Incident
A serious incident involving two aircraft occurred on 14 September 2019 at 15:14:08 local time in the Schimberig massif, approximately 10 km southeast of Schüpfheim, Canton Lucerne, Switzerland. The event was classified as an Airprox of ICAO category A with a minimum horizontal separation of 0 nautical miles and a vertical separation of 275 feet. No collision occurred, and both aircraft continued to their destinations without further incident.
Aircraft Information
Aircraft 1 was a Piper J3C-65/L-4, registration HB-OKP, owned and operated by Flying Ranch AG of Triengen. It was a single-engine high-wing aircraft, not equipped with a collision warning system but fitted with a transponder. The pilot, a Swiss national born in 1965, held a Private Pilot Licence (PPL(A)) issued by the Federal Office of Civil Aviation (BAZL) under EASA rules. He had accumulated 588:47 total flight hours, with 499:08 hours on type. The aircraft departed from Triengen Airport (LSPN) at 14:05 for a private sightseeing flight with one passenger. The pilot occupied the rear seat; the passenger was in the front.
Aircraft 2 was a Robin DR 400/140 B, registration HB-KDV, owned and operated by Segel- und Motorfluggruppe Grenchen of Grenchen. It was a single-engine low-wing aircraft equipped with a FLARM collision warning system and a transponder. The pilot, a Swiss national born in 1997, held a PPL(A) under EASA with 61:30 total flight hours, of which 26 hours were on type. The aircraft departed from Grenchen Airport (LSZG) at 14:45 for a private sightseeing flight with three passengers.
Sequence of Events
After approximately one hour of flight, HB-OKP was near the Pilatus region, flying on a southwesterly course west of Alpnach and Sarnen at a pressure altitude of about 7000 ft. The pilot had selected the Emmen airfield frequency (120.425 MHz) on his radio. Around 15:12, he turned right west of Lake Sarnen to head north towards Triengen, crossing the Glaubenberg and initiating a gentle descent. He reported that his visual scan was primarily focused ahead. Shortly thereafter, he saw another aircraft cross his field of view through the upper window in about one second at close range. The two aircraft crossed at 15:14:08.
The pilot of HB-KDV stated that neither he nor his passengers perceived the close approach during the flight. He had selected the Alpnach airfield frequency (128.475 MHz) and could not hear the other pilot. His FLARM system did not issue any collision alert.
Collision Avoidance Equipment
FLARM is a collision warning system for general aviation, used primarily in light and glider aircraft. It calculates future flight paths and broadcasts them via radio to nearby similarly equipped aircraft. It generates audio and visual warnings when a collision risk is detected but does not provide avoidance instructions. FLARM cannot detect aircraft equipped only with a transponder, as was the case with HB-OKP. The analysis noted that under the assumption of two appropriately reacting pilots, the near collision would most likely have been prevented by timely warnings from collision warning devices aboard both aircraft.
Meteorological Conditions
Weather at the time was sunny with no clouds, visibility greater than 10 km, and light wind from 240° at 2 knots at 2500 ft. Temperature was 17 °C with a dew point of 11 °C. QNH was 1021 hPa. No weather hazards were reported.
Reporting
The pilot of HB-OKP attempted to contact the other pilot after the event, informing him that he would report the incident via the EU occurrence portal. However, the required immediate report to the Swiss Rescue Alarm Center (Rega) as per Article 17 of the VSZV was not made. The pilot stated he was unaware of this reporting obligation. The pilot of HB-KDV contacted Grenchen flight school and was told that no further action was needed on his part, which did not align with the mandatory reporting rules to the Swiss Transportation Safety Investigation Board (STSB).