What happened
On August 24, 2021, at approximately 10:09 local time, a serious airprox incident occurred in the airspace near Emmen, Switzerland. Two aircraft were flying under Instrument Flight Rules (IFR) on converging flight paths at nearly the same altitude.
The first aircraft, a Pilatus PC-21 with registration HB-HZD, was conducting a training flight. The aircraft departed from Buochs Airport (LSZC) with a flight instructor and a student pilot on board, intending to return to the same airfield.
The second aircraft, a Textron Aviation 182T registered as HB-TLM, was engaged in a private flight. This aircraft departed from Triengen Airport (LSPN) with a pilot and one passenger, also destined for Triengen.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) initiated an investigation to determine the circumstances surrounding the close encounter. The preliminary investigation focused on the flight paths and altitudes of both aircraft at the time of the encounter. The investigation established that the two aircraft were on intersecting trajectories at a similar altitude, leading to the dangerous proximity.