What happened
On May 21, 2023, a series of dangerous encounters occurred in the airspace near Les Eplatures, Switzerland. Two gliders, an ASH 26 E (registration HB-2283) and an SZD-55-1 (registration HB-3118), had departed from Dittingen and Grenchen respectively, flying westward along the Jura mountains under Visual Flight Rules (VFR).
In the early afternoon, a P200 and6T (registration HB-LBU) departed from Speck-Fehraltorf on an Instrument Flight Rules (IFR) training flight, intending to perform two instrument approaches at Les Eplatures. While the crew of HB-LBU was in a holding pattern at approximately 7,000 ft, two separate close approaches occurred within a seven-minute window. At 15:00, the motor aircraft passed near the HB-2283 with a horizontal separation of only 0.1 NM. Seven minutes later, a much more critical encounter occurred between HB-LBU and HB-3118, with the aircraft crossing at a horizontal distance of just 0.03 NM and a vertical separation of only 50 ft.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) examined radar data, radio communications, flight recorders, and various video and webcam footage. The investigation focused on the flight paths of the three aircraft and the effectiveness of air traffic services in the Class E airspace surrounding the Les Eplatures control zone.
Findings
- The primary cause of the near-collisions was that the pilots failed to perceive the other aircraft in a timely manner.
- The encounters took place in Class E airspace, outside the control zone, which limited the ability of air traffic controllers to intervene or provide effective collision avoidance instructions.
- The presence of accumulating cumulus clouds at the flying altitude made visual identification of the other aircraft difficult.
- While the HB-LBU was provided with multiple traffic advisories by the Alps Radar approach control, the visual separation was not maintained.
- In the most critical encounter, the student pilot on HB-LBU only spotted the HB-3118 after emerging from a cloud, noting the red flashing light on the glider's canopy.
Safety action
Following the incident, the SUST issued a safety notice to all airspace users near Les Eplatures. The notice emphasizes the high risk of encountering VFR glider traffic in the Class E buffer zone, especially during weekends or favorable soaring weather. The notice also highlights the importance of using modern transponders, collision warning devices, and canopy flashing lights to increase electronic and visual visibility.