What happened
On July 20, 2015, a serious near-collision occurred approximately 1 NM southwest of Samedan Airport (LSZS) near a reporting point known as HN. An AgustaWestland AW109SP helicopter, registration HB-ZRR, operated by Schweizerische Luft-Ambulanz AG, was performing an approach using a specialized procedure. Simultaneously, a Grob G 109 B motor glider, registration HB-2088, was in its departure phase. The two aircraft experienced a dangerous proximity because the crews failed to establish visual contact with one another.
The investigation
The SUST investigation examined the flight paths, the use of collision warning systems, and the communication protocols at the airfield. The investigation looked into the configuration of the Flarm collision avoidance technology on both aircraft, the role of the airfield information service (FISO), and the validity of the specialized helicopter approach procedures used at Samed and the visibility of these procedures to other airspace users.
Findings
Several factors contributed to the incident. The primary cause was that the crews of the helicopter and the motor glider failed to establish visual contact. This was exacerbated by the fact that the airfield information service provided no traffic information to either crew.
Specific contributing factors included:
- The helicopter was operating with a high approach speed and a high rate of descent.
- The collision warning system on the HB-ZRR provided limited utility to the crew.
- The collision warning system on the HB-2088 was not perceived by the crew, partly because the pilot had not engaged the transponder and the system was incorrectly configured. Specifically, the Flarm device was set to identify the aircraft as a "glider" rather than a "powered aircraft," which affected the warning behavior and the type of traffic reported to other users.
- The specialized helicopter approach procedure used at Samedan involved crossing the runway axis and steep descents, which carried inherent risks. Furthermore, this specific procedure and the HN reporting point were not published, meaning other airspace users were unaware of the pattern.
Safety action
Following the investigation, the airfield operator established a Safety Committee to assess the risks of the HN route. To mitigate identified dangers, the operator implemented several measures, including the official publication of the HN route, a speed limit of 100 knots for the approach, mandatory traffic information from the FISO, and earlier calls to the FISO. Additionally, the SUST issued safety advisories regarding the proper configuration of Flarm systems to ensure accurate aircraft identification and warning behavior.