What happened
On 17 November 2023, a Windlass Aquila microlight, registration ZU-BGY, departed from Ballito Microlight Airfield in KwaZulu-Natal for a scheduled navigational training flight. The flight, conducted under Part 141 regulations, included an instructor and a student pilot. The weather conditions were clear with visual meteorological visibility.
Approximately 55 minutes into the flight, while the aircraft was cruising at 1,700 feet above ground level between Doringkop and Isithebe, the engine began running roughly and subsequently lost power. The crew attempted to troubleshoot the issue to restore engine performance, but these efforts were unsuccessful. Consequently, the crew performed a successful precautionary landing in a grass field located south of the Tugela River. There were no injuries and the aircraft sustained minor damage.
The investigation
Following the incident, the aircraft was transported by road back to the operator's base in Ballito. A post-incident inspection revealed that the propeller could not be rotated freely by hand. This led investigators to perform a teardown of the engine. The examination of the engine components identified significant mechanical wear within the internal assembly.
Findings
Technical analysis determined that the engine power loss was caused by extreme wear on the bronze spacers of the number 2 cylinder big end roller bearings on the connecting rod. This degradation was likely the result of insufficient lubrication within the bronze spacer. While the investigation noted a 30% probability of light carburettor icing at the time of the flight, the primary mechanical failure was the bearing wear.