What happened
On 22 November 2012, an Alouette III helicopter, registration ZU-RFB, was performing aerial work near Libode in the Eastern Cape Province. The aircraft was engaged in supporting the construction of a new power line for Eskom. After a period of inactivity due to local weather and industrial action, the pilot performed a thorough pre-flight inspection and refuelled the aircraft using fuel transferred from a larger storage tank.
Shortly after departing from Libode at approximately 1600Z, the aircraft suffered an engine failure. The pilot attempted to execute a forced landing on a nearby ridge. During the final phase of the maneuver, the left wheel struck the terrain contour, causing the tail boom to lift and the tail rotor to detach. The helicopter subsequently rolled over upon impact. The pilot sustained no injuries, though the aircraft suffered extensive damage.
The investigation
Investigators examined the aircraft's maintenance history, weather conditions, and the fuel system. The aircraft's maintenance records indicated that all annual inspections were up to date and no mechanical defects were noted prior to the flight. Meteorological data confirmed that weather conditions were good, with visibility being high and winds light, ruling out environmental factors as a cause.
Technical analysis focused on the fuel supply. Tests conducted on the fuel filter, the main fuel line, and the engine's internal booster pump all revealed a significant presence of water. Specifically, samples from the filter and the main line contained approximately a 50% mixture of water and fuel. While the fuel taken directly from the main tank showed minimal water, the contamination was clearly present within the lines and filters used during the flight.
Findings
- The engine failure was directly caused by fuel contamination involving a high concentration of water in the fuel lines.
- The pilot was operating under valid commercial licensing and medical certification.
- The aircraft was fully compliant with its authority to fly and maintenance requirements.
- The forced landing became unsuccessful when the left wheel caught the ground contour, leading to the structural failure of the tail boom.