What happened
On July 8, 1998, a Bell 47 G-3 Soloy helicopter was performing low-altitude pest control flights over vineyards near Bernkastel-Mosel. Approximately eight minutes into the flight, the pilot heard a sudden drop in turbine noise, accompanied by both acoustic and visual low-RPM warnings. At the time of the malfunction, the aircraft was flying at an altitude of roughly 3 to 4 meters above the vines with an airspeed of approximately 30 knots. The pilot managed to reduce the airspeed before the helicopter settled into the vineyard. There were no injuries to the pilot, though the aircraft sustained heavy damage and damage was caused to the vineyard crops.
The investigation
The BFU investigation initially identified contamination within the fuel system at the crash site, although the fine filter located before the fuel control unit showed no defects. Following the recovery of the aircraft, the engine and fuel system were removed and sent to a maintenance facility for technical analysis. This examination revealed significant defects within the engine's N1 controller, which caused a substantial reduction in fuel delivery. Subsequent specialized testing of the controller identified a broken pressure diaphragm as the specific cause of the power loss.
Findings
- A broken pressure diaphragm within the N1 fuel controller caused a significant reduction in fuel flow.
- While contamination was present in the fuel system, it was determined that this was not a contributing factor to the engine failure.
- The loss of power rendered the accident unavoidable, as there was no suitable emergency landing site available in the immediate vicinity.