What happened
On September 15, 1981, two pilots, who were brothers, departed from Lugano Airport at 08:46 local time in a Piper PA-28RT-201T Turbo Arrow bearing registration HB-PET. Their intended destination was Paris-Le Bourget via a Visual Flight Rules (VFR) route. Shortly after takeoff, one of the pilots checked out on the ground frequency, but subsequent attempts to contact air traffic control in Milan, Zurich, or Geneva failed.
Approximately one hour later, at 09:45, two mountaineers located on the Schali Glacier near the Weisshorn heard engine noise that appeared erratic, suggesting the aircraft was maneuvering or searching for visual reference. The sound ceased abruptly followed by a dull impact. The wreckage was eventually discovered by a military SAR helicopter at 17:00 in a crevasse at the base of the Weisshorn's east face, at an altitude of 3,620 meters. Both occupants were killed instantly, and the aircraft was destroyed.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) conducted an inquiry focusing on the sequence of events and environmental factors. The investigation established that the aircraft was airworthy, with weight and balance within limits, and no mechanical failures were detected in the wreckage analysis. Propeller deformation indicated the engine was producing power at the time of impact.
Weather data revealed a warm front moving eastward with cloud bases rising from 1,500 to over 3,000 meters. Crucially, strong north winds created significant downdrafts and turbulence above the Alpine crest. Cloud tops over the Monte Rosa area reached Flight Level 155 (approximately 4,600 meters), effectively capping the peaks. The aircraft was not certified for flight in icing conditions.
Findings
The collision with the mountain occurred due to an unintended loss of altitude while flying above or between cloud layers. This descent was likely triggered by a combination of strong downdrafts, turbulence, and sudden structural icing upon entering the clouds. The aircraft's lack of de-icing equipment exacerbated these conditions.
Contributing factors included the pilots' low flight experience, with each having only around 60 hours total time on type. Their optimism regarding weather conditions over the Po Valley may have led to underestimating the difficulties of crossing the Alps. The erratic engine noise heard by witnesses suggests the crew was attempting to regain visual reference in deteriorating visibility.
Safety action
The report highlighted the risks associated with low-time pilots operating complex aircraft without instrument ratings in marginal VFR conditions, particularly regarding icing and mountain wave turbulence.