What happened
On 6 January 2012, a Thunderbird MK V microlight, registration ZU-BPC, departed from Eagles Creek Airfield for a private local flight. After the aircraft successfully took off, the pilot experienced a sudden loss of engine power during the climb out, which quickly progressed to a complete engine stoppage.
Unable to restart the engine, the pilot performed a forced landing in an open, grass-covered field near the airfield. While the initial touchdown was normal, the nose gear struck a tuft of grass and collapsed. This caused the aircraft to skid and eventually flip onto its roof, resulting in substantial damage to the airframe, including the cowlings and tail boom. The pilot escaped the wreckage without any injuries.
The investigation
SACAA AIID investigators examined the wreckage and the engine to identify the source of the power loss. The investigation focused on the fuel system and the engine's carburettors. The engine was recovered to an overhaul facility where technicians inspected the fuel bowls and the needle jets.
Investigators also reviewed maintenance records, noting that while the aircraft had been maintained by an approved organization, there was evidence that the owner had performed unauthorized maintenance in violation of regulations. The investigation also looked into the fuel source, as the pilot had refuelled from a drum earlier that morning.
Findings
- The engine failure was caused by fuel contamination within the system.
- Specifically, the carburettor needle jets were clogged with particles of sludge, which prevented sufficient fuel from reaching the combustion chamber.
- The sludge likely formed due to the blending of different fuel types or reactions involving moisture and oxidation.
- The nose gear failure and subsequent rollover were triggered by the aircraft hitting a tuft of grass during the forced landing.
- The pilot had performed a pre-flight inspection and found the aircraft to be serviceable prior to departure.