Incident Overview
On June 2, 2020, at approximately 08:45 local time, a serious incident occurred involving an AS 350 B3 helicopter operated by Robert Fuchs AG. The aircraft was conducting commercial external cargo sling operations under Visual Flight Rules (VFR). The flight originated from a quarry area in Pfäffikon, Schwyz, with the destination being the island of Ufenau on Lake Zurich.
Operational Context
The helicopter was tasked with transporting materials for restoration work on the church tower on Ufenau. The operation involved 15 rotations to move various loads, including zinc-plated steel baskets (barells) containing aluminum scaffolding frames. During the first ten rotations, these baskets were transported individually or combined with other materials. For the eleventh rotation, the crew decided to transport two baskets simultaneously as a multiple load to optimize efficiency.
Sequence of Events
The two baskets, each weighing approximately 450 kg when fully loaded, were secured with textile slings and a horizontal tension strap. After lifting off, the pilot climbed to about 250 feet above ground level and accelerated to roughly 40 knots (75 km/h). The load subsequently disappeared from the view of the ground crew behind a warehouse roof. A witness on Ufenau observed the baskets swinging violently and colliding with each other. This impact caused the tension strap to fail, resulting in seventeen scaffolding elements falling into the water approximately 150 meters from the shore.
Investigation Findings
The Swiss Transportation Safety Investigation Board (SUST) determined that the cargo was not secured force-locked to the baskets; only four elements were stabilized by empty sleeves, while the rest stood loosely within the frame. The horizontal strap was insufficient to prevent movement. The investigation concluded that the large surface area of the stacked scaffolding created significant aerodynamic drag, causing the load to swing and collide at the chosen forward speed. The decision to transport two such inadequately secured loads as a multiple unit was deemed risky and poorly planned.