What happened
On 18 May 2022, a Piper PA-25-235D Pawnee, registration ZS-BTL, departed from Potchef and intended to fly to Bospan Airstrip in the North West province. During the initial climb phase, approximately 300 feet above the ground, the pilot experienced a partial loss of engine power. The engine revolutions per minute (RPM) dropped from a required 2,575 to below 2,400.
Due to the low altitude and the proximity to the end of the runway, the pilot was unable to perform a turn back to the aerodrome. Seeking an emergency landing site, the pilot identified a grass-covered field. Upon touchdown, the aircraft entered a waterbed area, causing the main landing gear to sink into the mud. The momentum caused the aircraft to nose over, eventually coming to rest in an inverted position. The aircraft sustained substantial damage, but the pilot escaped the wreckage without any injuries.
The investigation
An investigation by the SACAA AIID examined the aircraft's fuel system and the circumstances surrounding the engine failure. Investigators found that while the fuel grade was correct, the fuel contained a significant amount of water. Evidence of rust within the carburettor suggested that water had been present in the fuel system prior to the accident. The investigation determined that the water disrupted the combustion process within the cylinders, preventing the engine from maintaining sufficient power for flight.
Findings
- The primary cause of the engine power loss was water contamination in the fuel.
- A contributing factor was the timing of the fuel sampling; the pilot drained the fuel samples too shortly after refuelling, which did not allow enough time for contaminants to settle into the tank drains.
- The aircraft's inability to maintain altitude during the climb necessitated the forced landing.