Incident Overview
On 1 July 2015, a serious incident occurred between two AS 350 B3 helicopters over the southern shore of Lake Silvaplana, approximately 7 km southwest of St. Moritz, Switzerland. The helicopters were HB-ZMU, operated by Heli Bernina AG, and HB-ZLG, operated by Swiss Helicopter AG.
Flight Details
HB-ZMU was performing a cruise flight, while HB-ZLG was engaged in an external load transport flight and was in a climb phase at the time of the dangerous proximity.
Weather and Lighting
The meteorological conditions at the time included a general weather situation with good visibility. The sun position was such that visibility may have been affected.
Communication and Air Traffic Information
The aerodrome information service at Samedan did not have information about the external load flight operating near the aerodrome.
Collision Warning Systems
Only one of the two helicopters (HB-ZMU) was equipped with an onboard collision warning system (Flarm system). The other helicopter (HB-ZLG) had no such system installed.
Sequence of Events
The two helicopters approached each other without mutual visual detection until very late. The late visual perception and the lack of a collision warning system on one aircraft led to a dangerous proximity that could have resulted in a collision.
Cause
The serious incident was due to the dangerous proximity between a helicopter in cruise flight and a helicopter in external load transport flight in climb phase, resulting from the combination of the following factors: late mutual visual detection; only one helicopter was equipped with an onboard collision warning system. The occurrence was favored by the fact that the aerodrome information service did not have information about the external load flight near Samedan aerodrome.