What happened
On November 15, 1981, at 15:49 local time, the pilot took off from Sion aerodrome in Switzerland aboard the Procaer F15B HB-EYE. The aircraft was carrying three passengers for a planned local VFR flight around the Matterhorn region. The flight plan indicated a duration of 80 minutes with an endurance capacity of 120 minutes, and the route was listed as Bagnes-Matterhorn.
The pilot had noted waypoints on a kneeboard, including Martigny, Fionnay at 6,000 feet, and Otemma at 10,000 feet. However, no one observed the actual flight path. The aircraft subsequently crashed onto the southern slope of Petit Mont Collon at an altitude of 3,200 meters. The exact time of impact remains unknown.
All four occupants were killed instantly upon impact, and the aircraft was destroyed. No other damages were reported.
The investigation
The preliminary investigation was conducted by Ernst Guggisberg and concluded with a report submitted on December 17, 1982. The investigation established that the pilot held a valid private pilot license issued in 1978, with recent experience transitions to the Procaer type in March 1981. At the time of the accident, the pilot had approximately 3 hours and 48 minutes of experience on this specific aircraft type.
The aircraft was airworthy, with its last control performed on December 5, 1980. It had accumulated 678 service hours. The mass and center of gravity were within prescribed limits. The fuel tanks contained approximately 140 liters, providing about four hours of endurance, despite the short planned flight.
Weather conditions at the time featured clear skies with unlimited visibility but strong northerly winds of 25 to 30 knots at 3,000 meters. Moderate turbulence was expected, particularly near the ground. The aviation forecast highlighted significant wind speeds and potential closures in Alpine passes.
Findings
The investigation determined that the accident was likely caused by insufficient altitude margin in an area with strong downdrafts and turbulence. The pilot was flying south of Petit Mont Collon, where the northerly wind created a zone of strong downdrafts. It is believed the pilot attempted a 180-degree turn near the Otemma glacier to continue toward the Matterhorn, likely because the downdrafts prevented maintaining the planned altitude.
Contributing factors included the pilot's underestimation of the wind's influence and his limited experience on the Procaer F15B. The clear weather may have led to a false sense of security regarding meteorological conditions. Additionally, the decision to turn was made too late for safe execution. The aircraft struck the glacier while banked at approximately 60 degrees, matching the slope angle.
Safety action
The report highlights the critical need for pilots to account for wind effects in mountainous terrain and to maintain adequate altitude margins when operating in areas prone to downdrafts. It also underscores the importance of experience on specific aircraft types when flying in challenging environments.