What happened
On September 2, 2009, an Eurocopter AS350 B3 helicopter, registration HB-XQJ, was performing external cargo operations at a construction site in Euloz, Fully. The mission involved transporting prefabricated wall elements for a single-story building using a long sling system.
During the operation, the pilot positioned the aircraft over the site to pick up transport equipment. To perform this maneuver, the pilot increased engine power, which intensified the downward airflow, or downwash, directly above the construction area. At that moment, a large south-facing wall panel, weighing approximately 40/0 kg, was being held in a vertical position solely by the physical strength of ground personnel. The intensified air movement caused the panel to lose stability and topple. A flight assistant, who was positioned within the danger zone while moving toward the site, was unable to escape the falling structure and sustained fatal injuries.
The investigation
SESA examined the operational procedures, the technical state of the aircraft, and the site safety protocols. The investigation confirmed that the pilot was properly licensed and the aircraft was operating within its weight and balance limits. No technical malfunctions were found in the Eurocopter AS350 B3.
Investigators also reviewed the meteorological conditions, noting that while local winds were light, the primary force was the aerodynamic disturbance created by the helicopter itself. The investigation focused on the sequence of events during the transition from hovering to translating, specifically how the increase in power during the equipment pickup contributed to the sudden surge in downwash pressure against the partially enclosed structure.