Introduction
On 15 April 2024, a Sling 4 TSi aircraft, registration ZU-MND, departed from Stellenbosch Aerodrome (FASH) on a private flight to Tedderfield Air Park. The flight was conducted under visual meteorological conditions by day. The aircraft was operated under Part 94 of the Civil Aviation Regulations.
Flight History
The pilot, a 23-year-old male with 101.6 total flight hours, had initially taken off from Swellendam Airport. After pre-flight checks there, the pilot noticed a low engine oil level and flew to FASH to obtain approved oil. One pint of oil was added to the reservoir per the Rotax operator's manual. The aircraft then departed FASH at 0830Z with two passengers.
Engine Problems and Emergency
Approximately 45 minutes into the flight, the engine oil temperature rose, though still within the green arc. The pilot reduced power as a precaution. Later, the oil pressure dropped, and the pilot felt an unusual vibration as the variable-pitch propeller automatically changed from coarse to fine pitch. The pilot reduced RPM and switched the propeller to manual control. The oil temperature moved into the yellow arc. The pilot decided to return to FASH and contacted Cape Town Flight Information Service (FIS) to report the problem. FIS cleared the aircraft to enter approach airspace. The oil pressure continued to drop, engine over-temperature warning lights flashed, and the temperature reached 130°C. The pilot shut down the engine, checked circuit breakers, and attempted an unsuccessful restart. He declared a Mayday emergency.
Forced Landing
The pilot identified a two-way road for a forced landing but observed traffic in both directions during the approach and decided to land on open ground to the left. A sudden strong wind from the south affected the aircraft, causing it to touch down on an uneven area with anthills and medium-sized rocks. During the ground roll, the aircraft struck anthills, damaging the undercarriage, rupturing the fuel tanks, and breaking one propeller blade. The lower airframe sustained substantial damage. All three occupants were not injured.
Investigation Findings
The investigation revealed that the number 2 piston had failed, leading to oil loss. Oil had passed into the combustion area and exited through the exhaust. The engine's oil pump was found normal and operational. Engine control unit (ECU) logs confirmed high oil temperatures in the cruise range, engine shutdown at approximately 1 hour 20 minutes, and an unsuccessful restart attempt. The aircraft had 84.6 Hobbs hours at the time of the accident; the last oil top-up was recorded at 76.2 Hobbs hours.
Probable Cause
The number 2 piston failed, which led to the loss of oil, an increase in engine temperature, and the loss of oil pressure; this resulted in the pilot executing an unsuccessful forced landing. No contributing factors were identified.