What happened
On 23 April 2008, a private pilot operating a Bushbaby 450, registration ZU-DIM, was performing a flight originating from New Tempe Aerodrome. After completing an initial circuit and a touch-and-go, the pilot departed toward Krugersdrift Dam. During the return leg into New Tempe airspace, the aircraft's engine experienced a sudden power loss accompanied by a significant drop in RPM.
As the pilot attempted to compensate with more power, the engine began to vibrate violently. The engine eventually ceased functioning entirely. Despite two attempts to restart the engine, the pilot was forced to seek an emergency landing site. Due to the presence of power lines and a fence, the pilot opted for a landing in a nearby ploughed maize field. Upon touchdown, the soft, uneven ground caused the nose wheel to pull sharply to the left, leading the aircraft to strike the ground with its right wing and ultimately nose over into an inverted position. The pilot escaped the 0 fatalities incident without injury, though the aircraft sustained substantial damage.
The investigation
SACAA AIID investigators examined the wreckage and the engine components to determine the cause of the power loss. A detailed strip-down inspection of the engine revealed that a main bearing on the crankshaft had disintegrated. This failure released metal debris throughout the cylinder head cavities, which subsequently caused the rotary valve to seize and destroyed the brass gear.
Investigators also noted a lack of documentation regarding a propeller change performed by a previous owner. It was noted that the absence of records for this component change left the possibility open that a prior propeller strike might have caused undetected engine damage. The investigation confirmed that the weather conditions were clear and that the pilot was properly licensed and medically fit.
Findings
- The primary cause of the engine failure was the disintegration of a main bearing on the crankshaft.
- The secondary cause of the aircraft's nose-over was the use of unsuitable, soft terrain for the forced landing.
- Metal particles from the bearing failure caused a chain reaction, including rotary valve seizure and gear destruction.
- There was no documentation explaining why a new propeller had been installed on the aircraft.
- The pilot's decision to land in the field was constrained by nearby obstacles, including a fence and power lines.