What happened
On September 24, 2007, an Eurocopter AS350 B2 (registration HB-XVM) was performing a commercial cargo transport to a construction site in Nadro, Switzerland. The mission involved delivering pallets of bricks to a site that was inaccessible by road.
As the pilot approached the landing zone to deposit the first pallet, the intense rotor downwash from the approaching helicopter exerted significant pressure on the site. At the time, the construction site featured newly erected, freestanding brick walls that had been built only three days prior. The force of the downwash caused two 2.60-meter-high walls to destabilize and collapse. A construction worker, who was assisting the flight assistant at the drop zone, was struck by the falling masonry and sustained serious injuries.
The investigation
The investigation examined the site conditions, the flight preparation, and the personnel involved. It was established that the pilot had previously performed deliveries at this specific site and had opted not to conduct a new site survey because the previous mission had occurred before these specific walls were constructed. The investigation also reviewed the training of the flight assistant and the safety protocols regarding the presence of personnel in the landing area.
Findings
- The primary cause of the accident was a person being present in the danger zone of the unloading area when a wall collapsed.
- The collapse of the wall was directly triggered by the rotor downwash produced by the AS350 B2 during its approach.
- A contributing factor was the inadequate assessment of the construction site conditions, specifically the stability of the newly erected, freestanding brick walls.
- The investigation noted that while the flight assistant was wearing a protective helmet, the construction worker assisting him was not, and other workers were also present within the hazard zone.