What happened
On June 6, 2013, at approximately 12:18 PM, a mid-air collision occurred near Gisliflue, in the municipality of Auenstein, Switzerland. The accident involved a Ventus 2b glider, registration HB-3373, and a Mooney M20J powered aircraft, registration HB-DFP.
The glider pilot had launched from Birrfeld airfield and was searching for thermals near the Jura mountains. Simultaneously, the crew of the Mooney M20J was conducting a flight for instructional purposes, flying from Lommis toward the Zurich area. As the glider pilot was scanning the sky for weather conditions, the powered aircraft approached from his right side.
The two aircraft collided at an altitude of approximately 1,285 meters (4,216 feet) AMSL. The impact caused the glider to become uncontrollable, entering a roll and a nose-down dive. Realizing the aircraft was no longer steerable, the pilot of the HB-3373 activated the canopy release and exited the cockpit via parachute. The pilot landed in a wooded area, sustaining one injury (light). The two occupants of the HB-DFP remained uninjured, though the aircraft sustained heavy damage.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) examined flight records from the glider's Flarm collision warning system, the powered aircraft's GPS, radio communications, and pilot statements. The investigation focused on the visibility of the aircraft to one another and the functionality of the onboard electronic warning systems.
Findings
- The primary cause of the collision was that both crews failed to actively monitor the airspace sufficiently.
- The Mooney M20J was not equipped with a collision warning system.
- A technical incompatibility existed between the aircraft: the signals from the HB-DFP transponder could not be received by the collision warning system installed in the HB-3373.
Safety action
- The SUST recommended that the Federal Office of Civil Aviation (FOCA) work with stakeholders to increase pilot awareness regarding collision risks and intensify training on the "see and avoid" principle.
- A recommendation was made for FOCA and EASA to develop a concept for implementing compatible, standardized collision warning systems for general aviation to ensure interoperability between different aircraft types.