Flight History
On 19 August 2017, a club member performed two flights with HB-PTL totaling 54 minutes. The aircraft was refueled with 81 liters of MOGAS, and later an additional 42 liters. The pilot, a Swiss citizen born in 1948, held a PPL(A) issued in 2015 and had nearly 200 total flight hours.
On 20 August, the pilot planned a private VFR flight from Bienne-Kappelen (LSZP) to Locarno (LSZL) with two passengers. At 10:15, the aircraft departed with the three occupants. The flight initially followed Lakes Bienne and Neuchâtel westward at about 4500 ft QNH, then turned left towards the Fribourg Alps and later southwest towards the Rhône delta. Radar contact ended at 10:49.
At 11:01, near Riddes at 4500 ft, the pilot contacted Sion aerodrome controller, asking about "Sion military". The controller informed him he had entered the Sion control zone without clearance. The pilot stated intentions to fly towards Brig and then return to land at Sion. HB-PTL landed on runway 25 at 11:38 and parked in area L.
Accident Flight
After a break, the pilot filed a flight plan for the return to Bienne-Kappelen, indicating a departure via point NW, then via Martigny and Payerne, with an estimated departure at 13:00 and endurance of 3:00 hours.
At 12:46, the pilot requested taxi clearance for a VFR flight to Bienne-Kappelen via the Sanetsch Pass. The controller cleared him to holding point B on runway 25 with QNH 1012 hPa. Shortly before 12:48, the pilot announced ready for departure. After clarification of the route, and because a following aircraft wanted to depart west under IFR, the pilot agreed to a left downwind climb for runway 25. Takeoff clearance was given at 12:48. At 12:51, the controller asked the pilot to report when ready to turn left towards the Sanetsch Pass. The pilot agreed, and the controller authorized the turn with instructions to report leaving the control zone, then gave QNH 1022 hPa.
At 13:02, the controller asked the pilot's altitude for coordination with a rescue helicopter; the pilot reported 4500 ft QNH. The controller passed traffic information. Soon after, the pilot announced leaving the control zone and was cleared to change frequency.
Witness Observations
Three ground witnesses observed the aircraft entering the valley at low height. Witness 1, a professional pilot near Dilogne at about 1600 m AMSL, saw the PA-28 coming up the valley, estimated its altitude about 200 ft below his position. Before reaching Dilogne, the aircraft executed a climbing left turn and headed back down the valley.
Witness 2, on the road near Cernet at about 1400 m AMSL, saw the aircraft above; the engine seemed to be producing power. His wife saw the aircraft turn left and go back up the valley.
About three minutes later, the aircraft reappeared near Witness 1 and continued towards the Sanetsch Pass at low altitude.
Witness 3, at 1790 m AMSL on the Sanetsch road above Sur Le Scex, observed the aircraft approaching the pass. Having taken a Sphair course, Witness 3 noted that the aircraft was flying much too low relative to the terrain.
Accident
The aircraft collided with terrain at Alpage de Tsanfleuron, Savièse, coordinates N 46°19'19" E 007°17'57", at 13:09 local time, at an altitude of 2100 m AMSL. The aircraft was destroyed. The pilot and two passengers sustained fatal injuries. Ground damage occurred due to post-impact fire.