What happened
On 03 June 2009, an Alouette III SE 3160 helicopter, registration ZS-RJW, was conducting a ferry flight from Stutterheim to Hogsback in the Eastern Cape. The flight, operated under Visual Flight Rules, was being performed by a pilot and a passenger. Upon reaching the Hogsback area, the pilot identified an open grass field for landing.
During the final approach, the aircraft was approximately one metre above the ground when the pilot experienced a sudden, uncommand to the left. This sudden yaw was caused by a total loss of tail rotor control. In an effort to mitigate a hard impact, the pilot lowered the collective pitch to descend controlledly. However, as the aircraft touched the ground, the torque from the main rotor caused the helicopter to yaw and roll onto its right side. The impact resulted in substantial damage to the airframe and engine, though both occupants evacuated the wreckage without injury.
The investigation
SACAA AIID investigators examined the wreckage and recovered the broken tail rotor control cable for analysis. The investigation focused on the mechanical failure of the control system and the environmental conditions present during the flight. The investigation also reviewed the aircraft's maintenance history, noting its transition from South African Air Force service to private commercial use for firefighting operations.
Findings
- The primary cause of the loss of control was the failure of the tail rotor control cable.
- Investigators discovered a contaminant consisting of a mixture of dust and oil embedded on the cable.
- This substance created a sticky, abrasive compound between the cable and the pulley.
- The resulting friction between the moving parts caused the cable to chafe through its protective material and eventually break.
- It is noted that the aircraft's use in firefighting operations in remote areas may have allowed dust to enter the floor structure and reach the control components.