What happened
On July 1, 2015, a serious near-collision occurred over the southern shore of Lake Silvaplana, approximately 7 km southwest of St. Moritz, Switzerland. The incident involved two AS 350 B3 helicopters operating under visual flight rules (VFR).
One aircraft, HB-ZLG, operated by Swiss Helicopter AG, was engaged in an external load operation, transporting a concrete bucket via a 15-meter sling from the Furtschellas cable car station to the Rabgiusa mountain restaurant. Simultaneously, another AS 3/350 B3, registered as HB-ZMU and operated by Heli Bernina AG, was flying in a southwest direction after departing Samedan Airport.
As the pilot of HB-ZMU followed the valley slope, they noticed a shadow on the surface of the lake and subsequently identified HB-ZLG climbing to the right. The pilot of HB-ZMU immediately initiated an abrupt upward and leftward evasive maneuver. The pilot of HB-ZLG, who was on the fifth rotation of the cargo transport, suddenly encountered the yellow helicopter appearing in their path. The closest encounter occurred at an altitude of approximately 2,035 meters, with a horizontal separation of only about 15 meters and a vertical separation of roughly 25 meters.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) examined the flight paths, technical equipment, and operational conditions. The investigation focused on the proximity of the two aircraft, the effectiveness of collision avoidance technology, and the information available to the aerodrome flight information service. Investigators reviewed flight recorder data from HB-ZMU, including moving terrain and collision warning system logs, and analyzed the communication and surveillance capabilities of the Samedan aerodrome service.
Findings
- The near-collision was caused by the late mutual visual detection of the two aircraft.
- A significant contributing factor was that only one of the two helicopters was equipped with an onboard collision warning system.
- The risk of the encounter was increased because the aerodrome flight information service had no prior knowledge of the external load operation occurring near Samedan.