What happened
On 29 July 2003, a K-1200 helicopter, registration HB-ZEH, was performing logging operations near Frutigen, Switzerland. The aircraft was transporting tree trunks from a forest to a central landing area. During the fifth approach to the drop zone, the helicopter was carrying two tree trunks suspended vertically via a longline. As the pilot approached the landing area, the heavy logs impacted the ground with significant force, gouging the terrain. This impact triggered an uncontrolled opening of the lower cargo hook. The remaining sections of the logs fell from the hook, striking a third party on the ground. The individual, who was not part of the flight crew and was not wearing a safety helmet, sustained fatal injuries.
The investigation
The investigation conducted by the AAIB focused on the mechanical failure of the cargo hook and the ground organization at the landing site. Investigators examined the Canam C6/C60 cargo hook, which was attached to the longline. Testing later confirmed that the hook possessed a defective design that allowed for unintended release under dynamic loads. The investigation also reviewed the certification process of the equipment, noting that while the primary hook on the aircraft is strictly regulated, secondary remote hooks used for logging were subject to different, less stringent oversight. Furthermore, the investigators looked into the personnel and communication setup at the landing area at the time of the impact.
Findings
- The primary cause of the accident was the uncontrolled opening of the lower cargo hook due to its defective design.
- The certification process for the cargo hook was inadequate for the specific stresses of logging flight operations.
- The landing area was understaffed, with only one company flight assistant present.
- The presence of external helpers created a disorganized environment that was difficult for the flight assistant to oversee.
- Effective communication was hindered because the external ground assistants lacked radio equipment.
- The cargo hook lacked a proper declaration of conformity and CE marking according to relevant machinery directives.