Accident Summary
On 30 May 2003 at 0905Z, a Jabiru SP aircraft registered ZU-CBL was conducting a private pilot licence (PPL) training flight near FASK (Swartkops Air Force Base). The flight, which departed at 0810Z, was accompanied by an instructor. After returning to the vicinity of FASK and while descending from 7000 ft to 6000 ft abeam the Atteridgeville quarry, the engine began running very rough and lost power. The instructor assumed control and attempted corrective actions including checking carburettor heat, fuel pump, and magnetos, but was unable to restore normal power.
Forced Landing and Outcome
The instructor elected to perform a forced landing on an open field west of the Erasmia neighbourhood. During the final approach, full flap was selected and the engine was switched off. The landing roll took place on uneven and rocky terrain, resulting in the collapse of the main undercarriage and nose gear. The instructor sustained back and neck injuries; the student pilot was not injured. No fatalities occurred.
Probable Cause
A steel washer of unknown origin was found lodged in the carburettor inlet. This restricted airflow into the carburettor, causing an excessively rich fuel-to-air ratio when the throttle was advanced beyond the quarter position. Although the origin could not be confirmed, it is possible the washer was introduced inadvertently during a routine maintenance inspection when the air box was open. Another possibility is that it entered via the carburettor fresh air inlet scoop on the left side of the aircraft, though this would require bypassing the air filter, which was considered unlikely.