What happened
On 27 November 2023, a student pilot was conducting a training flight in a Sling 2, registration ZU-IIL, departing from New Tempe Aerodrome (FATP) in the Free State province. The flight was intended for precautionary landing exercises and simulated engine failures. While climbing through approximately 5,200 feet near Krugersdrift Dam, the pilot observed the engine coolant temperature entering the caution range. In an attempt to stabilize the temperature, the pilot reduced engine power, but shortly thereafter, the electronic flight instrument system indicated low fuel pressure. The engine began to sputter and eventually stopped completely.
The pilot executed a Mayday call and glided the aircraft toward an open field. During the landing roll, the right main landing gear struck an anthill, causing the attachment bolt to dislodge and resulting in substantial damage to the aircraft. The pilot escaped the wreckage without injury.
The investigation
SACAA AIID investigators examined the circumstances of the engine failure and discovered that a second, similar occurrence involving a different Sling 2 (ZU-IEI) from the same flight school had occurred on the same day. In that instance, the engine also ran rough before the pilot was forced to land in a field.
An inspection of the fuel bowser pipelines by manufacturer representatives from The Airplane Factory revealed that the fuel being used was 93 Octane, which does not meet the minimum requirements specified in the aircraft's Pilot's Operating Handbook (POH). Laboratory analysis of the fuel sample confirmed that the 93 Octane fuel contained a high level of water, with a water content of 625.3 mg/kg, significantly exceeding the maximum allowable limit of 350 mg/kg.
Findings
- The aircraft was refuelled with 93 Octane fuel instead of the manufacturer-recommended 95 Octane or higher.
- The fuel used contained water sediments, which compromised the fuel's combustibility.
- The presence of water and the incorrect fuel grade led to the in-flight engine stoppage.
- The landing gear damage was caused by the impact with an anthill during the forced landing.