What happened
On May 25, 2014, an Alpi Aviation Pioneer 200, registered in France, was performing a local flight from the St Ghislain airfield (EBSG). Shortly after departing from runway 27 and beginning its initial climb, the engine began to vibrate heavily and lose power. The pilot was forced to execute an immediate forced landing in a nearby field.
During the descent, the pilot encountered a low-voltage power line and successfully cleared it. While attempting to land in the field, the pilot had to perform an emergency evasive maneuver to avoid a horse positioned in the landing area. This maneuver caused the aircraft to strike the ground on the left main landing gear, which subsequently ruptured, followed by the failure of the nose landing gear. The aircraft sustained significant damage to the fuselage belly, engine cowling, and propeller. The pilot escaped the wreckage without injury.
The investigation
Investigators focused on the fuel system to determine why the engine lost power. While the aircraft had sufficient fuel for the flight, the investigation revealed that the fuel levels in both carburetor bowls were abnormally low at the time of the accident.
Testing showed that while the electrical backup pump could eventually restore fuel levels, a leak was identified at a tee fitting on the suction side of the fuel system. This leak allowed air to be drawn into the fuel line. The investigation also noted that the fuel system had been modified two years prior to include an electrical pump, which introduced several new connections. Furthermore, the investigation found a lack of standardization in the various clamps and connectors used throughout the system, as well as discrepancies between metric and English unit measurements for some components.
Findings
- The engine stoppage was caused by fuel starvation resulting from air entering the fuel system through an improperly tightened fuel pipe clamp.
- The modification to the fuel system lacked an adequate quality control process to ensure the integrity of the new connections.
- Existing maintenance procedures were insufficient to detect the loose clamp during routine inspections.
- There is a lack of formal technical standards or specific guidance regarding the use of hoses and connectors in ultralight aircraft operations.