What happened
On 2 October 2019, a training flight departing from Groutville Airfield in KwaZulu-Natal experienced a critical engine failure during the climb phase. The aircraft, a Solo Wing Windlass Aquilla with registration ZU-CVI, was being operated by an instructor acting as the pilot flying, accompanied by a student pilot.
As the aircraft reached approximately 300 feet (91 metres) above ground level, the engine lost power and subsequently ceased functioning. In an attempt to return to the runway, the instructor maneuvered the aircraft back toward Runway 2 and 3; however, the right-hand main landing gear struck a slope at the edge of the runway. This impact caused the pilot to lose control, sending the aircraft veering right into a harvested sugar cane field. During the sequence, the nose gear struck a rock and broke away, causing the aircraft to dig into the ground and nose over. While the aircraft sustained substantial damage, both occupants escaped without injury.
The investigation
SACAA AIID investigators examined the mechanical state of the engine and the fuel used during the flight. An inspection by the aircraft maintenance organisation found no mechanical or electrical anomalies within the engine itself. However, the investigation focused on the fuel supply, noting that the operator had recently transitioned to a new fuel supplier.
Testing conducted by the maintenance organisation provided significant evidence regarding the fuel. When fuel from ZU-CVI was used to top up another similar aircraft, ZU-BWI, the engine exhibited excessive smoke and stalled after approximately 20 seconds of full-throttle operation. Once the aircraft was refueled with the previous supplier's fuel, the engine performed normally. This led investigators to conclude that the fuel from the new supplier was either contaminated or, more likely, had been prepared with an incorrect fuel-to-oil mixture ratio.
Findings
- The engine power loss and subsequent stoppage were likely caused by an incorrect fuel-to-oil mixture ratio.
- The aircraft lost control during the forced landing attempt because the right-hand main gear made contact with a runway slope.
- The flight was being conducted as a training flight under Part 96 regulations, though the operator did not hold an approved Aviation Training Organisation (ATO) certificate.