What happened
On 4 July 2024, a Just SuperStol, registration G-SSTL, was performing a private flight near Romsey, Hampshire. After completing engine warm-up procedures and taxi tests at Pauncefoot Farm Airstrip, the pilot attempted a takeoff to perform several circuits.
Shortly after becoming airborne, the engine experienced a period of power loss. While the engine power briefly recovered, a second loss of power followed. The pilot subsequently executed a forced landing in a field adjacent to the runway. During the landing, the aircraft entered a drainage ditch and struck a hedger and hazel bush, causing the landing gear to detach and the airframe to sustain significant distortion. The pilot sustained one serious injury.
The investigation
The AAIB examined the wreckage and analyzed engine data recorded by the aircraft's engine display. The investigation focused on the fuel system, which had recently undergone maintenance, including the replacement of fuel pipes.
Investigators found that the engine RPM and manifold pressure fluctuated significantly during the takeoff phase. The examination of the fuel system revealed that several installation features did not align with the manufacturer's build advice or the more recent Rotax Service Bulletin 912-079-R1. Specifically, the fuel suction pipe was routed in close proximity to the right rear cylinder exhaust downpipe without thermal insulation. Additionally, the fuel system utilized several right-angle connectors and banjo unions, which can increase pressure drops.
Findings
- The engine experienced intermittent power fluctuations during the high-demand takeoff phase.
- The fuel system installation did not fully conform to manufacturer recommendations, specifically regarding heat shielding and the use of certain connectors.
- The fuel suction pipe was located near a heat source (the exhaust downpipe), which may have contributed to fuel vaporization or cavitation.
- The aircraft relied solely on gravity feed to the diaphragm pump, as no electric backup pump was installed.
- The engine oversped briefly during takeoff, which may have indicated a leaning mixture as fuel levels in the carburettor float bowls dropped.