What happened
On the morning of 15 April 2024, a Sling 4 TSi aircraft, registration ZU-MND, departed Stellenbosch Aerodrome for Tedderfield Air Park. The flight, operated under private regulations, included the pilot and two passengers. Prior to the main leg of the journey, the pilot had stopped at Swellendam Airport to address a low engine oil level, adding only one pint of oil to the reservoir.
While navigating the Cape Town International Airport Terminal Movement Area, the pilot noticed rising engine oil temperatures. Despite attempts to manage the issue by reducing power and manually adjusting the propeller pitch, the engine's oil pressure began to drop significantly. As the oil temperature reached its maximum limit of 130°C, the engine could no longer be restarted.
Facing an imminent engine failure, the pilot declared a Mayday and prepared for an emergency landing. After determining that a nearby road was too heavily trafficked, the pilot opted for an open field near Touws River. During the descent, a strong southern wind pushed the aircraft into an uneven landing area characterized by rocks and anthills. The impact caused substantial damage to the airframe, including ruptured fuel tanks and a broken propeller blade, though all three occupants escaped without injury.
The investigation
SACAA AIID investigators examined the engine's Engine Control Unit (ECU) using Rotax-authorized diagnostic software. The logs confirmed a period of high oil temperatures followed by a total loss of oil pressure. A subsequent engine teardown revealed that oil deposits had been present in the exhaust system.
Findings
Technical analysis established that the failure of the number 2 piston was the primary driver of the accident. This mechanical failure allowed engine oil to escape into the combustion chamber, where it was heated and eventually exited through the exhaust valves. This leakage resulted in the depletion of the oil supply, leading to the observed spike in temperature and the subsequent loss of oil pressure that forced the pilot to terminate the flight.