What happened
On July 18, 2019, a Diamond DA42 NG, registration HB-LZH, was conducting a training flight from Bern-Belp to Ecuvillens. On board were a flight instructor and a student pilot. Simultaneously, a Piper PA-28-181, registration HB-PFS, was arriving at Ecuvillens from Saanen for a private flight, carrying a pilot and the aircraft owner.
As both aircraft approached Ecuvillens, the HB-LZH was in a continuous descent from 3,900 ft AMSL, flying a course that deviated from the recommended approach sectors. The HB-PFS was flying toward the downwind leg of runway 09. During the approach, the two aircraft crossed paths twice. The first crossing occurred at approximately 12:22 UTC, with a vertical separation of about 640 ft. The second crossing, which occurred during the HB-LZH's base turn, resulted in a much closer encounter. At 12:23:24 UTC, the aircraft were separated by only approximately 75 meters horizontally and 20 meters vertically.
The investigation
The investigation examined the flight paths, the use of communication, and the effectiveness of onboard collision avoidance technology. The investigators reviewed the use of the airfield frequency, where pilots are expected to broadcast position and intentions via blind transmissions. The investigation also looked at the flight procedures prescribed in the Visual Approach Chart (VAC) for Ecuvillens, which recommends approaching via the North or South sectors.
Findings
- The crew of the HB-LZH deviated from standard procedures by flying directly into the downwind leg rather than using the recommended approach sectors. Furthermore, the HB-LZH was in a continuous descent, which increased the risk of failing to visually detect lower-flying traffic.
- The crew of the HB-PFS heard a difficult-to-understand radio transmission from another aircraft in the North sector but failed to use the radio to clarify the situation, leading to incomplete situational awareness.
- The crew of the HB-LZH relied on the assumption that the HB-PFS would remain behind them after the first crossing, rather than actively seeking visual contact.
- Both crews failed to utilize available resources—including radio communication and the presence of a second crew member—to supplement the 'see and avoid' principle.
- The primary cause of the near-collision was that both crews continued their approaches with incomplete situational awareness without ever establishing visual contact with the other aircraft.