Flight History
On Saturday, 8 July 1972, the pilot conducted a private flight from Ecuvillens to Ascona with three passengers aboard the Cessna 172 HB-CBN. Lacking extensive aeronautical experience, the pilot asked one of the passengers, who had 96 flight hours but an expired private pilot license, to handle navigation. At approximately 1300 hours HEC, the aircraft departed from runway 17 at Ascona airfield for the return flight. After takeoff, the pilot turned right, then made a wide climbing left turn over Lake Maggiore to the entrance of Val Verzasca. Continuing northwest at low altitude in a climb, the pilot entered a small, narrow, dead-end valley he thought would lead to Val Maggia. Realizing the error too late to turn back, the pilot allowed the aircraft to stall into trees on the southwest slope of the valley. The aircraft came to rest in a horizontal position, nose against the slope, at about 1310 hours at an elevation of 1000 meters above sea level, held by branches.
Damage
The pilot sustained minor injuries. The three passengers were uninjured. The aircraft was destroyed. Damage to vegetation was negligible.
Established Facts
The pilot, born in 1947, held a valid private pilot license and was authorized for the intended flight. Total flight experience was approximately 40 hours, including 5.21 hours on the accident type within the three months preceding the accident. The aircraft had valid airworthiness and registration certificates. The investigation revealed no pre-existing technical deficiencies. The weight and center of gravity were within permissible limits at the time of the accident.
Meteorological conditions in the accident area were: cloudiness 1 to 3/8 cumulus with base at 2500 m, visibility 20 km, light variable wind, temperature 28°C at Ascona and 24°C at 1000 m.
For the outbound flight, navigation was handled by one of the passengers. For the return flight, the distribution of tasks aboard was not clearly defined, and no precise route had been established.
Discussion
The pilot, aware of his modest experience, had asked a somewhat more experienced colleague to take charge of navigation for the outbound flight. This did not relieve him of also attending to this task for both flight preparation and execution. The return flight was not adequately prepared, which favored navigational errors.
The pilot's tactic of entering an unfamiliar valley at low altitude was also inadequate, as it deprived the pilot of any maneuvering margin and ultimately prevented turning back when the navigational error was recognized.
Conclusion
The commission unanimously concluded that the accident was due to insufficient altitude to ensure the necessary maneuvering margin during mountain operations and to inadequate flight preparation.