Incident Overview
On September 24, 2007, at approximately 14:15 local time, an accident occurred involving a Eurocopter AS350 B2 "Ecureuil" helicopter registered as HB-XVM. The incident took place in Nadro, a district of the municipality of Castaneda in the canton of Graubünden, Switzerland. The aircraft was operated by Heli Rezia AG for commercial visual flight rules (VFR) operations.
Operational Context
The helicopter was tasked with transporting construction materials to a building site located on a slope approximately 50 meters from the local road. The site was inaccessible by vehicle. At the time of the incident, the ground floor of the new structure had been concreted, and free-standing brick walls for the upper facade had been erected three days prior. These walls were 2.60 meters high and separated by a distance of 4.50 meters.
Sequence of Events
The pilot, a Swiss national with over 4,100 flight hours, arrived at the site after conducting a visual inspection from the air. A ground handler, an Italian national with five years of experience, had assessed the site as suitable for operations earlier that day. As the helicopter approached the unloading zone to deliver a pallet of bricks, the rotor downwash caused the newly constructed brick walls to become unstable and collapse.
Consequences
The falling masonry struck one of three construction workers present at the site, resulting in serious injuries to his legs. The ground handler, who was wearing a protective helmet, was not injured. The pilot aborted the unloading operation and departed the scene immediately after being informed of the injury. The helicopter sustained no damage, but third-party property damage occurred due to the destroyed house walls.
Investigation Findings
The Bureau for Aircraft Accident Investigation (BFU) determined that the accident was caused by a person being in the danger zone of the unloading area and being injured by a collapsing wall. The collapse was triggered by the rotor downwash of the approaching helicopter. A contributing factor identified was the poor assessment of the construction site conditions, specifically regarding the stability of the newly erected walls.