Incident Description
On 22 July 2022, at approximately 1256Z, a Sling 2 aircraft with registration ZU-FCT departed from Brits Aerodrome (FABS) in North West Province, South Africa, on a private return flight to Wonderboom Aerodrome (FAWB) in Gauteng Province. The pilot, the sole occupant, had earlier flown from FAWB to FABS, conducted two touch-and-go landings and a full stop landing, then refueled. During the return flight, while overhead Klipvoor Dam at about 1500 feet above ground level, the engine lost power without warning. The left fuel tank was selected at the time. The pilot followed the engine power loss procedure from the Pilot's Operating Handbook, switching to the right fuel tank, but could not restore power. He broadcast a Mayday call on frequency 118.35 MHz to air traffic control at FAWB, then executed an emergency landing in a field north of FAWB. During the landing, the main landing gear separated from the underbelly and the nose gear strut broke. The pilot shut down the fuel selector, electrics, and master switch before disembarking. He was not injured, and no third-party damage occurred.
Aircraft and Pilot Information
The Sling 2 is a two-seat, single-engine, tricycle gear experimental-amateur built aircraft, powered by a Rotax 912iS engine. The aircraft was issued an Authority to Fly on 15 July 2016, with an expiry date of 30 June 2023. The last annual inspection was certified on 25 February 2022 at 2892.2 airframe hours, with a release to service valid until 24 February 2023 or 2992.2 hours. The aircraft had flown 86.15 hours since that inspection. No defect entries were outstanding before the accident flight.
The pilot held a South African Civil Aviation Authority (SACAA) Private Pilot Licence, revalidated from a UK CAA licence on 17 March 2022, and had a valid aviation medical certificate. He had 103.49 total flying hours, with 31.12 hours on type. His training was conducted by an approved training organization at FAWB.
Investigation Findings
Post-accident examination revealed no structural abnormalities; the cockpit was intact and flight controls continuous. The propeller showed damage consistent with low or no power. Fuel samples from both tanks were consistent with Mogas 95-octane fuel. The engine control unit (ECU) data showed a drop in exhaust gas temperatures for cylinders 1 and 3, indicating a lean mixture. Further analysis indicated that fuel injectors for cylinders 1 and 3 were obstructed. Spark plugs on cylinders 1 and 3 had carbon deposits, while those on cylinders 2 and 4 were normal. The fuel injectors were removed and tested at 40 psi; injectors for cylinders 1 and 3 exhibited irregular spray patterns due to dirt buildup in their nozzles. This dirt buildup explained the in-flight engine power loss. No other anomalies were found in the fuel system or engine.