What happened
On 20 December 2001, a ZU-CAT was conducting a private flight, marking only its second flight since its maiden voyage. The aircraft departed from Brakpan Aerodrome with the intention of returning to the same airfield. Shortly after takeoff, the engine experienced a sudden loss of power, which prevented the aircraft from maintaining its altitude. The pilot was forced to perform an emergency landing on rough terrain located to the west of the aerodrome. While there were no fatalities or injuries reported, the impact with the ground resulted in damage to the aircraft's undercarriage.
The investigation
Following the incident, investigators conducted a detailed inspection of the engine components to determine the source of the power loss. During a dismantling process of the engine, technical teams identified a specific mechanical failure within the valve train. The inspection focused on the internal components of the cylinders to identify why the engine could no longer sustain flight.
Findings
The investigation established that the failure of a cir-clip was the primary driver of the accident. This specific clip, which was responsible for securing the hydraulic valve lifter of the number three-cylinder inlet valve, failed during flight. This mechanical failure rendered the valve inoperative, directly leading to the engine's loss of power. Additionally, the uneven nature of the landing site contributed to the structural damage sustained by the aircraft's undercarriage during the forced landing.