What happened
On July 16, 2016, a Junkers Ju52, registration HB-HOP, was conducting a scheduled sightseeing flight from Dübendorf with 16 passengers and a crew of two. The aircraft was flying a route that included several Swiss lakes and mountain passes. Simultaneously, a pilot operating a Delta wing hang glider, known as an Atos, was flying north through the Schächental region.
As the hang glider pilot climbed to approximately 1,800 meters near the Pfifegg area, he spotted the Ju52 approaching from the south on a collision course. Believing the larger aircraft would maneuver around him, the hang glider pilot initially maintained his course. However, upon realizing the crew of the Ju52 had not seen him, the pilot was forced to initiate an abrupt descent to avoid a collision. The two aircraft reached a minimum horizontal separation of less than 100 meters and a vertical separation of less than 100 feet.
The investigation
SUST examined flight logs and GPS data from the hang glider to reconstruct the encounter. While the crew of the Ju52 reported seeing various aircraft that day, including a Delta wing, they estimated the horizontal distance to be greater than 200 meters and did not perceive the situation as a significant threat. In contrast, the hang glider pilot estimated the horizontal distance had closed to as little as 20 meters. The investigation also noted that the Ju52 was not equipped with GPS or any electronic flight monitoring devices that could have alerted the crew to the proximity of the other aircraft.
Findings
- The primary cause of the near-miss was the failure of the 'see and avoid' principle to maintain adequate separation.
- The crew of the Ju52 likely missed the close approach of the Atos, possibly due to the difficulty of monitoring airspace while managing a flight with many passengers.
- The lack of collision warning technology, such as transponders or FLARM-based systems, on the larger aircraft contributed to the danger of the encounter.