. The pilot attempted to suppress the growing fire using the onboard portable fire extinguisher, but discovered the unit was unserviceable. The fire spread rapidly, eventually consuming the helicopter and leaving it destroyed.
The investigation
SACAA AIID investigators, with assistance from the aircraft manufacturer, examined the mechanical failures and the circumstances surrounding the fire. The investigation focused on the cause of the engine power loss and the failure of the fire suppression equipment.
Technical analysis of the engine components revealed that the Idler Actuator was defective, with a washer found seized inside the sleeve. This defect was linked to a tight fit in the assembly that caused internal scouring. Furthermore, the investigation looked into the service history of the fire extinguisher, finding that a recent inspection had been merely visual and the unit lacked a pressure gauge. The investigation also uncovered that the pilot's training was conducted by an Aviation Training Organisation (ATO) that lacked valid approval and authorization for helicopter instruction.
Findings
- The primary cause of the forced landing was inconsistent activity of the engine speed governor system, which led to engine RPM surging and a subsequent loss of rotor RPM.
- The engine failure was likely triggered by a defective idler actuator.
- The helicopter was destroyed by a veldt fire ignited by hot exhaust gases.
- The onboard fire extinguisher was not in a serviceable condition.
- The Pilot Operating Handbook (POH) lacked essential information regarding the engine speed governor.
- The pilot's type rating and private pilot training were completed through an unauthorized ATO.
Safety action
- It is recommended that the Commissioner review Type Acceptance approval in coordination with the manufacturer to ensure continued airworthiness of the Sanka AK 1-3 fleet.
- Owners of South African registered Sanka AK 1-3 helicopters are advised to replace existing fire extinguishers with known serviceable units.
- A review of training standards is recommended following the discovery of unauthorized training practices.