Airprox between Cessna F172N and Pilatus PC-6 near Biel-Kappelen (HB-CNQ)

Incident Overview and Location On 26 June 2021, at 09:27 local time, a serious incident occurred approximately 1 nautical mile southwest of Biel-Kappelen Airport (LSZP). The event was classified as an airprox in Class G airspace, with no air traffic control service present. The minimum separation between the two aircraft was 0 nautical miles horizontally and approximately 300 feet vertically, at an altitude of around 650 meters above mean sea level. ## Aircraft and Operations The first aircraft was a Reims Aviation SA F172N, registered HB-CNQ, operated privately by Fluggruppe Seeland. The pilot, a Swiss national born in 1973, held an EASA Private Pilot Licence (Aeroplane) and had 362:38 total flight hours. The aircraft was on takeoff and climb from runway 23. The second aircraft was a Pilatus Aircraft Ltd PC-6/B2-H4, registered HB-FKP, operated by Parapro SA for parachute drop operations. The pilot, a Swiss national born in 1941, held an EASA PPL(A) and had 2,972 total flight hours. The aircraft was on approach to runway 05. ## Sequence of Events At 09:20, the PC-6 was climbing to the drop zone over the airport. At 09:24, it completed the parachute drop maneuver at approximately 14,000 feet AMSL and began a steep descent southwest. By 09:26, the PC-6 was at 5,000 feet AMSL, about 3 nautical miles southwest of the airport, and turned onto a crosswind approach to runway 05. The F172N began its takeoff roll on runway 23 at approximately 09:26. The PC-6 then turned left into an S-shaped final approach to runway 05. At 09:27:11, the PC-6 overflew the climbing F172N at approximately 900 feet above ground, with a vertical separation of about 300 feet. ## Findings and Analysis The published departure procedure from runway 23 involved a slight left turn after initial climb, while the published approach to runway 05 was straight along the runway axis. However, an internal document for parachute drop crews described an S-shaped approach to runway 05, opposite to the published departure from runway 23. The pilots reported that they had announced their intentions and runway directions on the radio. The PC-6 pilot stated he saw the Cessna and assessed the collision risk as non-existent. The F172N pilot stated he avoided a collision with a rapid and energetic elevator input. The F172N had a transponder but no collision warning device. The PC-6 had a Flarm system, which could not receive the Mode S transponder signal from the Cessna. Weather conditions were good for visual flight, with visibility over 8 km, light haze, and a cloud base at 4,000 to 4,500 feet AMSL. The investigation concluded that weather did not contribute to the incident. ## Contributing Factors The investigation identified the following factors: - Inadequate coordination between the two pilots - Absence of a collision warning device on the departing aircraft - Possible inadequate airspace surveillance The use of opposite runway directions at an uncontrolled airport requires careful airspace surveillance and precise radio communications. The investigation noted that the parachute drop approach procedure was not published on the Visual Approach Chart, which increased the risk of a dangerous approach.