What happened
On June 22, 2017, at approximately 08:31 UTC, a Bell 204B helicopter was engaged in commercial external load operations near Alpbach, Austria. The flight was part of a specialized logging operation involving multiple rotations to transport loads using a 30-meter longline.
After completing 21 rotations, the pilot noted the low fuel warning light had illuminated. While attempting to return to the refueling site to drop the longline hook, the pilot experienced two abrupt, intermittent power fluctuations in the engine. This was immediately followed by a continuous and steady loss of engine power.
In an attempt to manage the emergency, the pilot maneuvered the aircraft away from the refueling site toward a nearby forest track. During the landing attempt, the helicopter touched down with a right-hand yaw, causing the main rotor blades to strike the rising terrain and resulting in damage to the tail boom. The pilot was able to exit the aircraft independently and was uninjured, but the aircraft was destroyed.
The investigation
The Austrian Federal Safety Investigation Board (SUB) examined the aircraft's maintenance history, flight preparations, and the technical components of the fuel system. The investigation included a technical analysis of the fuel control unit, specifically focusing on the fuel filter housing, the fuel control unit's fuel-out line, and the check and thermal relief valve assembly. Investigators also reviewed the pilot's flight experience, the aircraft's loading and center of gravity, and the operational procedures used during the specialized external load mission.