What happened
On February 4, 2014, two professional pilots were conducting an oil pipeline inspection flight. The flight originated from Bonn-Hangelar (EDKB) with the destination of Stadtlohn-Vreden (EDLS). During the mission, the crew observed an excavator performing earthworks near the pipeline route. To assess the situation and inform the excavator operator of potential hazards, the crew performed a landing on a nearby meadow near Langenfeld.
Following discussions with the workers on the ground and consultation with the pipeline operator, the pilot attempted to resume the inspection flight. To establish a sufficient takeoff run into the wind, the pilot intended to hover at the northern end of the meadow. At approximately 09:40 local time, as the Cabri G2 transitioned into a hover, the aircraft began to rotate to the left around its vertical axis. The pilot initially managed to stop the rotation after approximately 90 degrees of yaw by applying right pedal. However, despite applying full pedal input, the helicopter continued to rotate increasingly to the left.
In an attempt to maintain control and avoid landing on the soft ground, the pilot did not immediately descend. As the rotation speed increased, the pilot attempted to regain control by adjusting the collective pitch. When these efforts failed, the pilot attempted to bring the aircraft down. During the maneuver, the helicopter rolled onto its left skid and came to rest on its left side. The crew was able to exit the heavily damaged aircraft without injury.
The investigation
The BFU examined the aircraft, which was a 2013 model with approximately 624 total flight hours. The investigation included a review of GPS data recorded by a SkyDemon device and a mobile tablet used during the flight. The BFU also reviewed the aircraft's maintenance history and the pilot's credentials. Following the occurrence of several similar incidents involving this model, the BFU conducted comparative flight tests between a Robinson R22, which uses a conventional tail rotor, and a Cabri G2, which utilizes a Fenestron system, to evaluate pedal travel and control responsiveness.