What happened
On December 12, 2019, at approximately 08:20 UTC, an Eurocopter AS350 B3 was performing a commercial external load transport operation in Kitzbühel, Austria. The mission involved transporting stage equipment and scaffolding for a ski race.
After transporting a ground assistant to a drop-off point, the pilot returned to the pickup site and landed with the rotors running. A ground assistant prepared a 30-meter long sling assembly, consisting of a damper sling, a Dyneema rope, and a hook buoy. Before takeoff, a hook check was performed, testing both the electrical and mechanical release mechanisms; no irregularities were found. The ground assistant then attached the load and signaled the pilot for takeoff.
As the helicopter ascended vertically to approximately 30 meters, the tension in the line caused the external load hook to open unexpectedly. The falling load assembly struck a ground worker who was standing near the load. Although the worker attempted to jump aside, the damper sling struck them in the back, resulting in one serious injury.
The investigation
The Austrian SUB examined the aircraft, the cargo release mechanism, and the flight conditions. Investigators performed a detailed technical inspection of the cargo hook, which was conducted by the manufacturer. The investigation also included a review of the pilot's qualifications, the aircraft's weight and balance, and the weather conditions at the time of the accident.
Findings
- The unintended opening of the cargo hook during the lifting process was the primary cause of the accident.
- While the manufacturer's inspection of the hook revealed some defects in the mechanical release mechanism, these findings suggested the defects would more likely make a release more difficult rather than causing an accidental opening.
- The cargo hook installed on the aircraft was not equipped with a visual locking indicator, a configuration that is permitted but no longer supplied by the manufacturer in this specific setup.
- The pilot was fully qualified and the aircraft was within all weight and balance limitations.
- Weather conditions were favorable and did not contribute to the incident.