What happened
On April 7, 2018, at approximately 14:10 local time, a near-collision occurred approximately 2 km northwest of Buttwil airfield (LSZU). A Reims Aviation F1522, registration HB-CCN, was conducting a training circuit following a navigation flight. While turning into a left-hand final approach according to the Visual Approach Chart, the student pilot observed an Archaeopertyx electric-powered hang glider crossing the aircraft's path from left to right at the same altitude.
The pilot of the Archaeopteryx had departed from Buttwil for a local thermal flight. To avoid the intersecting path of the hang glider, the instructor of the HB-CCN took control of the aircraft and initiated a full left-hand turn. During this maneuver, the two aircraft closed to a distance of less than 200 m while maintaining the same altitude. Both aircraft subsequently returned to land at Buttwil.
The investigation
The investigation established that both aircraft were equipped with Flarm collision warning devices, though it could not be determined if any alerts were triggered during the encounter. The investigation also noted that the Archaeopteryx was one of three such motorized hang gliders based at Buttwil, operated by members of the local glider group. While regulations generally prohibit hang glider operations within 5 km of a civil airfield runway (or 2.5 km for helicopter pads) below 2,000 ft, exceptions in Buttwil may be granted by the airfield manager. The regular operation of these motorized hang gliders was conducted in coordination with the Buttwil airfield operator.
Findings
- The primary safety issue involved the close proximity of the two aircraft, which came within 200 m of each other at the same altitude.
- The flight instructor successfully executed an evasive maneuver to prevent a collision.