What happened
On the morning of June 26, 2021, a near-collision occurred approximately 1 NM southwest of the Biel-Kaltelen (LSZP) airfield. A Pilatus PC-6/B2-H4, registered HB-FKP, was performing a parachute drop operation. After completing its drop maneuver at approximately 14,000 ft, the aircraft entered a steep descent. Simultaneously, a Cessna 172N, registered HB-CNQ, was beginning its takeoff roll from runway 23.
As the HB-FKP transitioned into an S-shaped approach for runway 05, it flew in the opposite direction of the departing Cessna. At 09:27:11 UTC, the two aircraft reached a minimum vertical separation of approximately 300 ft as the HB-FKP overflew the HB-CNQ at an altitude of roughly 900 ft above ground level. The pilot of the HB-CNQ reported that the collision was only avoided through a rapid and energetic pitch input.
The investigation
The investigation examined the flight procedures and equipment on board both aircraft. While runway 23 is the preferred direction for operations at LSZP, the parachute crew was utilizing a specific, non-published S-shaped approach for runway 05. This procedure is documented in internal instructions for parachute operators but is not depicted on the official Visual Approach Chart (VAC).
Investigators also reviewed the technical capabilities of the aircraft. The HB-CNQ was equipped with a Mode S transponder but lacked any collision warning systems. The HB-FKP was equipped with a Flarm system; however, this device was unable to receive the signal from the Cessna's transponder, preventing an automated alert.
Findings
- The primary cause of the airprox was the use of opposing runway directions by the two aircraft.
- Coordination between the two pilots was ineffective, despite both pilots stating they had broadcast their intentions via radio.
- The lack of a compatible collision warning system on the HB-CNQ removed a critical safety net that could have alerted the crew to the approaching aircraft.
- The use of non-published arrival procedures for parachute operations increases the risk of dangerous encounters in shared airspace.
- There was a potential lack of adequate airspace surveillance by the involved crews.