What happened
On 9 December 2013, a Bushbaby aircraft, registration ZU-CLM, was conducting a post-maintenance acceptance flight at Nelspruit Aerodrome (FANS). The flight was intended to verify repairs following a recurring issue with high engine water temperatures. The pilot, accompanied by a maintenance technician, performed a brief period of engine assessment before returning to the aerodrome for landing maneuvers.
While on a long final approach for runway 04, the engine and propeller suddenly ceased operation without warning. The pilot attempted to restart the engine twice but was unable to restore power. Recognizing that the aircraft could not glide back to the runway, the pilot declared an emergency and selected an open grass field for a forced landing. The aircraft touched down approximately 300 meters short of the runway threshold. Upon impact, the nose wheel and left main landing gear collapsed, causing the aircraft to strike the ground with its left wing. While the pilot escaped without injury, the passenger sustained a minor injury to his left knee.
The investigation
SACAA AIID investigators examined the wreckage and the fuel system of the ZU-CLM. The investigation revealed that the engine stoppage was not caused by mechanical failure, as compression tests and inspections of the spark plugs and fuel lines showed no abnormalities. However, investigators found no fuel in the carburetor bowls, the header tank, or the fuel lines leading to the pump.
Discrepancies were noted regarding the fuel state. While the pilot initially estimated 25 litres of fuel on board, his specific description of the tank levels (one at one-quarter and one at one-eighth) suggested a much lower total of approximately 13.5 litres. Furthermore, the investigation was complicated by the pilot's decision to add fuel to the left wing tank from a 20-litre container at the crash site before the aircraft was recovered, which prevented an accurate assessment of the original fuel levels.
Findings
- The engine stoppage was likely caused by fuel exhaustion.
- The pilot had difficulty accurately monitoring fuel levels due to the brownish color of the fiberglass wing tanks and the lack of a low-fuel warning system.
- The aircraft's fuel tank design was identified as a contributing factor, as it lacked the supplemental inspection lights found on other models of the same type.
- The pilot's post-accident actions of adding fuel to the tank jeopardized the integrity of the investigation.