What happened
On 1 September 2018, an Atlas Angel X328 (registration ZS-WZP) was performing a skydiving operation at a private farm airstrip near Delmas, Gauteng. While beginning its takeoff roll on runway 09, the pilot reached the rotation point approximately halfway down the strip. During this maneuver, the pilot observed via the digital engine display that the gas generator speed (N1) had dropped to 92%, falling below the required 96% to 100% range.
Due to the heavy weight of the aircraft and the insufficient power setting, the pilot decided to abort the takeoff. The aircraft was brought to a stop on the remaining runway, but the momentum caused it to overshoot the runway and strike a perimeter fence. The impact resulted in substantial damage to the aircraft's propeller, landing gear, and fuselage, though there were no injuries among the nine people on board.
The investigation
The SACAA AIID investigation focused on the mechanical cause of the power loss and the runway conditions. The aircraft was operating under Part 96 regulations for non-type certificated aircraft. Investigators found that the engine's compressor bleed valve had remained in the open position. This malfunction allowed compressed air to leak back into the compressor inlet, directly causing the reduction in engine power.
Further examination of the engine components revealed that the valve was likely contaminated. The investigation noted that the engine manufacturer defines polluted environments—which include dust, sand, and ash—as risks to the flow path. The airfield in question utilized a sand and grass runway surface.
Findings
- The primary cause of the power loss was a contaminated bleed valve.
- The contamination was attributed to a lack of a compressor wash following operations in an environment containing dust or sand.
- The runway excursion occurred because there was insufficient remaining runway length to stop the aircraft after the aborted takeoff.
- The aircraft's location near a perimeter fence left no buffer zone for an overshoot.